可以知道的是 Android 中的所有视图都是通过 Window 来呈现的，Window 是 View 的管理者。
向 Window 添加 View 是通过 WindowManager 来实现的。
WindowManager 是一个接口，并且继承自 ViewManager。
关于 ViewManager
public interface ViewManager{
public void addView(View view, ViewGroup.LayoutParams params);
public void updateViewLayout(View view, ViewGroup.LayoutParams params);
public void removeView(View vaiew);
}
可以看到只有三个方法，添加、更新、删除 View。
WindowManager 也是一个接口，它的实现类是 WindowManagerImpl。查看 WindowManagerImpl
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);
}
}
可以看到 WindowManagerImpl 也没有实现视图的添加、更新、删除，而是交给了 WindowManagerGlobal 来处理，继续追踪。找到 WindowManagerGlobal.addView()
public void addView(View view, ViewGroup.LayoutParams params,
Display display, Window parentWindow) {
// 首先检查合法性
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");
}
// 检查父级 View 是否存在
final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams) params;
if (parentWindow != null) {
// adjustLayoutParamsForSubWindow 从字面意思是调整窗口布局参数
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);
}
// 检测是否已经存在这个 view
int index = findViewLocked(view, false);
if (index >= 0) {
// 如果已经存在但是是快要移除的 view 就 移除它
if (mDyingViews.contains(view)) {
// Don't wait for MSG_DIE to make it's way through root's queue.
mRoots.get(index).doDie();
} else {
// 否则抛出异常
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 {
// 最终是通过 ViewRootImpl 的 setView 方法来添加View
root.setView(view, wparams, panelParentView);
} catch (RuntimeException e) {
// BadTokenException or InvalidDisplayException, clean up.
synchronized (mLock) {
final int index = findViewLocked(view, false);
if (index >= 0) {
removeViewLocked(index, true);
}
}
throw e;
}
}
经过上面的分析可以知道，最终是通过 ViewRootImpl.setView() 方法来添加
public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {
...
// 通过requestLayout来刷新视图并完成绘制
requestLayout();
...
collectViewAttributes();
// 通过mWindowSession.addToDisplay 来进行显示
res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
getHostVisibility(), mDisplay.getDisplayId(),
mAttachInfo.mContentInsets, mAttachInfo.mStableInsets,
mAttachInfo.mOutsets, mInputChannel);
...
}
在 ViewRootImpl 中 mWindowSession 初始化
IWindowSession mWindowSession = WindowManagerGlobal.getWindowSession();
IWindowSession 是一个 Binder 对象，所以在添加过程中进行了 IPC 调用
public static IWindowSession getWindowSession() {
synchronized (WindowManagerGlobal.class) {
...
// 获取 WindowManagerService
IWindowManager windowManager = getWindowManagerService();
sWindowSession = windowManager.openSession()
...
}
return sWindowSession;
}
}
//WindowManagerService.openSession
@Override
public IWindowSession openSession(IWindowSessionCallback callback, IInputMethodClient client,
IInputContext inputContext) {
if (client == null) throw new IllegalArgumentException("null client");
if (inputContext == null) throw new IllegalArgumentException("null inputContext");
Session session = new Session(this, callback, client, inputContext);
return session;
}
可以看到上面的 mWindowSession 对象真正实现是一个 Session。那就可以继续追踪到 Session.addToDisplay()
final WindowManagerService mService;
@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);
}
通过上面的代码可以看到，最终是通过 WindowManagerService.addWindow 来进行添加。至于 WindowManagerService 怎么处理的暂时不做深入了，太长了这个方法...