Context引发的血案：Android Dialog显示源码分析

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前言

随着移动端与前端技术的发展，越来越多的应用使用了混合开发的模式，最典型的代表就是小程序。这之中有肯定会涉及到前端与移动端的交互。

Android与前端常用的交互方式如下表：

JavaScript → AndroidAndroid → JavaScript
addJavascriptInterfaceloadUrl
shouldOverrideUrlLoadingevaluateJavascript
onJsPrompt/onJsConfirm/onJsAlert/

在Android和前端交互开发中，由于前端性能以及样式等相关原因，有一些控件的显示会通过前端传参Android原生显示。比如Dialog、DatePicker、Alert、Toast等。于是就引出了今天要讨论的问题。

前端：我发现有一个弹窗控件不显示，帮我查下原因。

Android：一般弹窗都是走的JS和Android的通信，我们会在addJavascriptInterface进行拦截，然后再显示，你不用查了，应该是我的问题我来看下吧。

Android：查了好久，怎么都没走到addJavascriptInterface，肯定是JS报错了，前端快接锅！

前端：为什么之前的版本没问题？

Android：（心虚......）不会真是我的问题吧，赶紧好好查查。

经过排查发现，这一个弹窗并不是走的前端和Android通信，而是使用了一个select标签，那么问题来了，为什么使用select突然不能正确显示了。

问题描述

本文源码分析基于Android API Level29

前端代码

select.html

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <title></title>
</head>
<body>
  <select>
    <option value="Java">Java</option>
    <option value="PHP">PHP</option>
    <option value="Go">Go</option>
    <option value="JavaScript">JavaScript</option>
  </select>
</body>
</html>

Android代码

MainActivity.java
  
public class MainActivity extends AppCompatActivity {

    private WebView webView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ViewGroup container = findViewById(R.id.container);
        webView = new WebView(getApplicationContext());
        webView.setLayoutParams(new LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, LinearLayout.LayoutParams.MATCH_PARENT));
        container.addView(webView);
        webView.loadUrl("file:android_asset/select.html");
    }
}
image-20210812145257603

以上是简化后的示例代码，当点击select标签的时候弹窗弹不出来并且控制台报错如下：

E/WindowManager: BadTokenException or InvalidDisplayException, clean up.

经查WebView传入不同的ApplicationContext导致弹窗无法正常显示，正常情况下传入Activity弹窗显示如下图：

image-20210803151607432

下图通过Layout Inspector可以看到 select 标签在Android层是AlertDialog显示，既然AlertDialog有问题，那么我们再把问题简化一下直接给AlertDialog传入Application Context应该也是有问题的，我们先来验证下。

验证的代码很简单如下：

findViewById(R.id.show_dialog).setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        new AlertDialog.Builder(getApplicationContext())
                .setTitle("Title")
                .setMessage("message")
                .create()
                .show();
    }
});

如果我们所愿，程序crash了。记住Unable to add window -- token null is not valid; is your activity running?这行日志，后面我们还会看到。

2021-08-03 15:36:00.112 19594-19594/com.sample.select E/WindowManager: BadTokenException or InvalidDisplayException, clean up.
2021-08-03 15:36:00.113 19594-19594/com.sample.select D/AndroidRuntime: Shutting down VM
    
    
    --------- beginning of crash
2021-08-03 15:36:00.113 19594-19594/com.sample.select E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.sample.select, PID: 19594
    android.view.WindowManager$BadTokenException: Unable to add window -- token null is not valid; is your activity running?
        at android.view.ViewRootImpl.setView(ViewRootImpl.java:1133)
        at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:409)
        at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:111)
        at android.app.Dialog.show(Dialog.java:342)
        at com.sample.select.MainActivity$1.onClick(MainActivity.java:34)
        at android.view.View.performClick(View.java:7567)
        at com.google.android.material.button.MaterialButton.performClick(MaterialButton.java:1119)
        at android.view.View.performClickInternal(View.java:7544)
        at android.view.View.access$3600(View.java:836)
        at android.view.View$PerformClick.run(View.java:28770)
        at android.os.Handler.handleCallback(Handler.java:938)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:233)
        at android.app.ActivityThread.main(ActivityThread.java:7892)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:656)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:967)

Dialog 显示源码分析

既然crash的日志和Dialog的显示相关，现在我们先不去看上面的报错，先顺着显示Dialog这条线看一下Dialog调用show方法的主要流程。

findViewById(R.id.show_dialog).setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
      // 点击按钮执行代码如下，这里先改成 ActivityContext
        new AlertDialog.Builder(MainActivity.this)
                .setTitle("Title")
                .setMessage("message")
                .create()
                .show();
    }
});

1.0 AlertDialog create

setTitle 和 setMessage 就是设置一些显示信息。重点看一下 create() 做的事情。

AlertDialog.java 
  
public AlertDialog create() {
    // Context has already been wrapped with the appropriate theme.
  	// 创建AlertDialog对象
    final AlertDialog dialog = new AlertDialog(P.mContext, 0, false);
    P.apply(dialog.mAlert);
    dialog.setCancelable(P.mCancelable);
    if (P.mCancelable) {
        dialog.setCanceledOnTouchOutside(true);
    }
    dialog.setOnCancelListener(P.mOnCancelListener);
    dialog.setOnDismissListener(P.mOnDismissListener);
    if (P.mOnKeyListener != null) {
        dialog.setOnKeyListener(P.mOnKeyListener);
    }
    return dialog;
}

1.1 调用 AlertDialog 构造方法

final AlertDialog dialog = new AlertDialog(P.mContext, 0, false) 最终会调到Dialog中。

Dialog.java
  
Dialog(@NonNull Context context, @StyleRes int themeResId, boolean createContextThemeWrapper) {
    if (createContextThemeWrapper) {
        if (themeResId == Resources.ID_NULL) {
            final TypedValue outValue = new TypedValue();
            context.getTheme().resolveAttribute(R.attr.dialogTheme, outValue, true);
            themeResId = outValue.resourceId;
        }
        mContext = new ContextThemeWrapper(context, themeResId);
    } else {
        mContext = context;
    }

  	// 通过context获取WindowManager
    mWindowManager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);

    // 创建PhoneWindow
    final Window w = new PhoneWindow(mContext);
    mWindow = w;
    w.setCallback(this);
    w.setOnWindowDismissedCallback(this);
    w.setOnWindowSwipeDismissedCallback(() -> {
        if (mCancelable) {
            cancel();
        }
    });
    
  	// 设置Window的WindowManager
    w.setWindowManager(mWindowManager, null, null);
    w.setGravity(Gravity.CENTER);

    mListenersHandler = new ListenersHandler(this);
}

我们可以看到在 Dialog 的构造方法中主要做了三件事

  • 通过context获取WindowManager（注意：这里的WindowManager和context有关，后面会重点看这里）
  • 创建PhoneWindow并赋值给mWindow。Window是一个抽象类，PhoneWindow是它的唯一实现类
  • 设置上一步Window的WindowManager

1.2 显示show

create完成之后走到了Dialog的show方法

Dialog.java
  
public void show() {
   // ...
    if (!mCreated) {
        dispatchOnCreate(null);
    } else {
        // Fill the DecorView in on any configuration changes that
        // may have occured while it was removed from the WindowManager.
        final Configuration config = mContext.getResources().getConfiguration();
        mWindow.getDecorView().dispatchConfigurationChanged(config);
    }
  
    onStart();
    mDecor = mWindow.getDecorView();

   // ...
  
    WindowManager.LayoutParams l = mWindow.getAttributes();
    boolean restoreSoftInputMode = false;
    if ((l.softInputMode
            & WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION) == 0) {
        l.softInputMode |=
                WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION;
        restoreSoftInputMode = true;
    }

    // 注意这个mWindowManager，是在这里报的错
    mWindowManager.addView(mDecor, l);
    if (restoreSoftInputMode) {
        l.softInputMode &=
                ~WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION;
    }

    mShowing = true;

    sendShowMessage();
}

这一步我们关心的重点如下：

  • 通过mWindow获取DecorView
  • 通过mWindowManager添加View：mWindowManager.addView(mDecor, l)

那么mDecor是通过mWindow获取的，它又是怎么设置的呢？我们再起一条子线看一下。

1.2.1 dispatchOnCreate

在show方法中先调用了dispatchOnCreate，代码如下：

Dialog.java
  
	void dispatchOnCreate(Bundle savedInstanceState) {
        if (!mCreated) {
            onCreate(savedInstanceState);
            mCreated = true;
        }
    }

1.2.2 onCreate

AlertDialog.java
  
		@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mAlert.installContent();
    }

1.2.3 installContent

AlertController.java

		@UnsupportedAppUsage
    public void installContent() {
        int contentView = selectContentView();//默认的布局文件
        mWindow.setContentView(contentView);
        setupView();
    }

1.2.4 setContentView

PhoneWindow.java
  
		@Override
    public void setContentView(int layoutResID) {
        // Note: FEATURE_CONTENT_TRANSITIONS may be set in the process of installing the window
        // decor, when theme attributes and the like are crystalized. Do not check the feature
        // before this happens.
        if (mContentParent == null) {
          	// 重点
            installDecor();
        } else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
            mContentParent.removeAllViews();
        }

        if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
            final Scene newScene = Scene.getSceneForLayout(mContentParent, layoutResID,
                    getContext());
            transitionTo(newScene);
        } else {
            mLayoutInflater.inflate(layoutResID, mContentParent);
        }
        mContentParent.requestApplyInsets();
        final Callback cb = getCallback();
        if (cb != null && !isDestroyed()) {
            cb.onContentChanged();
        }
        mContentParentExplicitlySet = true;
    }

1.2.5 installDecor

PhoneWindow.java
  
		private void installDecor() {
        mForceDecorInstall = false;
        if (mDecor == null) {
          	// 给mDecor赋值
            mDecor = generateDecor(-1);
            mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
            mDecor.setIsRootNamespace(true);
            if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) {
                mDecor.postOnAnimation(mInvalidatePanelMenuRunnable);
            }
        } else {
            mDecor.setWindow(this);
        }
      
        // ...
    }

1.2.6 generateDecor

 PhoneWindow.java
   
		protected DecorView generateDecor(int featureId) {
        // System process doesn't have application context and in that case we need to directly use
        // the context we have. Otherwise we want the application context, so we don't cling to the
        // activity.
        Context context;
        if (mUseDecorContext) {
            Context applicationContext = getContext().getApplicationContext();
            if (applicationContext == null) {
                context = getContext();
            } else {
                context = new DecorContext(applicationContext, getContext());
                if (mTheme != -1) {
                    context.setTheme(mTheme);
                }
            }
        } else {
            context = getContext();
        }
        return new DecorView(context, featureId, this, getAttributes());
    }

到这一步Window的DecorView就被赋值了。子线任务完成，我们再回到主线。

1.3 WindowManagerImpl addView

可以看到 show() 中调用了mWindowManager.addView(mDecor, l)，由WindowManager来完成把 View 作为窗口添加到 WMS。

在mWindowManager的获取过程中我们可以看到mWindowManager 的实现类是 WindowManagerImpl，接下来去 WindowManagerImpl中看下addView方法的实现。

WindowManagerImpl.java
  
private final WindowManagerGlobal mGlobal = WindowManagerGlobal.getInstance();  
  
@Override
public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
    applyDefaultToken(params);
    mGlobal.addView(view, params, mContext.getDisplay(), mParentWindow);
}

1.4 WindowManagerGlobal addView

WindowManagerImpl中调用的又是mGlobal.addView。而mGlobal.addView 是一个单例，在当前进程中只有一个实例对象。

WindowManagerGlobal.java

// 获取WindowManagerGlobal单例对象
@UnsupportedAppUsage
public static WindowManagerGlobal getInstance() {
    synchronized (WindowManagerGlobal.class) {
        if (sDefaultWindowManager == null) {
            sDefaultWindowManager = new WindowManagerGlobal();
        }
        return sDefaultWindowManager;
    }
}

//...
public void addView(View view, ViewGroup.LayoutParams params,
        Display display, Window parentWindow) {
    if (view == null) {
        throw new IllegalArgumentException("view must not be null");
    }
    if (display == null) {
        throw new IllegalArgumentException("display must not be null");
    }
    if (!(params instanceof WindowManager.LayoutParams)) {
        throw new IllegalArgumentException("Params must be WindowManager.LayoutParams");
    }

    final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams) params;
    if (parentWindow != null) {
        parentWindow.adjustLayoutParamsForSubWindow(wparams);
    } else {
        // If there's no parent, then hardware acceleration for this view is
        // set from the application's hardware acceleration setting.
        final Context context = view.getContext();
        if (context != null
                && (context.getApplicationInfo().flags
                        & ApplicationInfo.FLAG_HARDWARE_ACCELERATED) != 0) {
            wparams.flags |= WindowManager.LayoutParams.FLAG_HARDWARE_ACCELERATED;
        }
    }

    ViewRootImpl root;
    View panelParentView = null;

    synchronized (mLock) {
        // Start watching for system property changes.
        if (mSystemPropertyUpdater == null) {
            mSystemPropertyUpdater = new Runnable() {
                @Override public void run() {
                    synchronized (mLock) {
                        for (int i = mRoots.size() - 1; i >= 0; --i) {
                            mRoots.get(i).loadSystemProperties();
                        }
                    }
                }
            };
            SystemProperties.addChangeCallback(mSystemPropertyUpdater);
        }

        int index = findViewLocked(view, false);
        if (index >= 0) {
            if (mDyingViews.contains(view)) {
                // Don't wait for MSG_DIE to make it's way through root's queue.
                mRoots.get(index).doDie();
            } else {
                throw new IllegalStateException("View " + view
                        + " has already been added to the window manager.");
            }
            // The previous removeView() had not completed executing. Now it has.
        }

        // If this is a panel window, then find the window it is being
        // attached to for future reference.
        if (wparams.type >= WindowManager.LayoutParams.FIRST_SUB_WINDOW &&
                wparams.type <= WindowManager.LayoutParams.LAST_SUB_WINDOW) {
            final int count = mViews.size();
            for (int i = 0; i < count; i++) {
                if (mRoots.get(i).mWindow.asBinder() == wparams.token) {
                    panelParentView = mViews.get(i);
                }
            }
        }

      	//创建ViewRootImpl
        root = new ViewRootImpl(view.getContext(), display);

        view.setLayoutParams(wparams);

        mViews.add(view);
        mRoots.add(root);
        mParams.add(wparams);

        // do this last because it fires off messages to start doing things
        try {
            root.setView(view, wparams, panelParentView);
        } catch (RuntimeException e) {
            // BadTokenException or InvalidDisplayException, clean up.
            if (index >= 0) {
                removeViewLocked(index, true);
            }
            throw e;
        }
    }
}

在 WindowManagerGlobal的addView方法中创建了ViewRootImpl，我们看下 root.setView(view, wparams, panelParentView) 做了哪些事情。

1.5 ViewRootImpl setView

ViewRootImpl.java

public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {
    synchronized (this) {
        if (mView == null) {
           
         		//...
            int res; /* = WindowManagerImpl.ADD_OKAY; */

            requestLayout();
            if ((mWindowAttributes.inputFeatures
                    & WindowManager.LayoutParams.INPUT_FEATURE_NO_INPUT_CHANNEL) == 0) {
                mInputChannel = new InputChannel();
            }
            mForceDecorViewVisibility = (mWindowAttributes.privateFlags
                    & PRIVATE_FLAG_FORCE_DECOR_VIEW_VISIBILITY) != 0;
            try {
                mOrigWindowType = mWindowAttributes.type;
                mAttachInfo.mRecomputeGlobalAttributes = true;
                collectViewAttributes();
              	// 这里给res进行了赋值
                res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
                        getHostVisibility(), mDisplay.getDisplayId(), mTmpFrame,
                        mAttachInfo.mContentInsets, mAttachInfo.mStableInsets,
                        mAttachInfo.mOutsets, mAttachInfo.mDisplayCutout, mInputChannel,
                        mTempInsets);
                setFrame(mTmpFrame);
            } catch (RemoteException e) {
                mAdded = false;
                mView = null;
                mAttachInfo.mRootView = null;
                mInputChannel = null;
                mFallbackEventHandler.setView(null);
                unscheduleTraversals();
                setAccessibilityFocus(null, null);
                throw new RuntimeException("Adding window failed", e);
            } finally {
                if (restore) {
                    attrs.restore();
                }
            }
						//...
            if (DEBUG_LAYOUT) Log.v(mTag, "Added window " + mWindow);
            if (res < WindowManagerGlobal.ADD_OKAY) {
                mAttachInfo.mRootView = null;
                mAdded = false;
                mFallbackEventHandler.setView(null);
                unscheduleTraversals();
                setAccessibilityFocus(null, null);
                switch (res) {
                    case WindowManagerGlobal.ADD_BAD_APP_TOKEN:
                    case WindowManagerGlobal.ADD_BAD_SUBWINDOW_TOKEN:
                    		// 对res进行判断，终于看到了上面我们熟悉的日志，crash的原因正是代码走进了这个分支
                        throw new WindowManager.BadTokenException(
                                "Unable to add window -- token " + attrs.token
                                + " is not valid; is your activity running?");
                    case WindowManagerGlobal.ADD_NOT_APP_TOKEN:
                        throw new WindowManager.BadTokenException(
                                "Unable to add window -- token " + attrs.token
                                + " is not for an application");
                    case WindowManagerGlobal.ADD_APP_EXITING:
                        throw new WindowManager.BadTokenException(
                                "Unable to add window -- app for token " + attrs.token
                                + " is exiting");
                    case WindowManagerGlobal.ADD_DUPLICATE_ADD:
                        throw new WindowManager.BadTokenException(
                                "Unable to add window -- window " + mWindow
                                + " has already been added");
                    case WindowManagerGlobal.ADD_STARTING_NOT_NEEDED:
                        // Silently ignore -- we would have just removed it
                        // right away, anyway.
                        return;
                    case WindowManagerGlobal.ADD_MULTIPLE_SINGLETON:
                        throw new WindowManager.BadTokenException("Unable to add window "
                                + mWindow + " -- another window of type "
                                + mWindowAttributes.type + " already exists");
                    case WindowManagerGlobal.ADD_PERMISSION_DENIED:
                        throw new WindowManager.BadTokenException("Unable to add window "
                                + mWindow + " -- permission denied for window type "
                                + mWindowAttributes.type);
                    case WindowManagerGlobal.ADD_INVALID_DISPLAY:
                        throw new WindowManager.InvalidDisplayException("Unable to add window "
                                + mWindow + " -- the specified display can not be found");
                    case WindowManagerGlobal.ADD_INVALID_TYPE:
                        throw new WindowManager.InvalidDisplayException("Unable to add window "
                                + mWindow + " -- the specified window type "
                                + mWindowAttributes.type + " is not valid");
                }
                throw new RuntimeException(
                        "Unable to add window -- unknown error code " + res);
            }

           //...
        }
    }
}

到这，如果res < WindowManagerGlobal.ADD_OKAY 就可以看到我们上面的报错了

Unable to add window -- token null is not valid; is your activity running?

这里如果我们传的是Activity的话返回值是大于0（ADD_OKAY）的。传入Application res的值是-1。

错误分析

有了上面的基础，接着上面我们分析res是怎么来的，res是mWindowSession.addToDisplay的返回值，那mWindowSession是什么?

通过下图和下面的代码可以看到很明显mWindowSession是一个Binder。

ViewRootImpl.java

@UnsupportedAppUsage
final IWindowSession mWindowSession;  

//...
  
res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
        getHostVisibility(), mDisplay.getDisplayId(), mTmpFrame,
        mAttachInfo.mContentInsets, mAttachInfo.mStableInsets,
        mAttachInfo.mOutsets, mAttachInfo.mDisplayCutout, mInputChannel,
        mTempInsets)

IWindowSession.aidl

interface IWindowSession {
    int addToDisplay(IWindow window, int seq, in WindowManager.LayoutParams attrs,
            in int viewVisibility, in int layerStackId, out Rect outFrame,
            out Rect outContentInsets, out Rect outStableInsets,
            out DisplayCutout.ParcelableWrapper displayCutout, out InputChannel outInputChannel,
            out InsetsState insetsState, out InsetsSourceControl[] activeControls);
    int addToDisplayAsUser(IWindow window, int seq, in WindowManager.LayoutParams attrs,
                in int viewVisibility, in int layerStackId, in int userId,
                out Rect outFrame, out Rect outContentInsets, out Rect outStableInsets,
                out DisplayCutout.ParcelableWrapper displayCutout, out InputChannel outInputChannel,
                out InsetsState insetsState, out InsetsSourceControl[] activeControls);
    int addToDisplayWithoutInputChannel(IWindow window, int seq, in WindowManager.LayoutParams attrs,
            in int viewVisibility, in int layerStackId, out Rect outContentInsets,
            out Rect outStableInsets, out InsetsState insetsState);
    @UnsupportedAppUsage
    void remove(IWindow window);
    int relayout(IWindow window, int seq, in WindowManager.LayoutParams attrs,
            int requestedWidth, int requestedHeight, int viewVisibility,
            int flags, long frameNumber, out Rect outFrame,
            out Rect outContentInsets, out Rect outVisibleInsets, out Rect outStableInsets,
            out Rect outBackdropFrame,
            out DisplayCutout.ParcelableWrapper displayCutout,
            out MergedConfiguration outMergedConfiguration, out SurfaceControl outSurfaceControl,
            out InsetsState insetsState, out InsetsSourceControl[] activeControls,
            out Point outSurfaceSize, out SurfaceControl outBlastSurfaceControl);
}

mWindowSession是一个运行在应用进程的Binder，它是在ViewRootImpl创建时初始化的。

ViewRootImpl.java

public ViewRootImpl(Context context, Display display) {
    mContext = context;
    mWindowSession = WindowManagerGlobal.getWindowSession();
    mDisplay = display;
    //...
}

在ViewRootImpl的构造方法中调用了WindowManagerGlobal.getWindowSession()

WindowManagerGlobal.java

public static IWindowSession getWindowSession() {
    synchronized (WindowManagerGlobal.class) {
        if (sWindowSession == null) {
            try {
                // Emulate the legacy behavior.  The global instance of InputMethodManager
                // was instantiated here.
                // TODO(b/116157766): Remove this hack after cleaning up @UnsupportedAppUsage
                InputMethodManager.ensureDefaultInstanceForDefaultDisplayIfNecessary();
                IWindowManager windowManager = getWindowManagerService();
                s  WindowSession = windowManager.openSession(
                        new IWindowSessionCallback.Stub() {
                            @Override
                            public void onAnimatorScaleChanged(float scale) {
                                ValueAnimator.setDurationScale(scale);
                            }
                        });
            } catch (RemoteException e) {
                throw e.rethrowFromSystemServer();
            }
        }
        return sWindowSession;
    }
}

在system_server进程IWindowSession对应的是Session。

Session.java

class Session extends IWindowSession.Stub implements IBinder.DeathRecipient {
    final WindowManagerService mService;
    final IWindowSessionCallback mCallback;
    final int mUid;
    final int mPid;
    private final String mStringName;
    SurfaceSession mSurfaceSession;
    private int mNumWindow = 0;
    // Set of visible application overlay window surfaces connected to this session.
    private final Set<WindowSurfaceController> mAppOverlaySurfaces = new HashSet<>();
    // Set of visible alert window surfaces connected to this session.
    private final Set<WindowSurfaceController> mAlertWindowSurfaces = new HashSet<>();
    private final DragDropController mDragDropController;
    final boolean mCanAddInternalSystemWindow;
    final boolean mCanHideNonSystemOverlayWindows;
    final boolean mCanAcquireSleepToken;
    private AlertWindowNotification mAlertWindowNotification;
    private boolean mShowingAlertWindowNotificationAllowed;
    private boolean mClientDead = false;
    private float mLastReportedAnimatorScale;
    private String mPackageName;
    private String mRelayoutTag;

    @Override
    public boolean onTransact(int code, Parcel data, Parcel reply, int flags)
            throws RemoteException {
        try {
            return super.onTransact(code, data, reply, flags);
        } catch (RuntimeException e) {
            if (!(e instanceof SecurityException)) {
                Slog.wtf(TAG_WM, "Window Session Crash", e);
            }
            throw e;
        }
    }

    @Override
    public int addToDisplay(IWindow window, int seq, WindowManager.LayoutParams attrs,
            int viewVisibility, int displayId, Rect outFrame, Rect outContentInsets,
            Rect outStableInsets, Rect outOutsets,
            DisplayCutout.ParcelableWrapper outDisplayCutout, InputChannel outInputChannel,
            InsetsState outInsetsState) {
        return mService.addWindow(this, window, seq, attrs, viewVisibility, displayId, outFrame,
                outContentInsets, outStableInsets, outOutsets, outDisplayCutout, outInputChannel,
                outInsetsState);
    }
	//...
}

Session的addToDisplay又调用了mService.addWindow()，这里的mService也就是我们熟悉的 WindowManagerService 了。

WindowManagerService.java

public int addWindow(Session session, IWindow client, int seq,
        LayoutParams attrs, int viewVisibility, int displayId, Rect outFrame,
        Rect outContentInsets, Rect outStableInsets, Rect outOutsets,
        DisplayCutout.ParcelableWrapper outDisplayCutout, InputChannel outInputChannel,
        InsetsState outInsetsState) {
    int[] appOp = new int[1];
    int res = mPolicy.checkAddPermission(attrs, appOp);
    if (res != WindowManagerGlobal.ADD_OKAY) {
        return res;
    }

    boolean reportNewConfig = false;
    WindowState parentWindow = null;
    long origId;
    final int callingUid = Binder.getCallingUid();
  	// 在这里给type赋值
    final int type = attrs.type;

    synchronized (mGlobalLock) {
        if (!mDisplayReady) {
            throw new IllegalStateException("Display has not been initialialized");
        }

        final DisplayContent displayContent = getDisplayContentOrCreate(displayId, attrs.token);

        if (displayContent == null) {
            Slog.w(TAG_WM, "Attempted to add window to a display that does not exist: "
                    + displayId + ".  Aborting.");
            return WindowManagerGlobal.ADD_INVALID_DISPLAY;
        }
        if (!displayContent.hasAccess(session.mUid)) {
            Slog.w(TAG_WM, "Attempted to add window to a display for which the application "
                    + "does not have access: " + displayId + ".  Aborting.");
            return WindowManagerGlobal.ADD_INVALID_DISPLAY;
        }

        if (mWindowMap.containsKey(client.asBinder())) {
            Slog.w(TAG_WM, "Window " + client + " is already added");
            return WindowManagerGlobal.ADD_DUPLICATE_ADD;
        }

        if (type >= FIRST_SUB_WINDOW && type <= LAST_SUB_WINDOW) {
          	// 在这里给parentWindow赋值
            parentWindow = windowForClientLocked(null, attrs.token, false);
            if (parentWindow == null) {
                Slog.w(TAG_WM, "Attempted to add window with token that is not a window: "
                      + attrs.token + ".  Aborting.");
                return WindowManagerGlobal.ADD_BAD_SUBWINDOW_TOKEN;
            }
            if (parentWindow.mAttrs.type >= FIRST_SUB_WINDOW
                    && parentWindow.mAttrs.type <= LAST_SUB_WINDOW) {
                Slog.w(TAG_WM, "Attempted to add window with token that is a sub-window: "
                        + attrs.token + ".  Aborting.");
                return WindowManagerGlobal.ADD_BAD_SUBWINDOW_TOKEN;
            }
        }

        if (type == TYPE_PRIVATE_PRESENTATION && !displayContent.isPrivate()) {
            Slog.w(TAG_WM, "Attempted to add private presentation window to a non-private display.  Aborting.");
            return WindowManagerGlobal.ADD_PERMISSION_DENIED;
        }

        AppWindowToken atoken = null;
        final boolean hasParent = parentWindow != null;
        // Use existing parent window token for child windows since they go in the same token
        // as there parent window so we can apply the same policy on them.
        WindowToken token = displayContent.getWindowToken(
                hasParent ? parentWindow.mAttrs.token : attrs.token);
        // If this is a child window, we want to apply the same type checking rules as the
        // parent window type.
        final int rootType = hasParent ? parentWindow.mAttrs.type : type;

        boolean addToastWindowRequiresToken = false;

      	// 重点看这里，token == null 会返回WindowManagerGlobal.ADD_BAD_APP_TOKEN
        if (token == null) {
            if (rootType >= FIRST_APPLICATION_WINDOW && rootType <= LAST_APPLICATION_WINDOW) {
                Slog.w(TAG_WM, "Attempted to add application window with unknown token "
                      + attrs.token + ".  Aborting.");
                return WindowManagerGlobal.ADD_BAD_APP_TOKEN;
            }
            if (rootType == TYPE_INPUT_METHOD) {
                Slog.w(TAG_WM, "Attempted to add input method window with unknown token "
                      + attrs.token + ".  Aborting.");
                return WindowManagerGlobal.ADD_BAD_APP_TOKEN;
            }
            if (rootType == TYPE_VOICE_INTERACTION) {
                Slog.w(TAG_WM, "Attempted to add voice interaction window with unknown token "
                      + attrs.token + ".  Aborting.");
                return WindowManagerGlobal.ADD_BAD_APP_TOKEN;
            }
            if (rootType == TYPE_WALLPAPER) {
                Slog.w(TAG_WM, "Attempted to add wallpaper window with unknown token "
                      + attrs.token + ".  Aborting.");
                return WindowManagerGlobal.ADD_BAD_APP_TOKEN;
            }
            if (rootType == TYPE_DREAM) {
                Slog.w(TAG_WM, "Attempted to add Dream window with unknown token "
                      + attrs.token + ".  Aborting.");
                return WindowManagerGlobal.ADD_BAD_APP_TOKEN;
            }
            if (rootType == TYPE_QS_DIALOG) {
                Slog.w(TAG_WM, "Attempted to add QS dialog window with unknown token "
                      + attrs.token + ".  Aborting.");
                return WindowManagerGlobal.ADD_BAD_APP_TOKEN;
            }
            if (rootType == TYPE_ACCESSIBILITY_OVERLAY) {
                Slog.w(TAG_WM, "Attempted to add Accessibility overlay window with unknown token "
                        + attrs.token + ".  Aborting.");
                return WindowManagerGlobal.ADD_BAD_APP_TOKEN;
            }
            if (type == TYPE_TOAST) {
                // Apps targeting SDK above N MR1 cannot arbitrary add toast windows.
                if (doesAddToastWindowRequireToken(attrs.packageName, callingUid,
                        parentWindow)) {
                    Slog.w(TAG_WM, "Attempted to add a toast window with unknown token "
                            + attrs.token + ".  Aborting.");
                    return WindowManagerGlobal.ADD_BAD_APP_TOKEN;
                }
            }
            final IBinder binder = attrs.token != null ? attrs.token : client.asBinder();
            final boolean isRoundedCornerOverlay =
                    (attrs.privateFlags & PRIVATE_FLAG_IS_ROUNDED_CORNERS_OVERLAY) != 0;
            token = new WindowToken(this, binder, type, false, displayContent,
                    session.mCanAddInternalSystemWindow, isRoundedCornerOverlay);
        } else if (rootType >= FIRST_APPLICATION_WINDOW && rootType <= LAST_APPLICATION_WINDOW) {
            atoken = token.asAppWindowToken();
            if (atoken == null) {
                Slog.w(TAG_WM, "Attempted to add window with non-application token "
                      + token + ".  Aborting.");
                return WindowManagerGlobal.ADD_NOT_APP_TOKEN;
            } else if (atoken.removed) {
                Slog.w(TAG_WM, "Attempted to add window with exiting application token "
                      + token + ".  Aborting.");
                return WindowManagerGlobal.ADD_APP_EXITING;
            } else if (type == TYPE_APPLICATION_STARTING && atoken.startingWindow != null) {
                Slog.w(TAG_WM, "Attempted to add starting window to token with already existing"
                        + " starting window");
                return WindowManagerGlobal.ADD_DUPLICATE_ADD;
            }
        } else if (rootType == TYPE_INPUT_METHOD) {
            if (token.windowType != TYPE_INPUT_METHOD) {
                Slog.w(TAG_WM, "Attempted to add input method window with bad token "
                        + attrs.token + ".  Aborting.");
                  return WindowManagerGlobal.ADD_BAD_APP_TOKEN;
            }
        } else if (rootType == TYPE_VOICE_INTERACTION) {
            if (token.windowType != TYPE_VOICE_INTERACTION) {
                Slog.w(TAG_WM, "Attempted to add voice interaction window with bad token "
                        + attrs.token + ".  Aborting.");
                  return WindowManagerGlobal.ADD_BAD_APP_TOKEN;
            }
        } else if (rootType == TYPE_WALLPAPER) {
            if (token.windowType != TYPE_WALLPAPER) {
                Slog.w(TAG_WM, "Attempted to add wallpaper window with bad token "
                        + attrs.token + ".  Aborting.");
                  return WindowManagerGlobal.ADD_BAD_APP_TOKEN;
            }
        } else if (rootType == TYPE_DREAM) {
            if (token.windowType != TYPE_DREAM) {
                Slog.w(TAG_WM, "Attempted to add Dream window with bad token "
                        + attrs.token + ".  Aborting.");
                  return WindowManagerGlobal.ADD_BAD_APP_TOKEN;
            }
        } else if (rootType == TYPE_ACCESSIBILITY_OVERLAY) {
            if (token.windowType != TYPE_ACCESSIBILITY_OVERLAY) {
                Slog.w(TAG_WM, "Attempted to add Accessibility overlay window with bad token "
                        + attrs.token + ".  Aborting.");
                return WindowManagerGlobal.ADD_BAD_APP_TOKEN;
            }
        } else if (type == TYPE_TOAST) {
            // Apps targeting SDK above N MR1 cannot arbitrary add toast windows.
            addToastWindowRequiresToken = doesAddToastWindowRequireToken(attrs.packageName,
                    callingUid, parentWindow);
            if (addToastWindowRequiresToken && token.windowType != TYPE_TOAST) {
                Slog.w(TAG_WM, "Attempted to add a toast window with bad token "
                        + attrs.token + ".  Aborting.");
                return WindowManagerGlobal.ADD_BAD_APP_TOKEN;
            }
        } else if (type == TYPE_QS_DIALOG) {
            if (token.windowType != TYPE_QS_DIALOG) {
                Slog.w(TAG_WM, "Attempted to add QS dialog window with bad token "
                        + attrs.token + ".  Aborting.");
                return WindowManagerGlobal.ADD_BAD_APP_TOKEN;
            }
        } else if (token.asAppWindowToken() != null) {
            Slog.w(TAG_WM, "Non-null appWindowToken for system window of rootType=" + rootType);
            // It is not valid to use an app token with other system types; we will
            // instead make a new token for it (as if null had been passed in for the token).
            attrs.token = null;
            token = new WindowToken(this, client.asBinder(), type, false, displayContent,
                    session.mCanAddInternalSystemWindow);
        }

        final WindowState win = new WindowState(this, session, client, token, parentWindow,
                appOp[0], seq, attrs, viewVisibility, session.mUid,
                session.mCanAddInternalSystemWindow);
        if (win.mDeathRecipient == null) {
            // Client has apparently died, so there is no reason to
            // continue.
            Slog.w(TAG_WM, "Adding window client " + client.asBinder()
                    + " that is dead, aborting.");
            return WindowManagerGlobal.ADD_APP_EXITING;
        }

        if (win.getDisplayContent() == null) {
            Slog.w(TAG_WM, "Adding window to Display that has been removed.");
            return WindowManagerGlobal.ADD_INVALID_DISPLAY;
        }

        final DisplayPolicy displayPolicy = displayContent.getDisplayPolicy();
        displayPolicy.adjustWindowParamsLw(win, win.mAttrs, Binder.getCallingPid(),
                Binder.getCallingUid());
        win.setShowToOwnerOnlyLocked(mPolicy.checkShowToOwnerOnly(attrs));

        res = displayPolicy.prepareAddWindowLw(win, attrs);
        if (res != WindowManagerGlobal.ADD_OKAY) {
            return res;
        }

        final boolean openInputChannels = (outInputChannel != null
                && (attrs.inputFeatures & INPUT_FEATURE_NO_INPUT_CHANNEL) == 0);
        if  (openInputChannels) {
            win.openInputChannel(outInputChannel);
        }

      //...
    if (reportNewConfig) {
        sendNewConfiguration(displayId);
    }

    Binder.restoreCallingIdentity(origId);

    return res;
}

代码很长重点看和我们的报错相关的，一个是type一个是token，我们先看type，因为token的值和type有关。

final int type = attrs.type;

attrs是LayoutParams类型的attrs

为什么是2呢，看下代码：

Window.java
private final WindowManager.LayoutParams mWindowAttributes = new WindowManager.LayoutParams();

WindowManager.java
public LayoutParams() {
    super(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT);
    type = TYPE_APPLICATION;
    format = PixelFormat.OPAQUE;
}

type = TYPE_APPLICATION，TYPE_APPLICATION=2。当type =2时parentWindow=null，因此token就是来自于attrs.token。

WindowToken token = displayContent.getWindowToken(hasParent ? parentWindow.mAttrs.token : attrs.token);

attrs又是LayoutParams。我们去看看attrs中的token又是怎么来的。我们需要往回找来到WindowManagerGlobal的addView方法。经过多次Debug调试，我们找到了token赋值的地方。

执行完 parentWindow.adjustLayoutParamsForSubWindow(wparams)后token被赋值。

如果传的是Activity parentWindow是有值的，如果传的是Application parentWindow则是null

Window.java

void adjustLayoutParamsForSubWindow(WindowManager.LayoutParams wp) {
    CharSequence curTitle = wp.getTitle();
    if (wp.type >= WindowManager.LayoutParams.FIRST_SUB_WINDOW &&
            wp.type <= WindowManager.LayoutParams.LAST_SUB_WINDOW) {
        if (wp.token == null) {
            View decor = peekDecorView();
            if (decor != null) {
                wp.token = decor.getWindowToken();
            }
        }
        if (curTitle == null || curTitle.length() == 0) {
            final StringBuilder title = new StringBuilder(32);
            if (wp.type == WindowManager.LayoutParams.TYPE_APPLICATION_MEDIA) {
                title.append("Media");
            } else if (wp.type == WindowManager.LayoutParams.TYPE_APPLICATION_MEDIA_OVERLAY) {
                title.append("MediaOvr");
            } else if (wp.type == WindowManager.LayoutParams.TYPE_APPLICATION_PANEL) {
                title.append("Panel");
            } else if (wp.type == WindowManager.LayoutParams.TYPE_APPLICATION_SUB_PANEL) {
                title.append("SubPanel");
            } else if (wp.type == WindowManager.LayoutParams.TYPE_APPLICATION_ABOVE_SUB_PANEL) {
                title.append("AboveSubPanel");
            } else if (wp.type == WindowManager.LayoutParams.TYPE_APPLICATION_ATTACHED_DIALOG) {
                title.append("AtchDlg");
            } else {
                title.append(wp.type);
            }
            if (mAppName != null) {
                title.append(":").append(mAppName);
            }
            wp.setTitle(title);
        }
    } else if (wp.type >= WindowManager.LayoutParams.FIRST_SYSTEM_WINDOW &&
            wp.type <= WindowManager.LayoutParams.LAST_SYSTEM_WINDOW) {
        // We don't set the app token to this system window because the life cycles should be
        // independent. If an app creates a system window and then the app goes to the stopped
        // state, the system window should not be affected (can still show and receive input
        // events).
        if (curTitle == null || curTitle.length() == 0) {
            final StringBuilder title = new StringBuilder(32);
            title.append("Sys").append(wp.type);
            if (mAppName != null) {
                title.append(":").append(mAppName);
            }
            wp.setTitle(title);
        }
    } else {
        if (wp.token == null) {
            wp.token = mContainer == null ? mAppToken : mContainer.mAppToken;
        }
        if ((curTitle == null || curTitle.length() == 0)
                && mAppName != null) {
            wp.setTitle(mAppName);
        }
    }
    if (wp.packageName == null) {
        wp.packageName = mContext.getPackageName();
    }
    if (mHardwareAccelerated ||
            (mWindowAttributes.flags & FLAG_HARDWARE_ACCELERATED) != 0) {
        wp.flags |= FLAG_HARDWARE_ACCELERATED;
    }
}

Window的类型

Window 的类型是 WindowManager 中 LayoutParams 类的 type 属性决定的。我们可以看到 Window 主要有三种类型。

  • APPLICATION_WINDOW：取值范围1-99

  • SUB_WINDOW：取值范围1000-1999

  • SYSTEM_WINDOW：取值范围2000-2999

public int type;

public static final int FIRST_APPLICATION_WINDOW = 1;
public static final int TYPE_BASE_APPLICATION   = 1;
public static final int TYPE_APPLICATION        = 2;
public static final int TYPE_APPLICATION_STARTING = 3;
public static final int TYPE_DRAWN_APPLICATION = 4;
public static final int LAST_APPLICATION_WINDOW = 99;


public static final int FIRST_SUB_WINDOW = 1000;
public static final int TYPE_APPLICATION_PANEL = FIRST_SUB_WINDOW;
public static final int TYPE_APPLICATION_MEDIA = FIRST_SUB_WINDOW + 1;
public static final int TYPE_APPLICATION_SUB_PANEL = FIRST_SUB_WINDOW + 2;
public static final int TYPE_APPLICATION_ATTACHED_DIALOG = FIRST_SUB_WINDOW + 3;
@UnsupportedAppUsage
public static final int TYPE_APPLICATION_MEDIA_OVERLAY  = FIRST_SUB_WINDOW + 4;
public static final int TYPE_APPLICATION_ABOVE_SUB_PANEL = FIRST_SUB_WINDOW + 5;
public static final int LAST_SUB_WINDOW = 1999;


public static final int FIRST_SYSTEM_WINDOW     = 2000;
public static final int TYPE_STATUS_BAR         = FIRST_SYSTEM_WINDOW;
public static final int TYPE_SEARCH_BAR         = FIRST_SYSTEM_WINDOW+1;
@Deprecated
public static final int TYPE_PHONE              = FIRST_SYSTEM_WINDOW+2;
@Deprecated
public static final int TYPE_SYSTEM_ALERT       = FIRST_SYSTEM_WINDOW+3;
public static final int TYPE_KEYGUARD           = FIRST_SYSTEM_WINDOW+4;
@Deprecated
public static final int TYPE_TOAST              = FIRST_SYSTEM_WINDOW+5;
@Deprecated
public static final int TYPE_SYSTEM_OVERLAY     = FIRST_SYSTEM_WINDOW+6;
@Deprecated
public static final int TYPE_PRIORITY_PHONE     = FIRST_SYSTEM_WINDOW+7;
public static final int TYPE_SYSTEM_DIALOG      = FIRST_SYSTEM_WINDOW+8;
public static final int TYPE_KEYGUARD_DIALOG    = FIRST_SYSTEM_WINDOW+9;
@Deprecated
public static final int TYPE_SYSTEM_ERROR       = FIRST_SYSTEM_WINDOW+10;
public static final int TYPE_INPUT_METHOD       = FIRST_SYSTEM_WINDOW+11;
public static final int TYPE_INPUT_METHOD_DIALOG= FIRST_SYSTEM_WINDOW+12;
public static final int TYPE_WALLPAPER          = FIRST_SYSTEM_WINDOW+13;
public static final int TYPE_STATUS_BAR_PANEL   = FIRST_SYSTEM_WINDOW+14;
@UnsupportedAppUsage
public static final int TYPE_SECURE_SYSTEM_OVERLAY = FIRST_SYSTEM_WINDOW+15;
public static final int TYPE_DRAG               = FIRST_SYSTEM_WINDOW+16;
public static final int TYPE_STATUS_BAR_SUB_PANEL = FIRST_SYSTEM_WINDOW+17;
public static final int TYPE_POINTER = FIRST_SYSTEM_WINDOW+18;
public static final int TYPE_NAVIGATION_BAR = FIRST_SYSTEM_WINDOW+19;
public static final int TYPE_VOLUME_OVERLAY = FIRST_SYSTEM_WINDOW+20;
public static final int TYPE_BOOT_PROGRESS = FIRST_SYSTEM_WINDOW+21;
public static final int TYPE_INPUT_CONSUMER = FIRST_SYSTEM_WINDOW+22;
public static final int TYPE_DREAM = FIRST_SYSTEM_WINDOW+23;
public static final int TYPE_NAVIGATION_BAR_PANEL = FIRST_SYSTEM_WINDOW+24;
@UnsupportedAppUsage
public static final int TYPE_DISPLAY_OVERLAY = FIRST_SYSTEM_WINDOW+26;
public static final int TYPE_MAGNIFICATION_OVERLAY = FIRST_SYSTEM_WINDOW+27;
public static final int TYPE_PRIVATE_PRESENTATION = FIRST_SYSTEM_WINDOW+30;
public static final int TYPE_VOICE_INTERACTION = FIRST_SYSTEM_WINDOW+31;
public static final int TYPE_ACCESSIBILITY_OVERLAY = FIRST_SYSTEM_WINDOW+32;
public static final int TYPE_VOICE_INTERACTION_STARTING = FIRST_SYSTEM_WINDOW+33;
public static final int TYPE_DOCK_DIVIDER = FIRST_SYSTEM_WINDOW+34;
public static final int TYPE_QS_DIALOG = FIRST_SYSTEM_WINDOW+35;
public static final int TYPE_SCREENSHOT = FIRST_SYSTEM_WINDOW + 36;
public static final int TYPE_PRESENTATION = FIRST_SYSTEM_WINDOW + 37;
public static final int TYPE_APPLICATION_OVERLAY = FIRST_SYSTEM_WINDOW + 38;
public static final int LAST_SYSTEM_WINDOW      = 2999;

public static final int INVALID_WINDOW_TYPE = -1;

AlertDialog 的 type 值是 2，PopupWindow 的 type 是 1000

parentWindow.adjustLayoutParamsForSubWindow(wparams)中的parentWindow其实就是WindowManagerImpl中的mParentWindow对象，这下就和WindowManager相关了，而WindowManager又是通过context获取的，所以产生了不同的表现，我们最后来分析为什么会有这种不同。再来回顾一下WindowManager的获取

Dialog(@NonNull Context context, @StyleRes int themeResId, boolean createContextThemeWrapper) {
    if (createContextThemeWrapper) {
        if (themeResId == Resources.ID_NULL) {
            final TypedValue outValue = new TypedValue();
            context.getTheme().resolveAttribute(R.attr.dialogTheme, outValue, true);
            themeResId = outValue.resourceId;
        }
        mContext = new ContextThemeWrapper(context, themeResId);
    } else {
        mContext = context;
    }

    mWindowManager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);

    final Window w = new PhoneWindow(mContext);
    mWindow = w;
    w.setCallback(this);
    w.setOnWindowDismissedCallback(this);
    w.setOnWindowSwipeDismissedCallback(() -> {
        if (mCancelable) {
            cancel();
        }
    });
    w.setWindowManager(mWindowManager, null, null);
    w.setGravity(Gravity.CENTER);

    mListenersHandler = new ListenersHandler(this);
}

通过上面的代码我们可以看到 mWindowManager 是通过context获取的，并把它设置给PhoneWindow。我们分别看看 WindowManager 是如何获取的

注意是在Dialog的show方法中的下面方法报的错，mWindowManager是Activity或Application的WindowManager

mWindowManager.addView(mDecor, l);
  • Activity Context
Activity.java

		@Override
    public Object getSystemService(@ServiceName @NonNull String name) {
        if (getBaseContext() == null) {
            throw new IllegalStateException(
                    "System services not available to Activities before onCreate()");
        }

        if (WINDOW_SERVICE.equals(name)) {
            return mWindowManager;
        } else if (SEARCH_SERVICE.equals(name)) {
            ensureSearchManager();
            return mSearchManager;
        }
        return super.getSystemService(name);
    }

再来看看mWindowManager是如何赋值的

Activity.java
  
		@UnsupportedAppUsage
    final void attach(Context context, ActivityThread aThread,
            Instrumentation instr, IBinder token, int ident,
            Application application, Intent intent, ActivityInfo info,
            CharSequence title, Activity parent, String id,
            NonConfigurationInstances lastNonConfigurationInstances,
            Configuration config, String referrer, IVoiceInteractor voiceInteractor,
            Window window, ActivityConfigCallback activityConfigCallback, IBinder assistToken) {
        attachBaseContext(context);

        mFragments.attachHost(null /*parent*/);

        mWindow = new PhoneWindow(this, window, activityConfigCallback);
        mWindow.setWindowControllerCallback(this);
        mWindow.setCallback(this);
        mWindow.setOnWindowDismissedCallback(this);
        mWindow.getLayoutInflater().setPrivateFactory(this);
        if (info.softInputMode != WindowManager.LayoutParams.SOFT_INPUT_STATE_UNSPECIFIED) {
            mWindow.setSoftInputMode(info.softInputMode);
        }
        if (info.uiOptions != 0) {
            mWindow.setUiOptions(info.uiOptions);
        }
        mUiThread = Thread.currentThread();

        mMainThread = aThread;
        mInstrumentation = instr;
        mToken = token;
        mAssistToken = assistToken;
        mIdent = ident;
        mApplication = application;
        mIntent = intent;
        mReferrer = referrer;
        mComponent = intent.getComponent();
        mActivityInfo = info;
        mTitle = title;
        mParent = parent;
        mEmbeddedID = id;
        mLastNonConfigurationInstances = lastNonConfigurationInstances;
        if (voiceInteractor != null) {
            if (lastNonConfigurationInstances != null) {
                mVoiceInteractor = lastNonConfigurationInstances.voiceInteractor;
            } else {
                mVoiceInteractor = new VoiceInteractor(voiceInteractor, this, this,
                        Looper.myLooper());
            }
        }

      	// 重点，这里的mToken是有值的
        mWindow.setWindowManager(
                (WindowManager)context.getSystemService(Context.WINDOW_SERVICE),
                mToken, mComponent.flattenToString(),
                (info.flags & ActivityInfo.FLAG_HARDWARE_ACCELERATED) != 0);
        if (mParent != null) {
            mWindow.setContainer(mParent.getWindow());
        }
      	// 给mWindowManager赋值
        mWindowManager = mWindow.getWindowManager();
        mCurrentConfig = config;

        mWindow.setColorMode(info.colorMode);

        setAutofillOptions(application.getAutofillOptions());
        setContentCaptureOptions(application.getContentCaptureOptions());
    }

Window.java
  
public void setWindowManager(WindowManager wm, IBinder appToken, String appName,
        boolean hardwareAccelerated) {
    mAppToken = appToken;
    mAppName = appName;
    mHardwareAccelerated = hardwareAccelerated;
    if (wm == null) {
        wm = (WindowManager)mContext.getSystemService(Context.WINDOW_SERVICE);
    }
    mWindowManager = ((WindowManagerImpl)wm).createLocalWindowManager(this);
}

public WindowManagerImpl createLocalWindowManager(Window parentWindow) {
  return new WindowManagerImpl(mContext, parentWindow);
}

// 注意这里可以看到parentWindow不为空，token也不为空
private WindowManagerImpl(Context context, Window parentWindow) {
	mContext = context;
	mParentWindow = parentWindow;
}

ActivityContext.getSystemService获取了windowManager，windowManager的mParentWindow就是Activity的PhoneWindow因此不为空。

WindowManagerImpl.java

@Override
public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
    applyDefaultToken(params);
    mGlobal.addView(view, params, mContext.getDisplay(), mParentWindow);
}

WindowManagerGlobal.java
public void addView(View view, ViewGroup.LayoutParams params,
        Display display, Window parentWindow) {
    if (view == null) {
        throw new IllegalArgumentException("view must not be null");
    }
    if (display == null) {
        throw new IllegalArgumentException("display must not be null");
    }
    if (!(params instanceof WindowManager.LayoutParams)) {
        throw new IllegalArgumentException("Params must be WindowManager.LayoutParams");
    }

    final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams) params;
    if (parentWindow != null) {
      	//parentWindow不为空会给token赋值
        parentWindow.adjustLayoutParamsForSubWindow(wparams);
    } else {
        // If there's no parent, then hardware acceleration for this view is
        // set from the application's hardware acceleration setting.
        final Context context = view.getContext();
        if (context != null
                && (context.getApplicationInfo().flags
                        & ApplicationInfo.FLAG_HARDWARE_ACCELERATED) != 0) {
            wparams.flags |= WindowManager.LayoutParams.FLAG_HARDWARE_ACCELERATED;
        }
    }
    // ...
}

看到这里基本可以分析出来了，我们再看看Application的

  • Application Context

Application获取WindowManager调用如下最终调的是ContextImpl的getSystemService

Application.java -> ContextWrapper.java -> ContextImpl.java

@Override
public Object getSystemService(String name) {
    return SystemServiceRegistry.getSystemService(this, name);
}

ContextImpl的调用栈如下图：

这里创建了WindowManager，其中的mParentWindow是null

ApplicationContext.getSystemService获取了windowManager，windowManager的mParentWindow为null

总结

至此整个流程分析完毕，我们也破案了。每种类型的Context都有自己的使命，大家用的时候要注意一下。

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