从系统角度理解Android的界面绘制
任何一个操作系统要实现界面绘制，都需要处理好应用层、系统层和硬件层的分工协作：
应用层负责定义画面的内容
系统层负责综合整个屏幕的画面并保证流畅
硬件层负责把数据输出到显示设备上
1、view是如何被添加到屏幕上
1、创建顶层布局容器DecorView
2、在顶层布局中加载基础布局ViewGroup
3、将ContentView添加到基础布局中的FramLayout中
Activity
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.add_item_confirmation_activity);
}
public void setContentView(@LayoutRes int layoutResID) {
getWindow().setContentView(layoutResID);
initWindowDecorActionBar();
}
PhoneWindow
@Override
public void setContentView(int layoutResID) {
if (mContentParent == null) {
installDecor(); // 1
} else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
.removeAllViews();
}
if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
final Scene newScene = Scene.getSceneForLayout(mContentParent, layoutResID,
getContext());
transitionTo(newScene);
} else {
mLayoutInflater.inflate(layoutResID, mContentParent);// 2
}
}
private void installDecor() {
mForceDecorInstall = false;
if (mDecor == null) {
mDecor = generateDecor(-1);// 1 生成一个 new DecorView
...
} else {
mDecor.setWindow(this);
}
if (mContentParent == null) {
mContentParent = generateLayout(mDecor);// 2 R.id.content
...
}
}
protected ViewGroup generateLayout(DecorView decor) {
...
if ((features & (1 << FEATURE_ACTION_MODE_OVERLAY)) != 0) {
layoutResource = R.layout.screen_simple_overlay_action_mode;
} else {
// Embedded, so no decoration is needed.
layoutResource = R.layout.screen_simple; // 1 以此为例
// System.out.println("Simple!");
}
mDecor.startChanging();
mDecor.onResourcesLoaded(mLayoutInflater, layoutResource);
// 2 com.android.internal.R.id.content
ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
if (contentParent == null) {
throw new RuntimeException("Window couldn't find content container view");
}
mDecor.finishChanging();
return contentParent;
}
\Android\sdk\platforms\android-30\data\res\layout
2、view的绘制流程
1、绘制入口 ActivityThread.handleResumeActivity -->WindowManagerImpl.addView(decorView,layoutParams) -->WindowManagerGlobal.addView()
2、绘制的类及方法 ViewRootImpl.setView(decorView,layoutParams,parentView) -->ViewRootImpl.requestLayout-->scheduleTraversals -->doTraversal-->performTraversals
3、绘制三大步骤 测量：ViewRootImpl.performMeasure 布局：ViewRootImpl.performLayout 绘制：ViewRootImpl.performDraw
@Override
public void handleResumeActivity(IBinder token,
boolean finalStateRequest, boolean isForward,String reason) {
// 1
final ActivityClientRecord r = performResumeActivity(token, finalStateRequest, reason);
if (r == null) {
// We didn't actually resume the activity, so skipping any follow-up actions.
return;
}
...
if (r.window == null && !a.mFinished && willBeVisible) {
r.window = r.activity.getWindow();
View decor = r.window.getDecorView();
decor.setVisibility(View.INVISIBLE);
ViewManager wm = a.getWindowManager();// 2
WindowManager.LayoutParams l = r.window.getAttributes();
a.mDecor = decor;
l.type = WindowManager.LayoutParams.TYPE_BASE_APPLICATION;
l.softInputMode |= forwardBit;
if (r.mPreserveWindow) {
a.mWindowAdded = true;
r.mPreserveWindow = false;
ViewRootImpl impl = decor.getViewRootImpl();
if (impl != null) {
impl.notifyChildRebuilt();
}
}
if (a.mVisibleFromClient) {
if (!a.mWindowAdded) {
a.mWindowAdded = true;
wm.addView(decor, l);
} else {
// The activity will get a callback for this {@link LayoutParams} change
// earlier. However, at that time the decor will not be set (this is set
// in this method), so no action will be taken. This call ensures the
// callback occurs with the decor set.
a.onWindowAttributesChanged(l);
}
}
}
r.nextIdle = mNewActivities;
mNewActivities = r;
if (localLOGV) Slog.v(TAG, "Scheduling idle handler for " + r);
Looper.myQueue().addIdleHandler(new Idler());
}
Activity
mWindowManager = mWindow.getWindowManager();
Window
mWindowManager = ((WindowManagerImpl)wm).createLocalWindowManager(this);
WindowManagerImpl
@Override
public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
applyDefaultToken(params);
mGlobal.addView(view, params, mContext.getDisplayNoVerify(), mParentWindow,
mContext.getUserId());
}
public void addView(View view, ViewGroup.LayoutParams params,
Display display, Window parentWindow, int userId) {
...
ViewRootImpl root;
View panelParentView = null;
synchronized (mLock) {
root = new ViewRootImpl(view.getContext(), display); //1
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, userId); //2
} catch (RuntimeException e) {
// BadTokenException or InvalidDisplayException, clean up.
if (index >= 0) {
removeViewLocked(index, true);
}
throw e;
}
}
}
ViewRootImpl
public void setView(View view, WindowManager.LayoutParams attrs,
View panelParentView,int userId) {
synchronized (this) {
if (mView == null) {
mView = view;
...
// 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(); //1
...
}
}
}
@Override
public void requestLayout() {
if (!mHandlingLayoutInLayoutRequest) {
checkThread();
mLayoutRequested = true;
scheduleTraversals();
}
}
void checkThread() {
if (mThread != Thread.currentThread()) {
throw new CalledFromWrongThreadException(
"Only the original thread that created a view hierarchy can touch its views.");
}
}
@UnsupportedAppUsage
void scheduleTraversals() {
if (!mTraversalScheduled) {
mTraversalScheduled = true;
mTraversalBarrier = mHandler.getLooper().getQueue().postSyncBarrier();
mChoreographer.postCallback(
Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null); //1
notifyRendererOfFramePending();
pokeDrawLockIfNeeded();
}
}
final class TraversalRunnable implements Runnable {
@Override
public void run() {
doTraversal();
}
}
void doTraversal() {
if (mTraversalScheduled) {
mTraversalScheduled = false;
mHandler.getLooper().getQueue().removeSyncBarrier(mTraversalBarrier); //1
if (mProfile) {
Debug.startMethodTracing("ViewAncestor");
}
performTraversals(); //2
if (mProfile) {
Debug.stopMethodTracing();
mProfile = false;
}
}
}
private void performTraversals() {
...
// Ask host how big it wants to be
performMeasure(childWidthMeasureSpec, childHeightMeasureSpec);
...
performLayout(lp, mWidth, mHeight);
...
performDraw();
}
