Fragment原理Fragment实现原理Fragment实现原理Fragment实现原理Fragment实现原理Fr

基于Android Api 33

Activity的生命周期与Fragment生命周期的关联

示例代码

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/f1"
        android:text="Fragment 1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        />

    <fragment android:name="com.example.test_android.Fragment1"
        android:id="@+id/prefill_fragment"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        app:layout_constraintTop_toBottomOf="@id/f1"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintBottom_toTopOf="@id/content_fragment"
        />

    <FrameLayout
        android:id="@+id/content_fragment"
        android:background="#8EFDCB"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        app:layout_constraintTop_toBottomOf="@id/prefill_fragment"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintBottom_toBottomOf="parent"
        />

</androidx.constraintlayout.widget.ConstraintLayout>

import android.content.Context
import android.os.Bundle
import android.util.AttributeSet
import android.util.Log
import android.view.View
import android.widget.Button
import androidx.fragment.app.Fragment
import androidx.fragment.app.FragmentActivity

class MainActivity : FragmentActivity() {

    var f1: Button? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        Log.d("swithun-xxxx", "MainActivity onCreate")
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        f1 = findViewById(R.id.f1)

        f1()
        Log.d("swithun-xxxx", "MainActivity onCreate end")
    }

    override fun onStart() {
        Log.d("swithun-xxxx", "MainActivity onStart begin")
        super.onStart()
        Log.d("swithun-xxxx", "MainActivity onStart end")
    }

    override fun onCreateView(name: String, context: Context, attrs: AttributeSet): View? {
        Log.d("swithun-xxxx", "MainActivity onCreateView 1")
        return super.onCreateView(name, context, attrs)
    }

    override fun onCreateView(
        parent: View?,
        name: String,
        context: Context,
        attrs: AttributeSet
    ): View? {
        Log.d("swithun-xxxx", "MainActivity onCreateView 2")
        return super.onCreateView(parent, name, context, attrs)
    }

    override fun onAttachFragment(fragment: Fragment) {
        Log.d("swithun-xxxx", "MainActivity onAttachFragment")
        super.onAttachFragment(fragment)
    }

    override fun onResume() {
        Log.d("swithun-xxxx", "MainActivity onResume")
        super.onResume()
    }

    override fun onStop() {
        Log.d("swithun-xxxx", "MainActivity onResume")
        super.onStop()
    }

    override fun onDestroy() {
        Log.d("swithun-xxxx", "MainActivity onDestroy")
        super.onDestroy()
    }

    private fun f1() {
        f1?.setOnClickListener {
            val transaction = supportFragmentManager.beginTransaction();
            transaction.add(R.id.content_fragment, Fragment2())
            transaction.commit()
        }
    }
}

import android.content.Context
import android.os.Bundle
import android.util.Log
import android.view.Gravity
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.FrameLayout
import android.widget.TextView
import androidx.fragment.app.Fragment

open class Fragment1: Fragment() {

    open val name = "fragment 1"

    override fun onAttach(context: Context) {
        Log.d("swithun-xxxx", "$name onAttach")
        super.onAttach(context)
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        Log.d("swithun-xxxx", "$name onCreate")
        super.onCreate(savedInstanceState)
    }

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // 居中添加一个TextView——“hello Fragment1"
        Log.d("swithun-xxxx", "$name onCreateView")
        val view = TextView(context)
        val param = FrameLayout.LayoutParams(FrameLayout.LayoutParams.MATCH_PARENT, FrameLayout.LayoutParams.MATCH_PARENT)
        param.gravity = Gravity.CENTER
        view.layoutParams = param
        view.text = "hello $name"
        view.textSize = 15F
        view.gravity = Gravity.CENTER
        return view
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        Log.d("swithun-xxxx", "$name onViewCreated")
        super.onViewCreated(view, savedInstanceState)
    }

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        Log.d("swithun-xxxx", "$name onActivityCreated")
        super.onActivityCreated(savedInstanceState)
    }

    override fun onStart() {
        Log.d("swithun-xxxx", "$name onStart")
        super.onStart()
    }

    override fun onResume() {
        Log.d("swithun-xxxx", "$name onResume")
        super.onResume()
    }

    override fun onPause() {
        Log.d("swithun-xxxx", "$name onPause")
        super.onPause()
    }

    override fun onStop() {
        Log.d("swithun-xxxx", "$name onStop")
        super.onStop()
    }

    override fun onDestroyView() {
        Log.d("swithun-xxxx", "$name onDestroyView")
        super.onDestroyView()
    }

    override fun onDestroy() {
        Log.d("swithun-xxxx", "$name onDestroy")
        super.onDestroy()
    }

    override fun onDetach() {
        Log.d("swithun-xxxx", "$name onDetach")
        super.onDetach()
    }
}

class Fragment2: Fragment1() {
    override val name: String = "Fragment 2"
}

通过xml文件添加Fragment —— Fragment1

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    ...

    <fragment android:name="com.example.test_android.Fragment1"
        android:id="@+id/prefill_fragment"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        app:layout_constraintTop_toBottomOf="@id/f1"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintBottom_toTopOf="@id/content_fragment"
        />
    ...

</androidx.constraintlayout.widget.ConstraintLayout>

先从代码分析，从FragmentActivity.onCreate 开始看

[T-1] MainActivity.onCreate

    // MainActivity
class MainActivity : FragmentActivity() {
    ...
    override fun onCreate(savedInstanceState: Bundle?) {
   [:0] super.onCreate(savedInstanceState)
   [:1] setContentView(R.layout.activity_main)

关键节点 [:0] FragmentActivity.onCreate

[:0] FragmentActivity.onCreate

// androidx.fragment.app.FragmentActivity
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        ...
    [:0:1] mFragments.dispatchCreate();
    }

sequenceDiagram
autonumber

participant FragmentActivity
participant FragmentController

FragmentActivity->>FragmentActivity: onCreate begin
FragmentActivity->>FragmentController: dispatchCreate

classDiagram

class FragmentActivity {
    - FragmentController mFragments
}
class FragmentController

FragmentActivity --> FragmentController: hold

可以看出

FragmentActivity持有FragmentController
通知FragmentController分发create事件

[:0:1] mFragments.dispatchCreate()

// androidx.fragment.app.FragmentController
    public void dispatchCreate() {
   [:0:1:0] mHost.mFragmentManager.dispatchCreate();
    }

sequenceDiagram
autonumber

participant FragmentActivity
participant FragmentController

FragmentActivity->>FragmentActivity: onCreate begin
FragmentActivity->>FragmentController: dispatchCreate
FragmentController->>FragmentManager: dispatchCreate

classDiagram

class FragmentActivity {
    - FragmentController mFragments
}
class FragmentController {
    - FragmentHostCallback<?> mHost
}
class FragmentManager {
    <<abstract>>
}
class FragmentManagerImpl
class FragmentHostCallback {
    <<abstract>>
    - FragmentManager mFragmentManager
}

FragmentActivity --> FragmentController: hold
FragmentController --> FragmentHostCallback: hold
FragmentHostCallback --> FragmentManager: hold
FragmentManagerImpl --|> FragmentManager: implements

可以看出

FragmentController持有FragmentHostCallback持有FragmentManger
通知FragmentManager分发create事件

[:0:1:0] mHost.mFragmentManager.dispatchCreate()

// androidx.fragment.app.FragmentManager
    void dispatchCreate() {
        ...
   [:0:1:0:0] dispatchStateChange(Fragment.CREATED);
        ...
    }

public class Fragment implements ComponentCallbacks, OnCreateContextMenuListener, LifecycleOwner,
        ViewModelStoreOwner, HasDefaultViewModelProviderFactory, SavedStateRegistryOwner,
        ActivityResultCaller {

    static final int INITIALIZING = -1;          // Not yet attached.
    static final int ATTACHED = 0;               // Attached to the host.
    static final int CREATED = 1;                // Created.
    static final int VIEW_CREATED = 2;           // View Created.
    static final int AWAITING_EXIT_EFFECTS = 3;  // Downward state, awaiting exit effects
    static final int ACTIVITY_CREATED = 4;       // Fully created, not started.
    static final int STARTED = 5;                // Created and started, not resumed.
    static final int AWAITING_ENTER_EFFECTS = 6; // Upward state, awaiting enter effects
    static final int RESUMED = 7;                // Created started and resumed.

sequenceDiagram
autonumber

participant FragmentActivity
participant FragmentController
participant FragmentManager

FragmentActivity->>FragmentActivity: onCreate begin
FragmentActivity->>FragmentController: dispatchCreate
FragmentController->>FragmentManager: dispatchCreate
FragmentManager->>FragmentManager: dispatchStateChange

可以看出

FragmentManager内部分发Fragment.CREATED事件——Attached to the host

[:0:1:0:0] dispatchStateChange(Fragment.CREATED)

// androidx.fragment.app.FragmentManager
    private void dispatchStateChange(int nextState) {
        ...
       [:0:1:0:0:0] mFragmentStore.dispatchStateChange(nextState);
       [:0:1:0:0:1] moveToState(nextState, false);
       ...
}

public abstract class FragmentManager implements FragmentResultOwner {
    ...
    private final FragmentStore mFragmentStore = new FragmentStore();

sequenceDiagram
autonumber

participant FragmentActivity
participant FragmentController
participant FragmentManager
participant FragmentStore

FragmentActivity->>FragmentActivity: onCreate begin
FragmentActivity->>FragmentController: dispatchCreate
FragmentController->>FragmentManager: dispatchCreate
FragmentManager->>FragmentManager: dispatchStateChange
FragmentManager->>FragmentStore: dispatchStateChange

classDiagram

class FragmentActivity {
    - FragmentController mFragments
}
class FragmentController {
    - FragmentHostCallback<?> mHost
}
class FragmentManager {
    <<abstract>>
    FragmentStore mFragmentStore
}
class FragmentManagerImpl
class FragmentHostCallback {
    <<abstract>>
    - FragmentManager mFragmentManager
}
class FragmentStore

FragmentActivity --> FragmentController: hold
FragmentController --> FragmentHostCallback: hold
FragmentHostCallback --> FragmentManager: hold
FragmentManagerImpl --|> FragmentManager: implements
FragmentManager --> FragmentStore: hold

可以看出

FragmentManager持有一个FragmentStore
FragmentStore分发收到的状态nextState——Fragment.CREATED

[:0:1:0:0:0] mFragmentStore.dispatchStateChange(nextState)

// androidx.fragment.app.FragmentStore
    void dispatchStateChange(int state) {
        for (FragmentStateManager fragmentStateManager : mActive.values()) {
            if (fragmentStateManager != null) {
 [:0:1:0:0:0:0] fragmentStateManager.setFragmentManagerState(state);
            }
        }
    }

mActive是存储FragmentStateManager的Map:⬇️

// androidx.fragment.app.FragmentStore
class FragmentStore {
    ...
    private final HashMap<String, FragmentStateManager> mActive = new HashMap<>();

sequenceDiagram
autonumber

participant FragmentActivity
participant FragmentController
participant FragmentManager
participant FragmentStore
participant FragmentStateManager

FragmentActivity->>FragmentActivity: onCreate begin
FragmentActivity->>FragmentController: dispatchCreate
FragmentController->>FragmentManager: dispatchCreate
FragmentManager->>FragmentManager: dispatchStateChange
FragmentManager->>FragmentStore: dispatchStateChange
FragmentStore->>FragmentStateManager: setFragmentManagerState

classDiagram

class FragmentActivity {
    - FragmentController mFragments
}
class FragmentController {
    - FragmentHostCallback<?> mHost
}
class FragmentManager {
    <<abstract>>
    FragmentStore mFragmentStore
}
class FragmentManagerImpl
class FragmentHostCallback {
    <<abstract>>
    - FragmentManager mFragmentManager
}
class FragmentStore {
    HashMap「String, FragmentStateManager」 mActive
}
class FragmentStateManager

FragmentActivity --> FragmentController: hold
FragmentController --> FragmentHostCallback: hold
FragmentHostCallback --> FragmentManager: hold
FragmentManagerImpl --|> FragmentManager: implements
FragmentManager --> FragmentStore: hold
FragmentStore "1" --> "n" FragmentStateManager: hold

可以看出

FragmentStore持有n个FragmentStateManager
FragmentManager将收到的状态分发给每一个FragmentStateManager

[总结]: 由于FragmentActivity此时尚未setContentView，所以FragmentManger管理的Fragment数量实际上为0，mActive自然为0。但是我们仍然继续看下如果不为0会继续做什么。

[:0:1:0:0:0:0] fragmentStateManager.setFragmentManagerState(state)

// androidx.fragment.app.FragmentStateManager
    void setFragmentManagerState(int state) {
        mFragmentManagerState = state;
    }

// androidx.fragment.app.FragmentStateManager
class FragmentStateManager {
    ...
    private final Fragment mFragment;
    private int mFragmentManagerState = Fragment.INITIALIZING;

classDiagram

class FragmentActivity {
    - FragmentController mFragments
}
class FragmentController {
    - FragmentHostCallback<?> mHost
}
class FragmentManager {
    <<abstract>>
    FragmentStore mFragmentStore
}
class FragmentManagerImpl
class FragmentHostCallback {
    <<abstract>>
    - FragmentManager mFragmentManager
}
class FragmentStore {
    HashMap「String, FragmentStateManager」 mActive
}
class FragmentStateManager {
    Fragment mFragment
    int mFragmentManagerState
}
class Fragment

FragmentActivity --> FragmentController: hold
FragmentController --> FragmentHostCallback: hold
FragmentHostCallback --> FragmentManager: hold
FragmentManagerImpl --|> FragmentManager: implements
FragmentManager --> FragmentStore: hold
FragmentStore "1" --> "n" FragmentStateManager: hold
FragmentStateManager --> Fragment: hold

可以看出

FragmentStateManager 1:1 持有Fragment
FragmentStateManaget持有变量mFragmentManagerState——所属的FragmentManager的状态

至此，FragmentActivity将CREATE状态通知到FragmentManager进而通知到管理的每个FragmentStateManager——但是此时Fragment尚未更新。

[总结]: （只关心重要的FragmentActivity,FragmentManager,Fragment）

sequenceDiagram
autonumber

participant FragmentActivity
participant FragmentManager
participant Fragment

FragmentActivity->>FragmentActivity: onCreate begin
FragmentActivity->>FragmentManager: dispatchCreate() 分发CREATE

[:0:1:0:0:1] moveToState(nextState, false);

// androidx.fragment.app.FragmentManager
    void moveToState(int newState, boolean always) {
        ...
            mFragmentStore.moveToExpectedState();
        ...

sequenceDiagram
autonumber

participant FragmentActivity
participant FragmentController
participant FragmentManager
participant FragmentStore

FragmentActivity->>FragmentActivity: onCreate begin
FragmentActivity->>FragmentController: dispatchCreate
FragmentController->>FragmentManager: dispatchCreate
FragmentManager->>FragmentManager: dispatchStateChange
FragmentManager->>FragmentStore: dispatchStateChange
FragmentManager->>FragmentManager: moveToState

[:0:1:0:0:0:0]只是将用来管理Fragment的FragmentStateManager的状态更新了，这里才是真正更新Fragment的状态——但是此时FragmentManager管理的Fragment数量实际上为0，所以这里先不继续看，后续流程下面[:1:0:0:1]会继续讲到。

关键节点 [:1] setContentView(R.layout.activity_main)

[:1] setContentView(R.layout.activity_main) 执行[:0] super.onCreate(savedInstanceState)之后，setContentView

// androidx.activity.ComponentActivity
    @Override
    public void setContentView(@LayoutRes int layoutResID) {
        ...
    [:1:0] super.setContentView(layoutResID);
    }

sequenceDiagram
autonumber

participant FragmentActivity
participant FragmentController
participant Activity

FragmentActivity->>FragmentActivity: onCreate begin
FragmentActivity->>FragmentController: dispatchCreate
FragmentActivity->>Activity: setContentView

classDiagram

class FragmentActivity {
    - FragmentController mFragments
}
class FragmentController
class Activity

FragmentActivity --> FragmentController: hold
FragmentActivity --|> Activity

[:1:0] super.setContentView(layoutResID); ComponentActivity调用父类Activity.setContentView

// android.app.Activity
    public void setContentView(@LayoutRes int layoutResID) {
   [:1:0:0] getWindow().setContentView(layoutResID);
   ...

sequenceDiagram
autonumber

participant FragmentActivity
participant FragmentController
participant Activity
participant Window

FragmentActivity->>FragmentActivity: onCreate begin
FragmentActivity->>FragmentController: dispatchCreate
FragmentActivity->>Activity: setContentView
Activity->>Window: setContentView

classDiagram

class FragmentActivity {
    - FragmentController mFragments
}
class FragmentController
class Activity {
    - Window mWindow
}

FragmentActivity --> FragmentController: hold
FragmentActivity --|> Activity
Activity --> Window: hold

[:1:0:0] getWindow().setContentView(layoutResID); Window.setContentView

// android.view.Window
    public abstract void setContentView(@LayoutRes int layoutResID);

继续-跳过细节根据传入的layout ResId 初始化 view

// com.android.internal.policy.PhoneWindow
    @Override
    public void setContentView(int layoutResID) {
        ...
        [...]    mLayoutInflater.inflate(layoutResID, mContentParent);
        ...

sequenceDiagram
autonumber

participant FragmentActivity
participant FragmentController
participant Activity
participant PhoneWindow
participant LayoutInflater

FragmentActivity->>FragmentActivity: onCreate begin
FragmentActivity->>FragmentController: dispatchCreate
FragmentActivity->>Activity: setContentView
Activity->>PhoneWindow: setContentView
PhoneWindow->>LayoutInflater: inflate

classDiagram

class FragmentActivity {
    - FragmentController mFragments
}
class FragmentController
class Activity {
    - Window mWindow
}
class PhoneWindow {
    - LayoutInflater mLayoutInflater
}
class LayoutInflater

FragmentActivity --> FragmentController: hold
FragmentActivity --|> Activity
Activity --> Window: hold
PhoneWindow --|> Window
PhoneWindow --> LayoutInflater: hold

mContentParent为PhoneWindow的根View，下面会根据layoutResID构造View并add到mContentParent
继续-跳过细节根据传入的layout ResId 初始化 view

// android.view.LayoutInflater
    public View inflate(@LayoutRes int resource, @Nullable ViewGroup root) {
        return inflate(resource, root, root != null);

// android.view.LayoutInflater
    public View inflate(@LayoutRes int resource, @Nullable ViewGroup root, boolean attachToRoot) {
        [...] return inflate(parser, root, attachToRoot);
        ...
    }

attachToRoot为true(root != null)

    // android.view.LayoutInflater
    public View inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot) {
        synchronized (mConstructorArgs) {
            ...
                advanceToRootNode(parser); // 让parser移动到下一个要解析的"结点"
                final String name = parser.getName(); // 获取结点名字
                ...
                    // 根据名字构造xml的根view
                    final View temp = createViewFromTag(root, name, inflaterContext, attrs);
                ...
                    // 继续递归构造xml根view的子view，并addView到根view
                    rInflateChildren(parser, temp, attrs, true);

根据xml parser构造View，temp是xml的根标签代表的view，根据activity_main.xml xml-1 ⬇️

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout     ...>
    <Button..>

    <fragment android:name="com.example.test_android.Fragment1"...>

    <FrameLayout
        android:id="@+id/content_fragment"...>

</androidx.constraintlayout.widget.ConstraintLayout>

name则为根标签androidx.constraintlayout.widget.ConstraintLayout，
temp相应的则是androidx.constraintlayout.widget.ConstraintLayout，
下面rInflateChildren则是继续递归的构造ConstraintLayout中的子view。(开头的r代表的是Recursive--递归)

// android.view.LayoutInflater
    final void rInflateChildren(XmlPullParser parser, View parent, AttributeSet attrs,
            boolean finishInflate) throws XmlPullParserException, IOException {
        rInflate(parser, parent, parent.getContext(), attrs, finishInflate);

// android.view.LayoutInflater
    void rInflate(XmlPullParser parser, View parent, Context context,
            AttributeSet attrs, boolean finishInflate) throws XmlPullParserException, IOException {
        ...
            while (((type = parser.next()) != XmlPullParser.END_TAG ||
                ...
                final View view = createViewFromTag(parent, name, context, attrs);
        ...

rInflate: 继续递归构造temp的子view parser.next: 不断的获取下一个要解析的标签，根据xml-1，会解析到 <fragment标签——通过createViewFromTag构造Fragment

// android.view.LayoutInflater
    private View createViewFromTag(View parent, String name, Context context, AttributeSet attrs) {
        return createViewFromTag(parent, name, context, attrs, false);

// android.view.LayoutInflater
    View createViewFromTag(View parent, String name, Context context, AttributeSet attrs,
        ...
            View view = tryCreateView(parent, name, context, attrs);
        ...

构造fragment view

// android.view.LayoutInflater
    public final View tryCreateView(@Nullable View parent, @NonNull String name,
        ...
            view = mPrivateFactory.onCreateView(parent, name, context, attrs);
        ...

// android.view.LayoutInflater
    private Factory2 mPrivateFactory;

sequenceDiagram
autonumber

participant FragmentActivity
participant FragmentController
participant Activity
participant PhoneWindow
participant LayoutInflater
participant LayoutInflater-Factory2

FragmentActivity->>FragmentActivity: onCreate begin
FragmentActivity->>FragmentController: dispatchCreate
FragmentActivity->>Activity: setContentView
Activity->>PhoneWindow: setContentView
PhoneWindow->>LayoutInflater: inflate
LayoutInflater->>LayoutInflater-Factory2: onCreateView

classDiagram

class FragmentActivity {
    - FragmentController mFragments
}
class FragmentController
class Activity {
    - Window mWindow
}
class PhoneWindow {
    - LayoutInflater mLayoutInflater
}
class LayoutInflater
class `LayoutInflater-Factory2`

FragmentActivity --> FragmentController: hold
FragmentActivity --|> Activity
Activity --> Window: hold
PhoneWindow --|> Window
PhoneWindow --> LayoutInflater: hold
Activity --|> `LayoutInflater-Factory2`
LayoutInflater --> `LayoutInflater-Factory2`: hold

mPrivateFactory实际上是我们写的的MainActivity，所以继续会走到MainActivity.onCreateView

// androidx.fragment.app.FragmentActivity
    public View onCreateView(@Nullable View parent, @NonNull String name, @NonNull Context context,
            @NonNull AttributeSet attrs) {
        final View v = dispatchFragmentsOnCreateView(parent, name, context, attrs);
        if (v == null) {
            return super.onCreateView(parent, name, context, attrs);
        }
        return v;
    }

@param View parent: xml的根布局ConstraintLayout @param String name: fragment，也就是xml-1中的fragment标签 dispatchFragmentsOnCreateView(: 会先尝试通过该方法处理fragment标签对应的View，如果有返回结果则跳过if (v == null)中的逻辑，我们这里name为framgment，所以不应该返回null。

sequenceDiagram
autonumber

participant FragmentActivity
participant FragmentController
participant Activity
participant PhoneWindow
participant LayoutInflater
participant LayoutInflater-Factory2

FragmentActivity->>FragmentActivity: onCreate begin
FragmentActivity->>FragmentController: dispatchCreate
FragmentActivity->>Activity: setContentView
Activity->>PhoneWindow: setContentView
PhoneWindow->>LayoutInflater: inflate
LayoutInflater->>LayoutInflater-Factory2: onCreateView
LayoutInflater-Factory2->>FragmentActivity: onCreateView

classDiagram

class FragmentActivity {
    - FragmentController mFragments
}
class FragmentController
class Activity {
    - Window mWindow
}
class PhoneWindow {
    - LayoutInflater mLayoutInflater
}
class LayoutInflater
class `LayoutInflater-Factory2`

FragmentActivity --> FragmentController: hold
FragmentActivity --|> Activity
Activity --> Window: hold
PhoneWindow --|> Window
PhoneWindow --> LayoutInflater: hold
Activity --|> `LayoutInflater-Factory2`
LayoutInflater --> `LayoutInflater-Factory2`: hold

// androidx.fragment.app.FragmentActivity
    @Nullable
    final View dispatchFragmentsOnCreateView(@Nullable View parent, @NonNull String name,
            @NonNull Context context, @NonNull AttributeSet attrs) {
        return mFragments.onCreateView(parent, name, context, attrs);

sequenceDiagram
autonumber

participant FragmentActivity
participant FragmentController
participant Activity
participant PhoneWindow
participant LayoutInflater
participant LayoutInflater-Factory2

FragmentActivity->>FragmentActivity: onCreate begin
FragmentActivity->>FragmentController: dispatchCreate
FragmentActivity->>Activity: setContentView
Activity->>PhoneWindow: setContentView
PhoneWindow->>LayoutInflater: inflate
LayoutInflater->>LayoutInflater-Factory2: onCreateView
LayoutInflater-Factory2->>FragmentActivity: onCreateView
FragmentActivity->>FragmentController: onCreateView

// androidx.fragment.app.FragmentController
    public View onCreateView(@Nullable View parent, @NonNull String name, @NonNull Context context,
            @NonNull AttributeSet attrs) {
        return mHost.mFragmentManager.getLayoutInflaterFactory()
                .onCreateView(parent, name, context, attrs);
    }

sequenceDiagram
autonumber

participant FragmentActivity
participant FragmentController
participant Activity
participant PhoneWindow
participant LayoutInflater
participant LayoutInflater-Factory2
participant FragmentLayoutInflaterFactory

FragmentActivity->>FragmentActivity: onCreate begin
FragmentActivity->>FragmentController: dispatchCreate
FragmentActivity->>Activity: setContentView
Activity->>PhoneWindow: setContentView
PhoneWindow->>LayoutInflater: inflate
LayoutInflater->>LayoutInflater-Factory2: onCreateView
LayoutInflater-Factory2->>FragmentActivity: onCreateView
FragmentActivity->>FragmentController: onCreateView
FragmentController->>FragmentLayoutInflaterFactory: onCreateView

classDiagram

class FragmentActivity {
    - FragmentController mFragments
}
class FragmentController {
    FragmentHostCallback<?> mHost
}
class Activity {
    - Window mWindow
}
class PhoneWindow {
    - LayoutInflater mLayoutInflater
}
class LayoutInflater
class `LayoutInflater-Factory2`
class FragmentManager {
    FragmentLayoutInflaterFactory mLayoutInflaterFactory
}
class FragmentHostCallback {
    <<abstract>>
    FragmentManager mFragmentManager
}
class FragmentLayoutInflaterFactory

FragmentActivity --> FragmentController: hold
FragmentActivity --|> Activity
Activity --> Window: hold
PhoneWindow --|> Window
PhoneWindow --> LayoutInflater: hold
Activity --|> `LayoutInflater-Factory2`
LayoutInflater --> `LayoutInflater-Factory2`: hold
FragmentController --> FragmentHostCallback: hold
FragmentHostCallback --> FragmentManager: hold
FragmentManager --> FragmentLayoutInflaterFactory: hold

return FragmentActivity.dispatchFragmentsOnCreateView $\rightarrow$ return FragmentController.onCreateView $\rightarrow$ return FragmentLayoutInflaterFactory.onCreateView

// androidx.fragment.app.FragmentLayoutInflaterFactory
    public View onCreateView(@Nullable final View parent, @NonNull String name,
        ...
            // new Fragment
            fragment = mFragmentManager.getFragmentFactory().instantiate(
            context.getClassLoader(), fname);
            // fragment 的属性设置 begin
            fragment.mFromLayout = true;
            fragment.mFragmentId = id != 0 ? id : containerId;
            fragment.mContainerId = containerId;
            fragment.mTag = tag;
            fragment.mInLayout = true;
            fragment.mFragmentManager = mFragmentManager;
            fragment.mHost = mFragmentManager.getHost();
            fragment.onInflate(mFragmentManager.getHost().getContext(), attrs,
                    fragment.mSavedFragmentState);
            // fragment 的属性设置 end

            // 添加到mFragmentManager中，同时返回 持有Fragment的FragmentStateManager
            fragmentStateManager = mFragmentManager.addFragment(fragment);
            // 此时Fragment这个壳已经初始化，但是Fragment.mView实际上还没有构造
        ...
        // 通过FragmentStateManager更新他持有的一对一的Fragment的State
   [:1:0:0:1] fragmentStateManager.moveToExpectedState();
        // 确保走到这行代码是Fragment已经构造好view
   [B2] fragmentStateManager.ensureInflatedView();

sequenceDiagram
autonumber

participant FragmentActivity
participant FragmentController
participant Activity
participant PhoneWindow
participant LayoutInflater
participant LayoutInflater-Factory2
participant FragmentLayoutInflaterFactory
participant Fragment
participant FragmentStateManager

FragmentActivity->>FragmentActivity: onCreate begin
FragmentActivity->>FragmentController: dispatchCreate
FragmentActivity->>Activity: setContentView
Activity->>PhoneWindow: setContentView
PhoneWindow->>LayoutInflater: inflate
LayoutInflater->>LayoutInflater-Factory2: onCreateView
LayoutInflater-Factory2->>FragmentActivity: onCreateView
FragmentActivity->>FragmentController: onCreateView
FragmentController->>FragmentLayoutInflaterFactory: onCreateView
FragmentLayoutInflaterFactory->>Fragment: new
FragmentLayoutInflaterFactory->>FragmentManager: addFragment
FragmentManager->>FragmentLayoutInflaterFactory: addFragment return FragmentStateManager
FragmentLayoutInflaterFactory->>FragmentStateManager: moveToExpectedState

classDiagram

class FragmentActivity {
    - FragmentController mFragments
}
class FragmentController {
    FragmentHostCallback<?> mHost
}
class Activity {
    - Window mWindow
}
class PhoneWindow {
    - LayoutInflater mLayoutInflater
}
class LayoutInflater
class `LayoutInflater-Factory2`
class FragmentManager {
    FragmentLayoutInflaterFactory mLayoutInflaterFactory
}
class FragmentHostCallback {
    <<abstract>>
    FragmentManager mFragmentManager
}
class FragmentLayoutInflaterFactory {
    FragmentManager mFragmentManager
}

FragmentActivity --> FragmentController: hold
FragmentActivity --|> Activity
Activity --> Window: hold
PhoneWindow --|> Window
PhoneWindow --> LayoutInflater: hold
Activity --|> `LayoutInflater-Factory2`
LayoutInflater --> `LayoutInflater-Factory2`: hold
FragmentController --> FragmentHostCallback: hold
FragmentHostCallback --> FragmentManager: hold
FragmentManager --> FragmentLayoutInflaterFactory: hold
FragmentLayoutInflaterFactory --> FragmentManager: ref

fragmentStateManager = mFragmentManager.addFragment(fragment);: 将新建的Fragment添加到FragmentManager中进行管理。

[:1:0:0:1] fragmentStateManager.moveToExpectedState(); 通过FragmentStateManager更新他持有的一对一的Fragment的State

// androidx.fragment.app.FragmentStateManager
    void moveToExpectedState() {
        ...
            int newState;
     [:1:0:0:1:0] while ((newState = computeExpectedState()) != mFragment.mState) {
                if (newState > mFragment.mState) {
                    // Moving upward
                    int nextStep = mFragment.mState + 1;
                    switch (nextStep) {
                        case Fragment.ATTACHED:
                     [:1:0:0:1:1] attach();
                        case Fragment.CREATED:
                     [:1:0:0:1:2] create();
                            break;
                        case Fragment.VIEW_CREATED:
                     [:1:0:0:1:3] ensureInflatedView();
                     [:1:0:0:1:4] createView();
                            break;

[:1:0:0:1:0] while ((newState = computeExpectedState()) != mFragment.mState) {

computeExpectedState(): 根据FragmentManager等等计算mFragment应该达到的状态，先不看这里的复杂计算，但是最终的结果是2，对应Fragment.VIEW_CREATED，即Fragment应该进行到构造好View的状态
while: mFragment不断切换到下一个状态，直到达到目标状态——VIEW_CREATED
mFragment.mState: 当前mFragment.mState为INITIALIZING，则表示会依次执行FragmentManager.attach()、FragmentManager.create()、FragmentManager.createView()

    static final int INITIALIZING = -1;          // Not yet attached.
    static final int ATTACHED = 0;               // Attached to the host.
    static final int CREATED = 1;                // Created.
    static final int VIEW_CREATED = 2;           // View Created.
    static final int AWAITING_EXIT_EFFECTS = 3;  // Downward state, awaiting exit effects
    static final int ACTIVITY_CREATED = 4;       // Fully created, not started.
    static final int STARTED = 5;                // Created and started, not resumed.
    static final int AWAITING_ENTER_EFFECTS = 6; // Upward state, awaiting enter effects
    static final int RESUMED = 7;                // Created started and resumed.

[:1:0:0:1:1] attach();

// androidx.fragment.app.FragmentStateManager
    void attach() {
        ....
[:1:0:0:1:1:0] mFragment.performAttach();
        mDispatcher.dispatchOnFragmentAttached(mFragment, false);
    }

sequenceDiagram
autonumber

participant FragmentActivity
participant FragmentController
participant Activity
participant PhoneWindow
participant LayoutInflater
participant LayoutInflater-Factory2
participant FragmentLayoutInflaterFactory
participant Fragment
participant FragmentStateManager

FragmentActivity->>FragmentActivity: onCreate begin
FragmentActivity->>FragmentController: dispatchCreate
FragmentActivity->>Activity: setContentView
Activity->>PhoneWindow: setContentView
PhoneWindow->>LayoutInflater: inflate
LayoutInflater->>LayoutInflater-Factory2: onCreateView
LayoutInflater-Factory2->>FragmentActivity: onCreateView
FragmentActivity->>FragmentController: onCreateView
FragmentController->>FragmentLayoutInflaterFactory: onCreateView
FragmentLayoutInflaterFactory->>Fragment: new
FragmentLayoutInflaterFactory->>FragmentManager: addFragment
FragmentManager->>FragmentLayoutInflaterFactory: addFragment return FragmentStateManager
FragmentLayoutInflaterFactory->>FragmentStateManager: moveToExpectedState
FragmentStateManager->>Fragment: performAttach

[:1:0:0:1:1:0] mFragment.performAttach()

// androidx.fragment.app.Fragment
    void performAttach() {
        ...
        mState = ATTACHED;
        onAttach(mHost.getContext());
        ...
        mChildFragmentManager.dispatchAttach();
    }

mState = ATTACHED: 更新Fragment状态为ATTACHED

// androidx.fragment.app.Fragment
    public void onAttach(@NonNull Context context) {
        mCalled = true;
        final Activity hostActivity = mHost == null ? null : mHost.getActivity();
        if (hostActivity != null) {
            mCalled = false;
            onAttach(hostActivity);
        }
    }

// androidx.fragment.app.Fragment
    public void onAttach(@NonNull Activity activity) {
        mCalled = true;
    }

至此，Fragment的状态由INITIALIZING切换到ATTACHED切换到CREATED切换到VIEW_CREATED，关键方法是B1-fragmentStateManager.moveToExpectedState，不断的将FragmentStateManager所管理的所有Fragment推动到应该达到的状态。

sequenceDiagram
autonumber

participant FragmentActivity
participant FragmentManager
participant Fragment

activate FragmentActivity
FragmentActivity->>FragmentActivity: onCreate begin
FragmentActivity->>FragmentManager: dispatchCreate() 分发CREATE
FragmentActivity->>FragmentActivity: setContentView begin
FragmentActivity->>FragmentActivity: onCreateView
FragmentActivity->>FragmentManager: moveToExpectedState
FragmentManager->>Fragment: performAttach
Fragment->>Fragment: onAttach
FragmentManager->>Fragment: performCreate
FragmentManager->>Fragment: performCreateView

FragmentActivity->>FragmentActivity: onCreate end 
deactivate FragmentActivity

FragmentActivity->>FragmentActivity: onStart

以上以Create为例，了解了FragmentActivity的状态对Fragment的状态影响以及FragmentActivity, FragmentController, FragmentManager, FragmentStateManager, Fragment中间的关系。

MainActivity onCreate
MainActivity onCreateView 2
MainActivity onCreateView 1
MainActivity onCreateView 2
MainActivity onCreateView 1
MainActivity onCreateView 2
MainActivity onCreateView 1
MainActivity onCreateView 2
MainActivity onCreateView 1
MainActivity onCreateView 2
MainActivity onCreateView 1
MainActivity onCreateView 2
fragment 1 onAttach
MainActivity onAttachFragment
fragment 1 onCreate
fragment 1 onCreateView
fragment 1 onViewCreated
MainActivity onCreateView 2
MainActivity onCreateView 1
MainActivity onCreate end
MainActivity onStart begin
fragment 1 onActivityCreated
fragment 1 onStart
MainActivity onStart end
MainActivity onResume
fragment 1 onResumek

简单总结：

Activity 生命周期回调	Fragment 生命周期回调
onCreate	- onAttach - onCreate - onCreateView - onViewCreated
onStart	- onActivityCreated - onStart
onResume	- onResume

总结

总结以上，FragmentActivity onCreate 时将 Create 事件 $\xrightarrow{1:通知:1}$ FragmentController $\xrightarrow{1:通知:1}$ FragmentManager $\xrightarrow{1:通知:n}$ 持有的每个 FragmentStateManager $\xrightarrow{1:通知:1}$ Fragment。

代码中动态添加Fragment

// MainActivity
    private fun f1() {
        f1?.setOnClickListener {
       [:2] val transaction = supportFragmentManager.beginTransaction()
       [:3] transaction.add(R.id.content_fragment, Fragment2())
       [:4] transaction.commit()
        }
    }

[:2] val transaction = supportFragmentManager.beginTransaction()

// androidx.fragment.app.FragmentManager
    public FragmentTransaction beginTransaction() {
        return new BackStackRecord(this);
    }

sequenceDiagram
autonumber

participant MainActivity
participant FragmentManager
participant FragmentTransaction
participant BackStackRecord

MainActivity ->> FragmentManager: beginTransaction
FragmentManager ->> FragmentTransaction: new
FragmentManager ->> BackStackRecord: new
FragmentManager ->> MainActivity: return (FragmentTransaction)BackStackRecord

classDiagram
class FragmentTransaction
class BackStackRecord
class FragmentManager
class `FragmentManager-BackStackEntry`
class `FragmentManager-OpGenerator`

BackStackRecord --|> FragmentTransaction: extends
BackStackRecord --|> `FragmentManager-BackStackEntry`: impl
BackStackRecord --|>` FragmentManager-OpGenerator`: impl
FragmentManager --> BackStackRecord: create

[:3] transaction.add(R.id.content_fragment, Fragment2())

// androidx.fragment.app.FragmentTransaction
    public FragmentTransaction add(@IdRes int containerViewId, @NonNull Fragment fragment) {
   [:3:0] doAddOp(containerViewId, fragment, null, OP_ADD);
        return this;
    }

sequenceDiagram
autonumber

participant MainActivity
participant FragmentManager
participant FragmentTransaction
participant BackStackRecord

MainActivity ->> FragmentManager: beginTransaction
FragmentManager ->> FragmentTransaction: new
FragmentManager ->> BackStackRecord: new
FragmentManager ->> MainActivity: return (FragmentTransaction)BackStackRecord
MainActivity ->> FragmentTransaction: add

其中OP_ADD⬇️ = 1

// androidx.fragment.app.FragmentTransaction
    static final int OP_NULL = 0;
    static final int OP_ADD = 1;
    static final int OP_REPLACE = 2;
    static final int OP_REMOVE = 3;
    static final int OP_HIDE = 4;
    static final int OP_SHOW = 5;
    static final int OP_DETACH = 6;
    static final int OP_ATTACH = 7;
    static final int OP_SET_PRIMARY_NAV = 8;
    static final int OP_UNSET_PRIMARY_NAV = 9;
    static final int OP_SET_MAX_LIFECYCLE = 10;

[:3:0] doAddOp(containerViewId, fragment, null, OP_ADD)

// androidx.fragment.app.FragmentTransaction
    void doAddOp(int containerViewId, Fragment fragment, @Nullable String tag, int opcmd) {
        ...
   [:3:0:1] addOp(new Op(opcmd, fragment));
    }

[:3:0:1] addOp(new Op(opcmd, fragment))

// androidx.fragment.app.FragmentTransaction
    void addOp(Op op) {
        mOps.add(op);
        ...
    }

// androidx.fragment.app.FragmentTransaction
    ArrayList<Op> mOps = new ArrayList<>();

classDiagram
class FragmentTransaction {
    mOps: ArrayList<OP>
}
class BackStackRecord
class FragmentManager
class `FragmentManager-BackStackEntry`
class `FragmentManager-OpGenerator`
class `FragmentTransaction-Op` {
    mCmd: int
    mFragment: Fragment
}

BackStackRecord --|> FragmentTransaction: extends
BackStackRecord --|> `FragmentManager-BackStackEntry`: impl
BackStackRecord --|> `FragmentManager-OpGenerator`: impl
FragmentManager --> BackStackRecord: create
FragmentTransaction --> `FragmentTransaction-Op`: holds

FragmentTransaction 中有一个 Op list记录我们添加的操作——OP_ADD

[:4] transaction.commit()

// androidx.fragment.app.FragmentTransaction
    public abstract int commit();

sequenceDiagram
autonumber

participant MainActivity
participant FragmentManager
participant FragmentTransaction
participant BackStackRecord

MainActivity ->> FragmentManager: beginTransaction
FragmentManager ->> FragmentTransaction: new
FragmentManager ->> BackStackRecord: new
FragmentManager ->> MainActivity: return (FragmentTransaction)BackStackRecord
MainActivity ->> FragmentTransaction: add
MainActivity ->> FragmentTransaction: commit

// androidx.fragment.app.BackStackRecord
    @Override
    public int commit() {
        return commitInternal(false);
    }

    // androidx.fragment.app.BackStackRecord
    int commitInternal(boolean allowStateLoss) {
        ...
    [:4:0] mManager.enqueueAction(this, allowStateLoss);
        ...
    }

sequenceDiagram
autonumber

participant MainActivity
participant FragmentManager
participant FragmentTransaction
participant BackStackRecord

MainActivity ->> FragmentManager: beginTransaction
FragmentManager ->> FragmentTransaction: new
FragmentManager ->> BackStackRecord: new
FragmentManager ->> MainActivity: return (FragmentTransaction)BackStackRecord
MainActivity ->> FragmentTransaction: add
MainActivity ->> FragmentTransaction: commit
FragmentTransaction ->> FragmentManager: enqueueAction

[:4:0] mManager.enqueueAction(this, allowStateLoss);

// androidx.fragment.app.FragmentManager
    void enqueueAction(@NonNull OpGenerator action, boolean allowStateLoss) {
        ...
            mPendingActions.add(action);
   [:4:0:0] scheduleCommit();
        ...
    }

// androidx.fragment.app.FragmentManager
    private final ArrayList<OpGenerator> mPendingActions = new ArrayList<>();

// androidx.fragment.app.FragmentManager
    interface OpGenerator {
        /**
         * Generate transactions to add to {@code records} and whether or not the transaction is
         * an add or pop to {@code isRecordPop}.
         *
         * records and isRecordPop must be added equally so that each transaction in records
         * matches the boolean for whether or not it is a pop in isRecordPop.
         *
         * @param records A list to add transactions to.
         * @param isRecordPop A list to add whether or not the transactions added to records is
         *                    a pop transaction.
         * @return true if something was added or false otherwise.
         */
        boolean generateOps(@NonNull ArrayList<BackStackRecord> records,
                @NonNull ArrayList<Boolean> isRecordPop);
    }

sequenceDiagram
autonumber

participant MainActivity
participant FragmentManager
participant FragmentTransaction
participant BackStackRecord

MainActivity ->> FragmentManager: beginTransaction
FragmentManager ->> FragmentTransaction: new
FragmentManager ->> BackStackRecord: new
FragmentManager ->> MainActivity: return (FragmentTransaction)BackStackRecord
MainActivity ->> FragmentTransaction: add
MainActivity ->> FragmentTransaction: commit
FragmentTransaction ->> FragmentManager: enqueueAction
FragmentManager ->> FragmentManager: mPendingActions.add

classDiagram
class FragmentTransaction {
    mOps: ArrayList"OP"
}
class BackStackRecord
class FragmentManager {
    mPendingActions: ArrayList"OpGenerator"
}
class `FragmentManager-BackStackEntry`
class `FragmentManager-OpGenerator`
class `FragmentTransaction-Op` {
    mCmd: int
    mFragment: Fragment
}

BackStackRecord --|> FragmentTransaction: extends
BackStackRecord --|> `FragmentManager-BackStackEntry`: impl
BackStackRecord --|> `FragmentManager-OpGenerator`: impl
FragmentManager --> BackStackRecord: create
FragmentTransaction --> `FragmentTransaction-Op`: holds
FragmentManager --> `FragmentManager-OpGenerator`: holds

[:4:0:0] scheduleCommit();

// androidx.fragment.app.FragmentManager
    void scheduleCommit() {
        synchronized (mPendingActions) {
                ...
      [:4:0:0:0] mHost.getHandler().post(mExecCommit);
                ...
    }

sequenceDiagram
autonumber

participant MainActivity
participant FragmentManager
participant FragmentTransaction
participant BackStackRecord

MainActivity ->> FragmentManager: beginTransaction
FragmentManager ->> FragmentTransaction: new
FragmentManager ->> BackStackRecord: new
FragmentManager ->> MainActivity: return (FragmentTransaction)BackStackRecord
MainActivity ->> FragmentTransaction: add
MainActivity ->> FragmentTransaction: commit
FragmentTransaction ->> FragmentManager: enqueueAction
FragmentManager ->> FragmentManager: mPendingActions.add
FragmentManager ->> FragmentManager: scheduleCommit

[:4:0:0:0] mHost.getHandler().post(mExecCommit)
mExecCommit ⬇️被放入消息队列，之后会被执行。

    // androidx.fragment.app.FragmentManager
    private Runnable mExecCommit = new Runnable() {
        @Override
        public void run() {
  [:4:0:0:0:0] execPendjingActions(true);
        }
    };

[:4:0:0:0:0] execPendjingActions(true);

    // androidx.fragment.app.FragmentManager
    boolean execPendingActions(boolean allowStateLoss) {
        ensureExecReady(allowStateLoss);

[:4:0:0:0:0:0]while (generateOpsForPendingActions(mTmpRecords, mTmpIsPop)) {
            mExecutingActions = true;
            try {
 [:4:0:0:0:0:1] removeRedundantOperationsAndExecute(mTmpRecords, mTmpIsPop);
                ...

sequenceDiagram
autonumber

participant MainActivity
participant FragmentManager
participant FragmentTransaction
participant BackStackRecord

MainActivity ->> FragmentManager: beginTransaction
FragmentManager ->> FragmentTransaction: new
FragmentManager ->> BackStackRecord: new
FragmentManager ->> MainActivity: return (FragmentTransaction)BackStackRecord
MainActivity ->> FragmentTransaction: add
MainActivity ->> FragmentTransaction: commit
FragmentTransaction ->> FragmentManager: enqueueAction
FragmentManager ->> FragmentManager: mPendingActions.add
FragmentManager ->> FragmentManager: scheduleCommit
FragmentManager ->> FragmentManager: execPendingActions

[:4:0:0:0:0:0] generateOpsForPendingActions(mTmpRecords, mTmpIsPop)

    // androidx.fragment.app.FragmentManager
    private boolean generateOpsForPendingActions(@NonNull ArrayList<BackStackRecord> records,
            @NonNull ArrayList<Boolean> isPop) {
            ...
            for (int i = 0; i < numActions; i++) {
  [:4:0:0:0:0:0:0] didSomething |= mPendingActions.get(i).generateOps(records, isPop);
            }
            ...
    }

这里对mPendingActions中的每一个Action都调用generateOps——会处理到之前在[:4:0]添加的Action

sequenceDiagram
autonumber

participant MainActivity
participant FragmentManager
participant FragmentTransaction
participant BackStackRecord
participant OpGenerator

MainActivity ->> FragmentManager: beginTransaction
FragmentManager ->> FragmentTransaction: new
FragmentManager ->> BackStackRecord: new
FragmentManager ->> MainActivity: return (FragmentTransaction)BackStackRecord
MainActivity ->> FragmentTransaction: add
MainActivity ->> FragmentTransaction: commit
FragmentTransaction ->> FragmentManager: enqueueAction
FragmentManager ->> FragmentManager: mPendingActions.add
FragmentManager ->> FragmentManager: scheduleCommit
FragmentManager ->> FragmentManager: execPendingActions
FragmentManager ->> OpGenerator: generateOps
OpGenerator ->> BackStackRecord: generateOps

classDiagram
class FragmentTransaction {
    mOps: ArrayList"OP"
}
class BackStackRecord
class FragmentManager {
    mPendingActions: ArrayList"OpGenerator"
}
class `FragmentManager-BackStackEntry`
class `FragmentManager-OpGenerator` {
    boolean generateOps()
}
class `FragmentTransaction-Op` {
    mCmd: int
    mFragment: Fragment
}

BackStackRecord --|> FragmentTransaction: extends
BackStackRecord --|> `FragmentManager-BackStackEntry`: impl
BackStackRecord --|> `FragmentManager-OpGenerator`: impl
FragmentManager --> BackStackRecord: create
FragmentTransaction --> `FragmentTransaction-Op`: holds
FragmentManager --> `FragmentManager-OpGenerator`: holds

[:4:0:0:0:0:0:0] mPendingActions.get(i).generateOps(records, isPop)

    // androidx.fragment.app.BackStackRecord
    public boolean generateOps(@NonNull ArrayList<BackStackRecord> records,
            @NonNull ArrayList<Boolean> isRecordPop) {

        ...
        records.add(this);
        ...
    }

BackStackRecord将自己添加到传入的records中

[:4:0:0:0:0:1] removeRedundantOperationsAndExecute(mTmpRecords, mTmpIsPop)
遍历[:4:0:0:0:0:0]返回的每一个record，对其处理

    // androidx.fragment.app.FragmentManager
    private void removeRedundantOperationsAndExecute(@NonNull ArrayList<BackStackRecord> records,
            @NonNull ArrayList<Boolean> isRecordPop) {
        ...
        final int numRecords = records.size();

        for (int recordNum = 0; recordNum < numRecords; recordNum++) {
            ...
                   int reorderingEnd = recordNum + 1;
  [:4:0:0:0:0:1:0] executeOpsTogether(records, isRecordPop, recordNum, reorderingEnd);
            ...
        }
    }

遍历执行record，executeOpsTogether(records传入了整个records——只有一个OP_ADD，通过后面两个参数指定要执行的 record的开始位置和结束位置——recordNum(0)和reorderingEnd(recordNum + 1 = 0 + 1 = 1)，也就相当于挨个执行。

sequenceDiagram
autonumber

participant MainActivity
participant FragmentManager
participant FragmentTransaction
participant BackStackRecord
participant OpGenerator

MainActivity ->> FragmentManager: beginTransaction
FragmentManager ->> FragmentTransaction: new
FragmentManager ->> BackStackRecord: new
FragmentManager ->> MainActivity: return (FragmentTransaction)BackStackRecord
MainActivity ->> FragmentTransaction: add
MainActivity ->> FragmentTransaction: commit
FragmentTransaction ->> FragmentManager: enqueueAction
FragmentManager ->> FragmentManager: mPendingActions.add
FragmentManager ->> FragmentManager: scheduleCommit
FragmentManager ->> FragmentManager: execPendingActions
FragmentManager ->> OpGenerator: generateOps
OpGenerator ->> BackStackRecord: generateOps
FragmentManager ->> FragmentManager: removeRedundantOperationsAndExecute

[:4:0:0:0:0:1:0] executeOpsTogether(records, isRecordPop, recordNum, reorderingEnd)

    // androidx.fragment.app.FragmentManager
    private void executeOpsTogether(@NonNull ArrayList<BackStackRecord> records,
            @NonNull ArrayList<Boolean> isRecordPop, int startIndex, int endIndex) {
        ...
[:4:0:0:0:0:1:0:0] executeOps(records, isRecordPop, startIndex, endIndex);
        ...
         [:4:0:0:0:0:1:0:1] fragmentStateManager.moveToExpectedState();
        ...
        
        ...

startIndex: recordNum = 0
endIndex: reorderingEnd = 1

[:4:0:0:0:0:1:0:0] executeOps(records, isRecordPop, startIndex, endIndex);

    // androidx.fragment.app.FragmentManager
    private static void executeOps(@NonNull ArrayList<BackStackRecord> records,
        @NonNull ArrayList<Boolean> isRecordPop, int startIndex, int endIndex) {
        for (int i = startIndex; i < endIndex; i++) {
 [:4:0:0:0:0:1:0:0:0] record.executeOps();
            }
        }
    }

sequenceDiagram
autonumber

participant MainActivity
participant FragmentManager
participant FragmentTransaction
participant BackStackRecord
participant OpGenerator

MainActivity ->> FragmentManager: beginTransaction
FragmentManager ->> FragmentTransaction: new
FragmentManager ->> BackStackRecord: new
FragmentManager ->> MainActivity: return (FragmentTransaction)BackStackRecord
MainActivity ->> FragmentTransaction: add
MainActivity ->> FragmentTransaction: commit
FragmentTransaction ->> FragmentManager: enqueueAction
FragmentManager ->> FragmentManager: mPendingActions.add
FragmentManager ->> FragmentManager: scheduleCommit
FragmentManager ->> FragmentManager: execPendingActions
FragmentManager ->> OpGenerator: generateOps
OpGenerator ->> BackStackRecord: generateOps
FragmentManager ->> FragmentManager: removeRedundantOperationsAndExecute
FragmentManager ->> FragmentManager: executeOpsTogether
FragmentManager ->> FragmentManager: executeOps
FragmentManager ->> BackStackRecord: executeOps

classDiagram
class FragmentTransaction {
    mOps: ArrayList"OP"
}
class BackStackRecord {
    executeOps(): void
}
class FragmentManager {
    mPendingActions: ArrayList"OpGenerator"
}
class `FragmentManager-BackStackEntry`
class `FragmentManager-OpGenerator` {
    boolean generateOps()
}
class `FragmentTransaction-Op` {
    mCmd: int
    mFragment: Fragment
}

BackStackRecord --|> FragmentTransaction: extends
BackStackRecord --|> `FragmentManager-BackStackEntry`: impl
BackStackRecord --|> `FragmentManager-OpGenerator`: impl
FragmentManager --> BackStackRecord: create
FragmentTransaction --> `FragmentTransaction-Op`: holds
FragmentManager --> `FragmentManager-OpGenerator`: holds

[:4:0:0:0:0:1:0:0:0] record.executeOps();

    // androidx.fragment.app.BackStackRecord
    void executeOps() {
        final int numOps = mOps.size();
        for (int opNum = 0; opNum < numOps; opNum++) {
            switch (op.mCmd) {
                case OP_ADD:
                    f.setAnimations(op.mEnterAnim, op.mExitAnim, op.mPopEnterAnim, op.mPopExitAnim);
                    mManager.setExitAnimationOrder(f, false);
[:4:0:0:0:0:1:0:0:0:0] mManager.addFragment(f);
                    break;

mOps的数量为1——[:3:0:1] 添加的OP_ADD

sequenceDiagram
autonumber

participant MainActivity
participant FragmentManager
participant FragmentTransaction
participant BackStackRecord
participant OpGenerator

MainActivity ->> FragmentManager: beginTransaction
FragmentManager ->> FragmentTransaction: new
FragmentManager ->> BackStackRecord: new
FragmentManager ->> MainActivity: return (FragmentTransaction)BackStackRecord
MainActivity ->> FragmentTransaction: add
MainActivity ->> FragmentTransaction: commit
FragmentTransaction ->> FragmentManager: enqueueAction
FragmentManager ->> FragmentManager: mPendingActions.add
FragmentManager ->> FragmentManager: scheduleCommit
FragmentManager ->> FragmentManager: execPendingActions
FragmentManager ->> OpGenerator: generateOps
OpGenerator ->> BackStackRecord: generateOps
FragmentManager ->> FragmentManager: removeRedundantOperationsAndExecute
FragmentManager ->> FragmentManager: executeOpsTogether
FragmentManager ->> FragmentManager: executeOps
FragmentManager ->> BackStackRecord: executeOps
BackStackRecord ->> FragmentManager: addFragment

[:4:0:0:0:0:1:0:0:0:0] mManager.addFragment(f);

    // androidx.fragment.app.FragmentManager
    FragmentStateManager addFragment(@NonNull Fragment fragment) {
        if (isLoggingEnabled(Log.VERBOSE)) Log.v(TAG, "add: " + fragment);
        FragmentStateManager fragmentStateManager = createOrGetFragmentStateManager(fragment);
        fragment.mFragmentManager = this;
        mFragmentStore.makeActive(fragmentStateManager);
        if (!fragment.mDetached) {
            mFragmentStore.addFragment(fragment);
            fragment.mRemoving = false;
            if (fragment.mView == null) {
                fragment.mHiddenChanged = false;
            }
            if (isMenuAvailable(fragment)) {
                mNeedMenuInvalidate = true;
            }
        }
        return fragmentStateManager;
    }

[:4:0:0:0:0:1:0:1] fragmentStateManager.moveToExpectedState()
这里回到上面说过的 [:1:0:0:1]

Fragment原理

Activity的生命周期与Fragment生命周期的关联

示例代码

通过xml文件添加Fragment —— Fragment1

关键节点 [:0] FragmentActivity.onCreate

关键节点 [:1] setContentView(R.layout.activity_main)

总结

代码中动态添加Fragment

参考