Window和WindowManager（二）
Window的刪除過程
上篇文章我們講到了Window的新增過程，接下來我們來分析Window的刪除過程。還是和新增一樣，首先通過WindowManagerImpl這個物件呼叫removeView方法。
@Override
public void removeView(View view) {
mGlobal.removeView(view, false);
}
接著通過 WindowManagerGlobal mGlobal 物件呼叫removeView方法。我們來看WindowManagerGlobal 中的removeView方法：
public void removeView(View view, boolean immediate) {
if (view == null) {
throw new IllegalArgumentException("view must not be null");
}
synchronized (mLock) {
int index = findViewLocked(view, true);
View curView = mRoots.get(index).getView();
removeViewLocked(index, immediate);
if (curView == view) {
return;
}
throw new IllegalStateException("Calling with view " + view
+ " but the ViewAncestor is attached to " + curView);
}
}
我們來看核心實現，首先從mViews集合獲取需要刪除View的索引，因為在新增View的時候，把View新增到了mViews這個集合。
int index = findViewLocked(view, true);
private int findViewLocked(View view, boolean required) {
final int index = mViews.indexOf(view);
if (required && index < 0) {
throw new IllegalArgumentException("View=" + view + " not attached to window manager");
}
return index;
}
通過索引呼叫removeViewLocked方法，刪除該View
removeViewLocked(index, immediate);
private void removeViewLocked(int index, boolean immediate) {
ViewRootImpl root = mRoots.get(index);
View view = root.getView();
if (view != null) {
InputMethodManager imm = InputMethodManager.getInstance();
if (imm != null) {
imm.windowDismissed(mViews.get(index).getWindowToken());
}
}
boolean deferred = root.die(immediate);
if (view != null) {
view.assignParent(null);
if (deferred) {
mDyingViews.add(view);
}
}
}
我們看上面的原始碼。首先通過該View對應的索引，獲取對應的ViewRootImpl類，我們知道每個Window和View多是通過ViewRootImpl建立連線的，對Window的操作，其實就是通過ViewRootImpl來操作的。每個Window都會有對應的ViewRootImpl類。拿到該View對應的ViewRootImpl也就是該Window對應的ViewRootImpl類之後，呼叫die方法進行刪除操作。
boolean deferred = root.die(immediate);
我們來看下die方法的實現，
/**
* @param immediate True, do now if not in traversal. False, put on queue and do later.
* @return True, request has been queued. False, request has been completed.
*/
boolean die(boolean immediate) {
// Make sure we do execute immediately if we are in the middle of a traversal or the damage
// done by dispatchDetachedFromWindow will cause havoc on return.
if (immediate && !mIsInTraversal) {
doDie();
return false;
}
if (!mIsDrawing) {
destroyHardwareRenderer();
} else {
Log.e(mTag, "Attempting to destroy the window while drawing!\n" +
"window=" + this + ", title=" + mWindowAttributes.getTitle());
}
mHandler.sendEmptyMessage(MSG_DIE);
return true;
}
在這個方法中，有一個immediate引數，表示非同步刪除還是同步刪除，如果是同步刪除，直接呼叫doDie(）方法。如果是非同步刪除，傳送一個訊息 mHandler.sendEmptyMessage(MSG_DIE);然後呼叫doDiew()方法。因此，刪除的核心方法都在doDie()中。我們來看下doDie()方法的實現
void doDie() {
checkThread();
if (LOCAL_LOGV) Log.v(mTag, "DIE in " + this + " of " + mSurface);
synchronized (this) {
if (mRemoved) {
return;
}
mRemoved = true;
if (mAdded) {
dispatchDetachedFromWindow();
}
if (mAdded && !mFirst) {
destroyHardwareRenderer();
if (mView != null) {
int viewVisibility = mView.getVisibility();
boolean viewVisibilityChanged = mViewVisibility != viewVisibility;
if (mWindowAttributesChanged || viewVisibilityChanged) {
// If layout params have been changed, first give them
// to the window manager to make sure it has the correct
// animation info.
try {
if ((relayoutWindow(mWindowAttributes, viewVisibility, false)
& WindowManagerGlobal.RELAYOUT_RES_FIRST_TIME) != 0) {
mWindowSession.finishDrawing(mWindow);
}
} catch (RemoteException e) {
}
}
mSurface.release();
}
}
mAdded = false;
}
WindowManagerGlobal.getInstance().doRemoveView(this);
}
在doDie()方法中，刪除的核心實現通過dispatchDetachedFromWindow();來完成。
void dispatchDetachedFromWindow() {
if (mView != null && mView.mAttachInfo != null) {
mAttachInfo.mTreeObserver.dispatchOnWindowAttachedChange(false);
mView.dispatchDetachedFromWindow();
}
mAccessibilityInteractionConnectionManager.ensureNoConnection();
mAccessibilityManager.removeAccessibilityStateChangeListener(
mAccessibilityInteractionConnectionManager);
mAccessibilityManager.removeHighTextContrastStateChangeListener(
mHighContrastTextManager);
removeSendWindowContentChangedCallback();
destroyHardwareRenderer();
setAccessibilityFocus(null, null);
mView.assignParent(null);
mView = null;
mAttachInfo.mRootView = null;
mSurface.release();
if (mInputQueueCallback != null && mInputQueue != null) {
mInputQueueCallback.onInputQueueDestroyed(mInputQueue);
mInputQueue.dispose();
mInputQueueCallback = null;
mInputQueue = null;
}
if (mInputEventReceiver != null) {
mInputEventReceiver.dispose();
mInputEventReceiver = null;
}
try {
mWindowSession.remove(mWindow);
} catch (RemoteException e) {
}
// Dispose the input channel after removing the window so the Window Manager
// doesn't interpret the input channel being closed as an abnormal termination.
if (mInputChannel != null) {
mInputChannel.dispose();
mInputChannel = null;
}
mDisplayManager.unregisterDisplayListener(mDisplayListener);
unscheduleTraversals();
}
在dispatchDetachedFromWindow方法中主要完成以下這些操作。
（1）呼叫View的dispatchDetachedFromWindow();方法，做一些資源回收的工作，比如終止動畫，停止執行緒等。
（2）垃圾回收，比如清楚資料和訊息，移除回撥
（3）第三點比較重要，也是實現刪除Window的真正實現， mWindowSession.remove(mWindow);在上篇文章我們知道，mWindowSession是一個Binder物件，這裡是一個IPC機制，通過跨程序通訊，把刪除Window的操作交給了WindowManagerService進行刪除。
（4）呼叫WindowManagerGlobal.getInstance().doRemoveView(this);把當前儲存的刪除的View 列表進行移除重新整理。
以上就是Window的刪除大概的流程，我們做下小結：
我們知道刪除Window
1.首先交給WindowManagerGlobal 的removie方法，這個方法是為了拿到需要刪除的View的索引，再通過該索引拿到對應的ViewRootImpl物件，
2.然後刪除Window的實現交給了ViewRootImpl來完成。通過呼叫die方法。
3.最後的核心刪除操作就是和新增Window類似，通過Binde物件mWindowSession實現跨程序通訊，把最終的刪除操作交給了WindowManagerService完成，刪除完成之後，再對一些垃圾的回收，資料的清除，回撥的移除，以及刪除列表的更新。
Window的更新過程
我們上面分別介紹了Window的新增以及刪除過程，下面我們來介紹，Window的更新過程。
還是一樣首先從WindowImpl的updateViewLayout
@Override
public void updateViewLayout(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
applyDefaultToken(params);
mGlobal.updateViewLayout(view, params);
}