一、Fragment
1.1 生命周期
官方网上的Fragment声明周期。
图 1 Fragment生命周期流程图
除了上述声明周期之外，也可以注册FragmentLifecycleCallbacks来插入更多Fragment状态的监听，具体有：
public abstract static class FragmentLifecycleCallbacks {
/**
* Called right before the fragment's {@link Fragment#onAttach(Context)} method is called.
* This is a good time to inject any required dependencies or perform other configuration
* for the fragment before any of the fragment's lifecycle methods are invoked.
*
* @param fm Host FragmentManager
* @param f Fragment changing state
* @param context Context that the Fragment is being attached to
*/
public void onFragmentPreAttached(@NonNull FragmentManager fm, @NonNull Fragment f,
@NonNull Context context) {}
/**
* Called after the fragment has been attached to its host. Its host will have had
* <code>onAttachFragment</code> called before this call happens.
*
* @param fm Host FragmentManager
* @param f Fragment changing state
* @param context Context that the Fragment was attached to
*/
public void onFragmentAttached(@NonNull FragmentManager fm, @NonNull Fragment f,
@NonNull Context context) {}
/**
* Called right before the fragment's {@link Fragment#onCreate(Bundle)} method is called.
* This is a good time to inject any required dependencies or perform other configuration
* for the fragment.
*
* @param fm Host FragmentManager
* @param f Fragment changing state
* @param savedInstanceState Saved instance bundle from a previous instance
*/
public void onFragmentPreCreated(@NonNull FragmentManager fm, @NonNull Fragment f,
@Nullable Bundle savedInstanceState) {}
/**
* Called after the fragment has returned from the FragmentManager's call to
* {@link Fragment#onCreate(Bundle)}. This will only happen once for any given
* fragment instance, though the fragment may be attached and detached multiple times.
*
* @param fm Host FragmentManager
* @param f Fragment changing state
* @param savedInstanceState Saved instance bundle from a previous instance
*/
public void onFragmentCreated(@NonNull FragmentManager fm, @NonNull Fragment f,
@Nullable Bundle savedInstanceState) {}
/**
* Called after the fragment has returned from the FragmentManager's call to
* {@link Fragment#onActivityCreated(Bundle)}. This will only happen once for any given
* fragment instance, though the fragment may be attached and detached multiple times.
*
* @param fm Host FragmentManager
* @param f Fragment changing state
* @param savedInstanceState Saved instance bundle from a previous instance
*/
public void onFragmentActivityCreated(@NonNull FragmentManager fm, @NonNull Fragment f,
@Nullable Bundle savedInstanceState) {}
/**
* Called after the fragment has returned a non-null view from the FragmentManager's
* request to {@link Fragment#onCreateView(LayoutInflater, ViewGroup, Bundle)}.
*
* @param fm Host FragmentManager
* @param f Fragment that created and owns the view
* @param v View returned by the fragment
* @param savedInstanceState Saved instance bundle from a previous instance
*/
public void onFragmentViewCreated(@NonNull FragmentManager fm, @NonNull Fragment f,
@NonNull View v, @Nullable Bundle savedInstanceState) {}
/**
* Called after the fragment has returned from the FragmentManager's call to
* {@link Fragment#onStart()}.
*
* @param fm Host FragmentManager
* @param f Fragment changing state
*/
public void onFragmentStarted(@NonNull FragmentManager fm, @NonNull Fragment f) {}
/**
* Called after the fragment has returned from the FragmentManager's call to
* {@link Fragment#onResume()}.
*
* @param fm Host FragmentManager
* @param f Fragment changing state
*/
public void onFragmentResumed(@NonNull FragmentManager fm, @NonNull Fragment f) {}
/**
* Called after the fragment has returned from the FragmentManager's call to
* {@link Fragment#onPause()}.
*
* @param fm Host FragmentManager
* @param f Fragment changing state
*/
public void onFragmentPaused(@NonNull FragmentManager fm, @NonNull Fragment f) {}
/**
* Called after the fragment has returned from the FragmentManager's call to
* {@link Fragment#onStop()}.
*
* @param fm Host FragmentManager
* @param f Fragment changing state
*/
public void onFragmentStopped(@NonNull FragmentManager fm, @NonNull Fragment f) {}
/**
* Called after the fragment has returned from the FragmentManager's call to
* {@link Fragment#onSaveInstanceState(Bundle)}.
*
* @param fm Host FragmentManager
* @param f Fragment changing state
* @param outState Saved state bundle for the fragment
*/
public void onFragmentSaveInstanceState(@NonNull FragmentManager fm, @NonNull Fragment f,
@NonNull Bundle outState) {}
/**
* Called after the fragment has returned from the FragmentManager's call to
* {@link Fragment#onDestroyView()}.
*
* @param fm Host FragmentManager
* @param f Fragment changing state
*/
public void onFragmentViewDestroyed(@NonNull FragmentManager fm, @NonNull Fragment f) {}
/**
* Called after the fragment has returned from the FragmentManager's call to
* {@link Fragment#onDestroy()}.
*
* @param fm Host FragmentManager
* @param f Fragment changing state
*/
public void onFragmentDestroyed(@NonNull FragmentManager fm, @NonNull Fragment f) {}
/**
* Called after the fragment has returned from the FragmentManager's call to
* {@link Fragment#onDetach()}.
*
* @param fm Host FragmentManager
* @param f Fragment changing state
*/
public void onFragmentDetached(@NonNull FragmentManager fm, @NonNull Fragment f) {}
}
所以，如果考虑开发中自己注册的状态变化监听，那么其方法调用过程如下图
图 2 Fragment生命周期及FragmentLifecycleCallbacks流程图
1.2 生命周期执行顺序源码解析
1、Fragment的提交并展示
通常我们使用下列代码来提交并展示一个Fragment
XXXFragment fragment = new XXXFragment();
Bundle bundle = new Bundle();
bundle.putString("key", "value");
fragment.setAurguments(bundle);
// 或者commitAllowStateLoss
getSupportFragmentManager.beginTransaction().add(R.id.xxx, fragment).commit();
添加Fragment视图的方式有很多，例如add()、replace()
这里已add()方法为例，看下代码实现
// FragmentTransaction.java
......
/**
* Calls {@link #add(int, Fragment, String)} with a 0 containerViewId.
*/
@NonNull
public FragmentTransaction add(@NonNull Fragment fragment, @Nullable String tag) {
doAddOp(0, fragment, tag, OP_ADD);
return this;
}
......
void doAddOp(int containerViewId, Fragment fragment, @Nullable String tag, int opcmd) {
final Class<?> fragmentClass = fragment.getClass();
final int modifiers = fragmentClass.getModifiers();
if (fragmentClass.isAnonymousClass() || !Modifier.isPublic(modifiers)
|| (fragmentClass.isMemberClass() && !Modifier.isStatic(modifiers))) {
throw new IllegalStateException("Fragment " + fragmentClass.getCanonicalName()
+ " must be a public static class to be properly recreated from"
+ " instance state.");
}
if (tag != null) {
if (fragment.mTag != null && !tag.equals(fragment.mTag)) {
throw new IllegalStateException("Can't change tag of fragment "
+ fragment + ": was " + fragment.mTag
+ " now " + tag);
}
fragment.mTag = tag;
}
if (containerViewId != 0) {
if (containerViewId == View.NO_ID) {
throw new IllegalArgumentException("Can't add fragment "
+ fragment + " with tag " + tag + " to container view with no id");
}
if (fragment.mFragmentId != 0 && fragment.mFragmentId != containerViewId) {
throw new IllegalStateException("Can't change container ID of fragment "
+ fragment + ": was " + fragment.mFragmentId
+ " now " + containerViewId);
}
fragment.mContainerId = fragment.mFragmentId = containerViewId;
}
addOp(new Op(opcmd, fragment));
}
......
void addOp(Op op) {
mOps.add(op);
op.mEnterAnim = mEnterAnim;
op.mExitAnim = mExitAnim;
op.mPopEnterAnim = mPopEnterAnim;
op.mPopExitAnim = mPopExitAnim;
}
代码看似很多，其实主要目的是将OP_ADD这一指令保存在列表中，然后接着看commit()
// BackStackRecord.java
@Override
public int commit() {
return commitInternal(false);
}
int commitInternal(boolean allowStateLoss) {
if (mCommitted) throw new IllegalStateException("commit already called");
if (FragmentManagerImpl.DEBUG) {
Log.v(TAG, "Commit: " + this);
LogWriter logw = new LogWriter(TAG);
PrintWriter pw = new PrintWriter(logw);
dump(" ", pw);
pw.close();
}
mCommitted = true;
if (mAddToBackStack) {
mIndex = mManager.allocBackStackIndex(this);
} else {
mIndex = -1;
}
// ①
mManager.enqueueAction(this, allowStateLoss);
return mIndex;
}
①：将提交Fragment事件添加到执行队列中等待执行。
继续深入查看代码，mManager是FragmentManagerImpl对象，执行它的enqueueAction()方法。
// FragmentManagerImpl.java
/**
* Adds an action to the queue of pending actions.
*
* @param action the action to add
* @param allowStateLoss whether to allow loss of state information
* @throws IllegalStateException if the activity has been destroyed
*/
public void enqueueAction(OpGenerator action, boolean allowStateLoss) {
if (!allowStateLoss) {
checkStateLoss();
}
synchronized (this) {
if (mDestroyed || mHost == null) {
if (allowStateLoss) {
// This FragmentManager isn't attached, so drop the entire transaction.
return;
}
throw new IllegalStateException("Activity has been destroyed");
}
if (mPendingActions == null) {
mPendingActions = new ArrayList<>();
}
// ②
mPendingActions.add(action);
scheduleCommit();
}
}
/**
* Schedules the execution when one hasn't been scheduled already. This should happen
* the first time {@link #enqueueAction(OpGenerator, boolean)} is called or when
* a postponed transaction has been started with
* {@link Fragment#startPostponedEnterTransition()}
*/
@SuppressWarnings("WeakerAccess") /* synthetic access */
void scheduleCommit() {
synchronized (this) {
boolean postponeReady =
mPostponedTransactions != null && !mPostponedTransactions.isEmpty();
// ③
boolean pendingReady = mPendingActions != null && mPendingActions.size() == 1;
if (postponeReady || pendingReady) {
mHost.getHandler().removeCallbacks(mExecCommit);
// ④
mHost.getHandler().post(mExecCommit);
updateOnBackPressedCallbackEnabled();
}
}
}
Runnable mExecCommit = new Runnable() {
@Override
public void run() {
execPendingActions();
}
};
/**
* Only call from main thread!
*/
public boolean execPendingActions() {
ensureExecReady(true);
boolean didSomething = false;
while (generateOpsForPendingActions(mTmpRecords, mTmpIsPop)) {
mExecutingActions = true;
try {
removeRedundantOperationsAndExecute(mTmpRecords, mTmpIsPop);
} finally {
cleanupExec();
}
didSomething = true;
}
updateOnBackPressedCallbackEnabled();
doPendingDeferredStart();
burpActive();
return didSomething;
}
private void removeRedundantOperationsAndExecute(ArrayList<BackStackRecord> records,
ArrayList<Boolean> isRecordPop) {
......
// Force start of any postponed transactions that interact with scheduled transactions:
executePostponedTransaction(records, isRecordPop);
final int numRecords = records.size();
int startIndex = 0;
for (int recordNum = 0; recordNum < numRecords; recordNum++) {
final boolean canReorder = records.get(recordNum).mReorderingAllowed;
if (!canReorder) {
// execute all previous transactions
if (startIndex != recordNum) {
executeOpsTogether(records, isRecordPop, startIndex, recordNum);
}
// execute all pop operations that don't allow reordering together or
// one add operation
int reorderingEnd = recordNum + 1;
if (isRecordPop.get(recordNum)) {
while (reorderingEnd < numRecords
&& isRecordPop.get(reorderingEnd)
&& !records.get(reorderingEnd).mReorderingAllowed) {
reorderingEnd++;
}
}
// ⑤
executeOpsTogether(records, isRecordPop, recordNum, reorderingEnd);
startIndex = reorderingEnd;
recordNum = reorderingEnd - 1;
}
}
if (startIndex != numRecords) {
executeOpsTogether(records, isRecordPop, startIndex, numRecords);
}
}
private void executeOpsTogether(ArrayList<BackStackRecord> records,
ArrayList<Boolean> isRecordPop, int startIndex, int endIndex) {
......
if (!allowReordering) {
FragmentTransition.startTransitions(this, records, isRecordPop, startIndex, endIndex,
false);
}
executeOps(records, isRecordPop, startIndex, endIndex);
......
for (int recordNum = startIndex; recordNum < endIndex; recordNum++) {
final BackStackRecord record = records.get(recordNum);
final boolean isPop = isRecordPop.get(recordNum);
if (isPop && record.mIndex >= 0) {
freeBackStackIndex(record.mIndex);
record.mIndex = -1;
}
record.runOnCommitRunnables();
}
if (addToBackStack) {
reportBackStackChanged();
}
}
private static void executeOps(ArrayList<BackStackRecord> records,
ArrayList<Boolean> isRecordPop, int startIndex, int endIndex) {
for (int i = startIndex; i < endIndex; i++) {
final BackStackRecord record = records.get(i);
final boolean isPop = isRecordPop.get(i);
if (isPop) {
record.bumpBackStackNesting(-1);
// Only execute the add operations at the end of
// all transactions.
boolean moveToState = i == (endIndex - 1);
record.executePopOps(moveToState);
} else {
record.bumpBackStackNesting(1);
record.executeOps();
}
}
}
②：首先初始化mPendingActions，并将事件添加到mPendingActions列表中。然后执行 scheduleCommit()。
③：在scheduleCommit方法中，由于mPendingActions已经初始化过，且大小为1。pendingReady标记位为*true，*所以执行步骤④
④：通过Handler发送添加Fragment的执行事件，开始创建Fragment对象，执行各生命周期方法等。
⑤：执行executeOps方法，然后执行 record.executeOps()
// BackStackRecord.java
void executeOps() {
final int numOps = mOps.size();
for (int opNum = 0; opNum < numOps; opNum++) {
final Op op = mOps.get(opNum);
final Fragment f = op.mFragment;
if (f != null) {
f.setNextTransition(mTransition, mTransitionStyle);
}
switch (op.mCmd) {
case OP_ADD:
f.setNextAnim(op.mEnterAnim);
// ⑥
mManager.addFragment(f, false);
break;
case OP_REMOVE:
f.setNextAnim(op.mExitAnim);
mManager.removeFragment(f);
break;
case OP_HIDE:
f.setNextAnim(op.mExitAnim);
mManager.hideFragment(f);
break;
case OP_SHOW:
f.setNextAnim(op.mEnterAnim);
mManager.showFragment(f);
break;
case OP_DETACH:
f.setNextAnim(op.mExitAnim);
mManager.detachFragment(f);
break;
case OP_ATTACH:
f.setNextAnim(op.mEnterAnim);
mManager.attachFragment(f);
break;
case OP_SET_PRIMARY_NAV:
mManager.setPrimaryNavigationFragment(f);
break;
case OP_UNSET_PRIMARY_NAV:
mManager.setPrimaryNavigationFragment(null);
break;
case OP_SET_MAX_LIFECYCLE:
mManager.setMaxLifecycle(f, op.mCurrentMaxState);
break;
default:
throw new IllegalArgumentException("Unknown cmd: " + op.mCmd);
}
if (!mReorderingAllowed && op.mCmd != OP_ADD && f != null) {
mManager.moveFragmentToExpectedState(f);
}
}
if (!mReorderingAllowed) {
// ⑦
// Added fragments are added at the end to comply with prior behavior.
mManager.moveToState(mManager.mCurState, true);
}
}
⑥：还记得在调用add方法时，将OP_ADD指令保存了下来，所以这里在会调用 *mManager.addFragment(f, false)，*该方法主要做一些状态和标记位的设置。
// FragmentManagerImpl.java
public void addFragment(Fragment fragment, boolean moveToStateNow) {
if (DEBUG) Log.v(TAG, "add: " + fragment);
makeActive(fragment);
if (!fragment.mDetached) {
if (mAdded.contains(fragment)) {
throw new IllegalStateException("Fragment already added: " + fragment);
}
synchronized (mAdded) {
mAdded.add(fragment);
}
fragment.mAdded = true;
fragment.mRemoving = false;
if (fragment.mView == null) {
fragment.mHiddenChanged = false;
}
if (isMenuAvailable(fragment)) {
mNeedMenuInvalidate = true;
}
if (moveToStateNow) {
moveToState(fragment);
}
}
}
⑦：mManager.moveToState将fragment当前状态转化为下一个新状态
/**
* Changes the state of the fragment manager to {@code newState}. If the fragment manager
* changes state or {@code always} is {@code true}, any fragments within it have their
* states updated as well.
*
* @param newState The new state for the fragment manager
* @param always If {@code true}, all fragments update their state, even
* if {@code newState} matches the current fragment manager's state.
*/
void moveToState(int newState, boolean always) {
if (mHost == null && newState != Fragment.INITIALIZING) {
throw new IllegalStateException("No activity");
}
if (!always && newState == mCurState) {
return;
}
mCurState = newState;
// Must add them in the proper order. mActive fragments may be out of order
final int numAdded = mAdded.size();
for (int i = 0; i < numAdded; i++) {
Fragment f = mAdded.get(i);
moveFragmentToExpectedState(f);
}
// Now iterate through all active fragments. These will include those that are removed
// and detached.
for (Fragment f : mActive.values()) {
if (f != null && (f.mRemoving || f.mDetached) && !f.mIsNewlyAdded) {
moveFragmentToExpectedState(f);
}
}
startPendingDeferredFragments();
if (mNeedMenuInvalidate && mHost != null && mCurState == Fragment.RESUMED) {
mHost.onSupportInvalidateOptionsMenu();
mNeedMenuInvalidate = false;
}
}
void moveFragmentToExpectedState(Fragment f) {
if (f == null) {
return;
}
if (!mActive.containsKey(f.mWho)) {
if (DEBUG) {
Log.v(TAG, "Ignoring moving " + f + " to state " + mCurState
+ "since it is not added to " + this);
}
return;
}
int nextState = mCurState;
if (f.mRemoving) {
if (f.isInBackStack()) {
nextState = Math.min(nextState, Fragment.CREATED);
} else {
nextState = Math.min(nextState, Fragment.INITIALIZING);
}
}
// ⑧
moveToState(f, nextState, f.getNextTransition(), f.getNextTransitionStyle(), false);
......
}
⑧：这个方法就是Fragment添加到展示过程中，各生命周期方法和注册的FragmentLifecycleCallbacks监听的具体执行位置。该方法源码如下
@SuppressWarnings("ReferenceEquality")
void moveToState(Fragment f, int newState, int transit, int transitionStyle,
boolean keepActive) {
// Fragments that are not currently added will sit in the onCreate() state.
if ((!f.mAdded || f.mDetached) && newState > Fragment.CREATED) {
newState = Fragment.CREATED;
}
if (f.mRemoving && newState > f.mState) {
if (f.mState == Fragment.INITIALIZING && f.isInBackStack()) {
// Allow the fragment to be created so that it can be saved later.
newState = Fragment.CREATED;
} else {
// While removing a fragment, we can't change it to a higher state.
newState = f.mState;
}
}
// Defer start if requested; don't allow it to move to STARTED or higher
// if it's not already started.
if (f.mDeferStart && f.mState < Fragment.STARTED && newState > Fragment.ACTIVITY_CREATED) {
newState = Fragment.ACTIVITY_CREATED;
}
// Don't allow the Fragment to go above its max lifecycle state
// Ensure that Fragments are capped at CREATED instead of ACTIVITY_CREATED.
if (f.mMaxState == Lifecycle.State.CREATED) {
newState = Math.min(newState, Fragment.CREATED);
} else {
newState = Math.min(newState, f.mMaxState.ordinal());
}
if (f.mState <= newState) {
// For fragments that are created from a layout, when restoring from
// state we don't want to allow them to be created until they are
// being reloaded from the layout.
if (f.mFromLayout && !f.mInLayout) {
return;
}
if (f.getAnimatingAway() != null || f.getAnimator() != null) {
// The fragment is currently being animated... but! Now we
// want to move our state back up. Give up on waiting for the
// animation, move to whatever the final state should be once
// the animation is done, and then we can proceed from there.
f.setAnimatingAway(null);
f.setAnimator(null);
moveToState(f, f.getStateAfterAnimating(), 0, 0, true);
}
switch (f.mState) {
case Fragment.INITIALIZING:
if (newState > Fragment.INITIALIZING) {
if (DEBUG) Log.v(TAG, "moveto CREATED: " + f);
if (f.mSavedFragmentState != null) {
f.mSavedFragmentState.setClassLoader(mHost.getContext()
.getClassLoader());
f.mSavedViewState = f.mSavedFragmentState.getSparseParcelableArray(
FragmentManagerImpl.VIEW_STATE_TAG);
Fragment target = getFragment(f.mSavedFragmentState,
FragmentManagerImpl.TARGET_STATE_TAG);
f.mTargetWho = target != null ? target.mWho : null;
if (f.mTargetWho != null) {
f.mTargetRequestCode = f.mSavedFragmentState.getInt(
FragmentManagerImpl.TARGET_REQUEST_CODE_STATE_TAG, 0);
}
if (f.mSavedUserVisibleHint != null) {
f.mUserVisibleHint = f.mSavedUserVisibleHint;
f.mSavedUserVisibleHint = null;
} else {
f.mUserVisibleHint = f.mSavedFragmentState.getBoolean(
FragmentManagerImpl.USER_VISIBLE_HINT_TAG, true);
}
if (!f.mUserVisibleHint) {
f.mDeferStart = true;
if (newState > Fragment.ACTIVITY_CREATED) {
newState = Fragment.ACTIVITY_CREATED;
}
}
}
f.mHost = mHost;
f.mParentFragment = mParent;
f.mFragmentManager = mParent != null
? mParent.mChildFragmentManager : mHost.mFragmentManager;
// If we have a target fragment, push it along to at least CREATED
// so that this one can rely on it as an initialized dependency.
if (f.mTarget != null) {
if (mActive.get(f.mTarget.mWho) != f.mTarget) {
throw new IllegalStateException("Fragment " + f
+ " declared target fragment " + f.mTarget
+ " that does not belong to this FragmentManager!");
}
if (f.mTarget.mState < Fragment.CREATED) {
moveToState(f.mTarget, Fragment.CREATED, 0, 0, true);
}
f.mTargetWho = f.mTarget.mWho;
f.mTarget = null;
}
if (f.mTargetWho != null) {
Fragment target = mActive.get(f.mTargetWho);
if (target == null) {
throw new IllegalStateException("Fragment " + f
+ " declared target fragment " + f.mTargetWho
+ " that does not belong to this FragmentManager!");
}
if (target.mState < Fragment.CREATED) {
moveToState(target, Fragment.CREATED, 0, 0, true);
}
}
dispatchOnFragmentPreAttached(f, mHost.getContext(), false);
f.performAttach();
if (f.mParentFragment == null) {
mHost.onAttachFragment(f);
} else {
f.mParentFragment.onAttachFragment(f);
}
dispatchOnFragmentAttached(f, mHost.getContext(), false);
if (!f.mIsCreated) {
dispatchOnFragmentPreCreated(f, f.mSavedFragmentState, false);
f.performCreate(f.mSavedFragmentState);
dispatchOnFragmentCreated(f, f.mSavedFragmentState, false);
} else {
f.restoreChildFragmentState(f.mSavedFragmentState);
f.mState = Fragment.CREATED;
}
}
// fall through
case Fragment.CREATED:
// We want to unconditionally run this anytime we do a moveToState that
// moves the Fragment above INITIALIZING, including cases such as when
// we move from CREATED => CREATED as part of the case fall through above.
if (newState > Fragment.INITIALIZING) {
ensureInflatedFragmentView(f);
}
if (newState > Fragment.CREATED) {
if (DEBUG) Log.v(TAG, "moveto ACTIVITY_CREATED: " + f);
if (!f.mFromLayout) {
ViewGroup container = null;
if (f.mContainerId != 0) {
if (f.mContainerId == View.NO_ID) {
throwException(new IllegalArgumentException(
"Cannot create fragment "
+ f
+ " for a container view with no id"));
}
container = (ViewGroup) mContainer.onFindViewById(f.mContainerId);
if (container == null && !f.mRestored) {
String resName;
try {
resName = f.getResources().getResourceName(f.mContainerId);
} catch (Resources.NotFoundException e) {
resName = "unknown";
}
throwException(new IllegalArgumentException(
"No view found for id 0x"
+ Integer.toHexString(f.mContainerId) + " ("
+ resName
+ ") for fragment " + f));
}
}
f.mContainer = container;
f.performCreateView(f.performGetLayoutInflater(
f.mSavedFragmentState), container, f.mSavedFragmentState);
if (f.mView != null) {
f.mInnerView = f.mView;
f.mView.setSaveFromParentEnabled(false);
if (container != null) {
container.addView(f.mView);
}
if (f.mHidden) {
f.mView.setVisibility(View.GONE);
}
f.onViewCreated(f.mView, f.mSavedFragmentState);
dispatchOnFragmentViewCreated(f, f.mView, f.mSavedFragmentState,
false);
// Only animate the view if it is visible. This is done after
// dispatchOnFragmentViewCreated in case visibility is changed
f.mIsNewlyAdded = (f.mView.getVisibility() == View.VISIBLE)
&& f.mContainer != null;
} else {
f.mInnerView = null;
}
}
f.performActivityCreated(f.mSavedFragmentState);
dispatchOnFragmentActivityCreated(f, f.mSavedFragmentState, false);
if (f.mView != null) {
f.restoreViewState(f.mSavedFragmentState);
}
f.mSavedFragmentState = null;
}
// fall through
case Fragment.ACTIVITY_CREATED:
if (newState > Fragment.ACTIVITY_CREATED) {
if (DEBUG) Log.v(TAG, "moveto STARTED: " + f);
f.performStart();
dispatchOnFragmentStarted(f, false);
}
// fall through
case Fragment.STARTED:
if (newState > Fragment.STARTED) {
if (DEBUG) Log.v(TAG, "moveto RESUMED: " + f);
f.performResume();
dispatchOnFragmentResumed(f, false);
f.mSavedFragmentState = null;
f.mSavedViewState = null;
}
}
} else if (f.mState > newState) {
switch (f.mState) {
case Fragment.RESUMED:
if (newState < Fragment.RESUMED) {
if (DEBUG) Log.v(TAG, "movefrom RESUMED: " + f);
f.performPause();
dispatchOnFragmentPaused(f, false);
}
// fall through
case Fragment.STARTED:
if (newState < Fragment.STARTED) {
if (DEBUG) Log.v(TAG, "movefrom STARTED: " + f);
f.performStop();
dispatchOnFragmentStopped(f, false);
}
// fall through
case Fragment.ACTIVITY_CREATED:
if (newState < Fragment.ACTIVITY_CREATED) {
if (DEBUG) Log.v(TAG, "movefrom ACTIVITY_CREATED: " + f);
if (f.mView != null) {
// Need to save the current view state if not
// done already.
if (mHost.onShouldSaveFragmentState(f) && f.mSavedViewState == null) {
saveFragmentViewState(f);
}
}
f.performDestroyView();
dispatchOnFragmentViewDestroyed(f, false);
if (f.mView != null && f.mContainer != null) {
// Stop any current animations:
f.mContainer.endViewTransition(f.mView);
f.mView.clearAnimation();
AnimationOrAnimator anim = null;
// If parent is being removed, no need to handle child animations.
if (f.getParentFragment() == null || !f.getParentFragment().mRemoving) {
if (mCurState > Fragment.INITIALIZING && !mDestroyed
&& f.mView.getVisibility() == View.VISIBLE
&& f.mPostponedAlpha >= 0) {
anim = loadAnimation(f, transit, false,
transitionStyle);
}
f.mPostponedAlpha = 0;
if (anim != null) {
animateRemoveFragment(f, anim, newState);
}
f.mContainer.removeView(f.mView);
}
}
f.mContainer = null;
f.mView = null;
// Set here to ensure that Observers are called after
// the Fragment's view is set to null
f.mViewLifecycleOwner = null;
f.mViewLifecycleOwnerLiveData.setValue(null);
f.mInnerView = null;
f.mInLayout = false;
}
// fall through
case Fragment.CREATED:
if (newState < Fragment.CREATED) {
if (mDestroyed) {
// The fragment's containing activity is
// being destroyed, but this fragment is
// currently animating away. Stop the
// animation right now -- it is not needed,
// and we can't wait any more on destroying
// the fragment.
if (f.getAnimatingAway() != null) {
View v = f.getAnimatingAway();
f.setAnimatingAway(null);
v.clearAnimation();
} else if (f.getAnimator() != null) {
Animator animator = f.getAnimator();
f.setAnimator(null);
animator.cancel();
}
}
if (f.getAnimatingAway() != null || f.getAnimator() != null) {
// We are waiting for the fragment's view to finish
// animating away. Just make a note of the state
// the fragment now should move to once the animation
// is done.
f.setStateAfterAnimating(newState);
newState = Fragment.CREATED;
} else {
if (DEBUG) Log.v(TAG, "movefrom CREATED: " + f);
boolean beingRemoved = f.mRemoving && !f.isInBackStack();
if (beingRemoved || mNonConfig.shouldDestroy(f)) {
boolean shouldClear;
if (mHost instanceof ViewModelStoreOwner) {
shouldClear = mNonConfig.isCleared();
} else if (mHost.getContext() instanceof Activity) {
Activity activity = (Activity) mHost.getContext();
shouldClear = !activity.isChangingConfigurations();
} else {
shouldClear = true;
}
if (beingRemoved || shouldClear) {
mNonConfig.clearNonConfigState(f);
}
f.performDestroy();
dispatchOnFragmentDestroyed(f, false);
} else {
f.mState = Fragment.INITIALIZING;
}
f.performDetach();
dispatchOnFragmentDetached(f, false);
if (!keepActive) {
if (beingRemoved || mNonConfig.shouldDestroy(f)) {
makeInactive(f);
} else {
f.mHost = null;
f.mParentFragment = null;
f.mFragmentManager = null;
if (f.mTargetWho != null) {
Fragment target = mActive.get(f.mTargetWho);
if (target != null && target.getRetainInstance()) {
// Only keep references to other retained Fragments
// to avoid developers accessing Fragments that
// are never coming back
f.mTarget = target;
}
}
}
}
}
}
}
}
if (f.mState != newState) {
Log.w(TAG, "moveToState: Fragment state for " + f + " not updated inline; "
+ "expected state " + newState + " found " + f.mState);
f.mState = newState;
}
}
代码很长，但还是比较容易看出，在INITIALIZING状态下，先后执行了onFragmentPreAttach、onAttach、onFragmentAttched、onFragmentPreCreate、onCreate等
在CREATE状态下，执行了onCreateView、onViewCreated、onActivityCreated等方法。
二、DialogFragment
2.1 DialogFragment生命周期
查看DialogFragment的继承关系，其实它继承自Fragment，所以具备Fragment的特性和生命周期方法。同时，DialogFragment也具有一些Dialog的特点，反应在生命周期方法调用流程上就是，在onCreateView前，会调用onCreateDialog方法。
图 3 DialogFragment生命周期流程图
看下Fragment执行onCreateView的源码：
void moveToState(Fragment f, int newState, int transit, int transitionStyle,
boolean keepActive) {
......
switch (f.mState) {
case Fragment.INITIALIZING:
......
// fall through
case Fragment.CREATED:
......
if (newState > Fragment.CREATED) {
if (DEBUG) Log.v(TAG, "moveto ACTIVITY_CREATED: " + f);
......
f.mContainer = container;
// ⑩
f.performCreateView(f.performGetLayoutInflater(
f.mSavedFragmentState), container, f.mSavedFragmentState);
......
}
f.performActivityCreated(f.mSavedFragmentState);
dispatchOnFragmentActivityCreated(f, f.mSavedFragmentState, false);
if (f.mView != null) {
f.restoreViewState(f.mSavedFragmentState);
}
f.mSavedFragmentState = null;
}
// fall through
case Fragment.ACTIVITY_CREATED:
if (newState > Fragment.ACTIVITY_CREATED) {
if (DEBUG) Log.v(TAG, "moveto STARTED: " + f);
f.performStart();
dispatchOnFragmentStarted(f, false);
}
// fall through
case Fragment.STARTED:
if (newState > Fragment.STARTED) {
if (DEBUG) Log.v(TAG, "moveto RESUMED: " + f);
f.performResume();
dispatchOnFragmentResumed(f, false);
f.mSavedFragmentState = null;
f.mSavedViewState = null;
}
}
}
⑩：在performCreateView时，需要传入LayoutInflater对象作为参数。LayoutInflater对象通过performGetLayoutInflater方法获取，查看方法performGetLayoutInflater。
LayoutInflater performGetLayoutInflater(@Nullable Bundle savedInstanceState) {
LayoutInflater layoutInflater = onGetLayoutInflater(savedInstanceState);
mLayoutInflater = layoutInflater;
return mLayoutInflater;
}
实际是调用了onGetLayoutInflater方法，对于DialogFragment来说，它重写了该方法，并在其中调用了*onCreateDialog，*源码如下
@Override
@NonNull
public LayoutInflater onGetLayoutInflater(@Nullable Bundle savedInstanceState) {
if (!mShowsDialog) {
return super.onGetLayoutInflater(savedInstanceState);
}
mDialog = onCreateDialog(savedInstanceState);
if (mDialog != null) {
setupDialog(mDialog, mStyle);
return (LayoutInflater) mDialog.getContext().getSystemService(
Context.LAYOUT_INFLATER_SERVICE);
}
return (LayoutInflater) mHost.getContext().getSystemService(
Context.LAYOUT_INFLATER_SERVICE);
}
三、BottomSheetDialogFragment
BottomSheetDialogFragment继承自DialogFragment，也就是说它也具有DialogFragment的一些特性（或者更具体点说是Fragment的特性）。BottomSheetDialogFragment作为底部弹出式的视图，我们通常会将它和BottomSheetBehavior结合使用，来完成更复杂的交互或其他功能。
3.1 BottomSheetBehavior
BottomSheetBehavior使用还是比较简单，创建BottomSheetBehavior对象，和需要联动的View进行绑定即可。示例代码如下：
......
mBehavior = BottomSheetBehavior.from((View) view.getParent());
mBehavior.addBottomSheetCallback(bottomSheetCallback);
mBehavior.setPeekHeight(ScreenUtils.getScreenHeight(getContext()));
......
注意：BottomSheetBehavior.from方法要求传入的View的LayoutParams必须是CoordinatorLayout的LayoutParams。但这不意味着我们创建的View的根布局就必须是CoordinatorLayout，它会自动给我们包一层，这个下面会详述。
通过BottomSheetBehavior，我们可以添加一些滑动和Fling的监听事件，或者设置BottomSheetDialogFragment打开时的初始高度等。
问题：
1）调用BottomSheetBehavior.from方法时，传入的是view.getParent()，因为这个view的根布局不是*CoordinatorLayout，如果传入view，*会报异常
java.lang.IllegalArgumentException: The view is not a child of CoordinatorLayout
at com.google.android.material.bottomsheet.BottomSheetBehavior.from(BottomSheetBehavior.java:1634)
2）如果传入view.getParent()（也就是前面提到过的BottomSheetDialogFragment会给我们的view包一层CoordinatorLayout的布局），无论是在onCreateView或onViewCreated生命周期方法中去创建BottomSheetBehavior对象，会报错并提示
java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.ViewGroup$LayoutParams android.view.View.getLayoutParams()' on a null object reference
at com.google.android.material.bottomsheet.BottomSheetBehavior.from(BottomSheetBehavior.java:1632)
说明此时我们的*view.getParent()*还没创建好，所以出现空指针。那么就需要确定下view.*getParent()*创建的时机。
排查：
BottomSheetDialogFragment是DialogFragment的子类，那么会依次执行DialogFragment的生命周期方法，因此排查就是依次看下这些方法执行了什么逻辑。
-
根据图3，在onCreateDialog方法新建了BottomSheetDialog对象，并且创建了Dialog的window对象以及设置了WindowManager对象。
-
onCreateView仅创建了View对象，onViewCreated是空方法，这2个方法看起来比较正常。
-
onActivityCreated给Dialog设置了需要展示的View和一些监听事件，代码如下
// DialogFragment.java @Override public void onActivityCreated(@Nullable Bundle savedInstanceState) { super.onActivityCreated(savedInstanceState); if (!mShowsDialog) { return; } View view = getView(); if (view != null) { if (view.getParent() != null) { throw new IllegalStateException( "DialogFragment can not be attached to a container view"); } // ① mDialog.setContentView(view); } final Activity activity = getActivity(); if (activity != null) { mDialog.setOwnerActivity(activity); } mDialog.setCancelable(mCancelable); mDialog.setOnCancelListener(this); mDialog.setOnDismissListener(this); if (savedInstanceState != null) { Bundle dialogState = savedInstanceState.getBundle(SAVED_DIALOG_STATE_TAG); if (dialogState != null) { mDialog.onRestoreInstanceState(dialogState); } } }①：看下Dialog的setContentView方法，由于BottomSheetDialogFragment在onCreateDialog方法创建的是BottomSheetDialog对象，而BottomSheetDialog类有重写了setContentView方法，所以查看BottomSheetDialog#setContentView方法源码
// BottomSheetDialog.java @Override public void setContentView(@LayoutRes int layoutResId) { super.setContentView(wrapInBottomSheet(layoutResId, null, null)); } private View wrapInBottomSheet( int layoutResId, @Nullable View view, @Nullable ViewGroup.LayoutParams params) { ensureContainerAndBehavior(); CoordinatorLayout coordinator = (CoordinatorLayout) container.findViewById(R.id.coordinator); if (layoutResId != 0 && view == null) { view = getLayoutInflater().inflate(layoutResId, coordinator, false); } FrameLayout bottomSheet = (FrameLayout) container.findViewById(R.id.design_bottom_sheet); bottomSheet.removeAllViews(); // ② if (params == null) { bottomSheet.addView(view); } else { bottomSheet.addView(view, params); } // We treat the CoordinatorLayout as outside the dialog though it is technically inside coordinator .findViewById(R.id.touch_outside) .setOnClickListener( new View.OnClickListener() { @Override public void onClick(View view) { if (cancelable && isShowing() && shouldWindowCloseOnTouchOutside()) { cancel(); } } }); // Handle accessibility events ViewCompat.setAccessibilityDelegate( bottomSheet, new AccessibilityDelegateCompat() { @Override public void onInitializeAccessibilityNodeInfo( View host, @NonNull AccessibilityNodeInfoCompat info) { super.onInitializeAccessibilityNodeInfo(host, info); if (cancelable) { info.addAction(AccessibilityNodeInfoCompat.ACTION_DISMISS); info.setDismissable(true); } else { info.setDismissable(false); } } @Override public boolean performAccessibilityAction(View host, int action, Bundle args) { if (action == AccessibilityNodeInfoCompat.ACTION_DISMISS && cancelable) { cancel(); return true; } return super.performAccessibilityAction(host, action, args); } }); bottomSheet.setOnTouchListener( new View.OnTouchListener() { @Override public boolean onTouch(View view, MotionEvent event) { // Consume the event and prevent it from falling through return true; } }); return container; }②：重点就在wrapInBottomSheet方法，虽然我们构造自己的View时没有使用CoordinatorLayout，但在该方法中，系统有个默认的布局文件R.layout.design_bottom_sheet_dialog（见下方代码），wrapInBottomSheet方法就是将我们的布局添加到默认布局中(id为design_bottom_sheet的FrameLayout)，我们的布局的父视图就是CoordinatorLayout了，从而不必我们自己去设置CoordinatorLayout为根布局。
// R.layout.design_bottom_sheet_dialog <?xml version="1.0" encoding="utf-8"?> <!-- ~ Copyright (C) 2015 The Android Open Source Project ~ ~ Licensed under the Apache License, Version 2.0 (the "License"); ~ you may not use this file except in compliance with the License. ~ You may obtain a copy of the License at ~ ~ http://www.apache.org/licenses/LICENSE-2.0 ~ ~ Unless required by applicable law or agreed to in writing, software ~ distributed under the License is distributed on an "AS IS" BASIS, ~ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. ~ See the License for the specific language governing permissions and ~ limitations under the License. --> <FrameLayout 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:id="@+id/container" android:layout_width="match_parent" android:layout_height="match_parent" android:fitsSystemWindows="true"> <android.support.design.widget.CoordinatorLayout android:id="@+id/coordinator" android:layout_width="match_parent" android:layout_height="match_parent" android:fitsSystemWindows="true"> <View android:id="@+id/touch_outside" android:layout_width="match_parent" android:layout_height="match_parent" android:importantForAccessibility="no" android:soundEffectsEnabled="false" tools:ignore="UnusedAttribute"/> <FrameLayout android:id="@+id/design_bottom_sheet" style="?attr/bottomSheetStyle" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_gravity="center_horizontal|top" app:layout_behavior="@string/bottom_sheet_behavior"/> </android.support.design.widget.CoordinatorLayout> </FrameLayout>
总结
- 创建BottomSheetBehavior对象时，如果传入的View参数不是某个CoordinatorLayout的直接子View，则需要在onActivityCreated生命周期方法之后创建（如onActivityCreated、onStart等）。
- 如果传入的View参数不是某个CoordinatorLayout的直接子View，还需要在布局文件中给其设置layout_behavior属性，否则会报「he view is not associated with BottomSheetBehavior」异常。
