Window内部机制
Window.png
public final class WindowManagerImpl implements WindowManager {
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);
}
@Override
public void updateViewLayout(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
applyDefaultToken(params);
mGlobal.updateViewLayout(view, params);
}
@Override
public void removeView(View view) {
mGlobal.removeView(view, false);
}
@Override
public void removeViewImmediate(View view) {
mGlobal.removeView(view, true);
}
...
}
Window的添加过程
Window的添加过程需要通过WindowManager的addView来实现，WindowManager是一个接口， 真正实现是WindowManagerImpl类。可以发现，三大操作全部都是交给WindowManagerGlobal来处理，这种工作模式是典型的交接模式，将所有操作全部委托给WindowManagerGlobal来实现。
在WIndowManagerGlobal中，addView主要分为如下几步：
- 检查参数是否合法，如果是子Window还需要一些调整
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;
}
}
- 创建ViewRootImpl并将View添加到列表中
在WIndowManagerGlobal内部有这几个列表比较重要：
private final ArrayList<View> mViews = new ArrayList<View>();
private final ArrayList<ViewRootImpl> mRoots = new ArrayList<ViewRootImpl>();
private final ArrayList<WindowManager.LayoutParams> mParams =
new ArrayList<WindowManager.LayoutParams>();
private final ArraySet<View> mDyingViews = new ArraySet<View>();
mViews存储所有Window对应的View
mRoots存储所有Window对应的ViewRootImpl
mParams存储所有Window对应的布局参数
mDyingViews存储正在删除的View对象，即已经调用removeView但是还没删除完成的Window对象。
在addView中通过以下方式将Window一系列对象添加到列表：
root = new ViewRootImpl(view.getContext(), display);
view.setLayoutParams(wparams);
mViews.add(view);
mRoots.add(root);
mParams.add(wparams);
- 通过ViewRootImpl来更新界面并完成Window的添加过程
这个步骤由ViewRootImpl的setView完成。
// 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;
}
/**
* We have one child
*/
public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {
...
// Schedule the first layout -before- adding to the window
// manager, to make sure we do the relayout before receiving
// any other events from the system.
requestLayout();
...
try {
mOrigWindowType = mWindowAttributes.type;
mAttachInfo.mRecomputeGlobalAttributes = true;
collectViewAttributes();
res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
getHostVisibility(), mDisplay.getDisplayId(),
mAttachInfo.mContentInsets, mAttachInfo.mStableInsets,
mAttachInfo.mOutsets, mInputChannel);
} 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);
}
...
}
@Override
public void requestLayout() {
if (!mHandlingLayoutInLayoutRequest) {
checkThread();
mLayoutRequested = true;
scheduleTraversals();
}
}
//Session的内部addToDisplay实现
@Override
public int addToDisplay(IWindow window, int seq, WindowManager.LayoutParams attrs,
int viewVisibility, int displayId, Rect outContentInsets, Rect outStableInsets,
Rect outOutsets, InputChannel outInputChannel) {
return mService.addWindow(this, window, seq, attrs, viewVisibility, displayId,
outContentInsets, outStableInsets, outOutsets, outInputChannel);
}
通过WindowSession来完成Window的添加过程。mWindowSession的类型是IWinSession，是一个Binder对象，实现类是Session，就是说Window的添加过程是一次IPC调用。查看Session内部addToDisplay方法，得知Window的添加请求最终是WindowManagerService处理了，在WindowManagerService内部会为每一个应用保留一个单独的Session。
WIndow的删除过程
删除过程和添加过程一样是通过WindowManagerGlobal来实现的。
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);
}
}
先findViewLocked来查找待删除的view的索引，在调用removeViewLocked来删除。
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);
}
}
}
这里可以看出removeViewLocked是通过ViewRootImpl来完成删除的。
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;
}
删除View的接口有两种removeView()和removeViewImmediate()，对应的是异步删除和同步删除。在这里的die方法内部只是做了简单的判断，如果是异步删除则发送一个MSG_DIE的消息去消息队列让Handler处理并调用doDie()，如果是同步删除则直接调用doDie()。在doDie()内部会调用dispatchDetachedFromWindow()，真正删除View的逻辑就在这个方法内部实现。
dispatchDetachedFromWindow方法主要做四件事：
- 垃圾回收相关的工作，比如清除数据和消息、移除回调。
- 通过Session的remove方法删除Window：mWindowSession.remove(mWindow)，这同样是一个IPC过程，最终会调用WindowManagerService的removeWindow方法。
- 调用View的dispatchDetachedFromWindow方法，在内部会调用View的onDetachedFromWindow()以及onDetachedFromWindowInternal()。当View从Window移除时，会调用onDetachedFromWindow()这个方法，可以在里面做一些资源回收的工作，比如终止动画，停止线程等。
- 调用WindowManagerGlobal的doRemoveView方法刷新数据，包括mRoots、mParams以及mDyingViews，需要将当前Window所关联的这三类对象从列表删除。
Window的更新过程
这里还是一样看WindowManangerGobal中的updateViewLayout方法。
public void updateViewLayout(View view, ViewGroup.LayoutParams params) {
if (view == null) {
throw new IllegalArgumentException("view must not be null");
}
if (!(params instanceof WindowManager.LayoutParams)) {
throw new IllegalArgumentException("Params must be WindowManager.LayoutParams");
}
final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams)params;
view.setLayoutParams(wparams);
synchronized (mLock) {
int index = findViewLocked(view, true);
ViewRootImpl root = mRoots.get(index);
mParams.remove(index);
mParams.add(index, wparams);
root.setLayoutParams(wparams, false);
}
}
这里就是更新了View的LayoutParams并替换老的LayoutParams，接着更新ViewRootImpl中的LayoutParams，这一步通过ViewRootImpl的setLayoutParams来实现。在ViewRootImpl中会通过scheduleTraversals方法来对View重新布局，包括测量、布局、重绘。除了View的重绘以外，ViewRootImpl还会通过WindowSession来更新Window的视图，这个过程最终是由WindowManagerService的relayoutWindow()来实现，同样是一个IPC过程。
