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前言
我们之前说过Activity的启动流程,我们知道ActivityThread在执行完performLaunchActivity后会执行handleResumeActivity这个方法,handleResumeActivity方法中先调用了performResumeActivity这个方法，而performResumeActivity中就会去回调Activity中的onResume方法，在执行完performResumeActivity后，又做了很多事，也就是我们这篇要分析的
handleResumeActivity
public void handleResumeActivity(IBinder token, boolean finalStateRequest, boolean isForward,
String reason) {
// If we are getting ready to gc after going to the background, well
// we are back active so skip it.
unscheduleGcIdler();
mSomeActivitiesChanged = true;
// TODO Push resumeArgs into the activity for consideration
final ActivityClientRecord r = performResumeActivity(token, finalStateRequest, reason);
...
//设置WindowManager和DecorView的关系
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();
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;
// Normally the ViewRoot sets up callbacks with the Activity
// in addView->ViewRootImpl#setView. If we are instead reusing
// the decor view we have to notify the view root that the
// callbacks may have changed.
ViewRootImpl impl = decor.getViewRootImpl();
if (impl != null) {
impl.notifyChildRebuilt();
}
}
if (a.mVisibleFromClient) {
if (!a.mWindowAdded) {
a.mWindowAdded = true;
//把DecorView加入到WindowManager当中
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);
}
}
...
}
主要看这一段代码
if (a.mVisibleFromClient) {
if (!a.mWindowAdded) {
a.mWindowAdded = true;
//把DecorView加入到WindowManager当中
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);
}
}
这个wm是WindowManager,WindowManager是一个接口,所以我们需要去它的实现类WindowManagerImpl看下这个方法
@Override
public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
applyDefaultToken(params);
mGlobal.addView(view, params, mContext.getDisplay(), mParentWindow);
}
这个mGlobal是WindowManagerGlobal,addView会执行到WindowManagerGlobal的addView方法,我们点进去看下这个方法(代码很长,只贴出主要代码)
public void addView(View view, ViewGroup.LayoutParams params,
Display display, Window parentWindow) {
...
ViewRootImpl root;
View panelParentView = null;
...
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;
}
}
}
这里我们发现会创建一个ViewRootImpl,并且会调用它的setView方法.我们点进去看下这个方法(代码也很长,看主要代码)
/**
* We have one child
*/
public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {
synchronized (this) {
...
requestLayout();
...
}
主要就是这个requestLayout方法
@Override
public void requestLayout() {
if (!mHandlingLayoutInLayoutRequest) {
checkThread();
mLayoutRequested = true;
scheduleTraversals();
}
}
OK,界面绘制从这里开始了
开始绘制
首先我们看下checkThread();这个方法
void checkThread() {
if (mThread != Thread.currentThread()) {
throw new CalledFromWrongThreadException(
"Only the original thread that created a view hierarchy can touch its views.");
}
}
检查线程,要求界面绘制必须在主线程中进行更新.mThread就是主线程，所以如果当前运行的线程不是主线程，那么就直接报这个异常;
mLayoutRequested设置成true，避免收到重复的layout请求;
接下来就是真正的界面绘制的,我们看下这个scheduleTraversals方法
@UnsupportedAppUsage
void scheduleTraversals() {
if (!mTraversalScheduled) {
mTraversalScheduled = true;
mTraversalBarrier = mHandler.getLooper().getQueue().postSyncBarrier();
mChoreographer.postCallback(
Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);
if (!mUnbufferedInputDispatch) {
scheduleConsumeBatchedInput();
}
notifyRendererOfFramePending();
pokeDrawLockIfNeeded();
}
}
主要就是这段代码:
mChoreographer.postCallback(
Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);
调用了Choreographer中的方法.这个Choreographer用来控制同步处理输入(Input)、动画(Animation)、绘制(Draw)三个UI操作(UI显示的时候每一帧要完成的事情只有这三种)。其内部维护着一个Queue,使用者可以通过postXXX来把一些列待运行的UI操作放到Queue中。这些事件会在Choreographer接收显示系统的时间脉冲(垂直同步信号-VSync信号)后执行这些操作。
我们接着看下这个mTraversalRunnable
final class TraversalRunnable implements Runnable {
@Override
public void run() {
doTraversal();
}
}
void doTraversal() {
if (mTraversalScheduled) {
mTraversalScheduled = false;
mHandler.getLooper().getQueue().removeSyncBarrier(mTraversalBarrier);
if (mProfile) {
Debug.startMethodTracing("ViewAncestor");
}
performTraversals();
if (mProfile) {
Debug.stopMethodTracing();
mProfile = false;
}
}
}
最终会调用performTraversals方法，接下来就开始View的measure了,会执行
// Ask host how big it wants to be
windowSizeMayChange |= measureHierarchy(host, lp, res,
desiredWindowWidth, desiredWindowHeight);
看下注释我们也该差不多分析出来这个方法主要是用来测量的,measureHierarchy中的第一个参数host就是DecordeView对象，后面两个参数是屏幕的宽和高，然后根据lp，也就是LayoutParams的属性，例如lp.width，lp.height来求出View的宽和高
我们点进去看下
private boolean measureHierarchy(final View host, final WindowManager.LayoutParams lp,
final Resources res, final int desiredWindowWidth, final int desiredWindowHeight) {
int childWidthMeasureSpec;
int childHeightMeasureSpec;
boolean windowSizeMayChange = false;
if (DEBUG_ORIENTATION || DEBUG_LAYOUT) Log.v(mTag,
"Measuring " + host + " in display " + desiredWindowWidth
+ "x" + desiredWindowHeight + "...");
boolean goodMeasure = false;
if (lp.width == ViewGroup.LayoutParams.WRAP_CONTENT) {
// On large screens, we don't want to allow dialogs to just
// stretch to fill the entire width of the screen to display
// one line of text. First try doing the layout at a smaller
// size to see if it will fit.
final DisplayMetrics packageMetrics = res.getDisplayMetrics();
res.getValue(com.android.internal.R.dimen.config_prefDialogWidth, mTmpValue, true);
int baseSize = 0;
if (mTmpValue.type == TypedValue.TYPE_DIMENSION) {
baseSize = (int)mTmpValue.getDimension(packageMetrics);
}
if (DEBUG_DIALOG) Log.v(mTag, "Window " + mView + ": baseSize=" + baseSize
+ ", desiredWindowWidth=" + desiredWindowWidth);
if (baseSize != 0 && desiredWindowWidth > baseSize) {
childWidthMeasureSpec = getRootMeasureSpec(baseSize, lp.width);
childHeightMeasureSpec = getRootMeasureSpec(desiredWindowHeight, lp.height);
performMeasure(childWidthMeasureSpec, childHeightMeasureSpec);
if (DEBUG_DIALOG) Log.v(mTag, "Window " + mView + ": measured ("
+ host.getMeasuredWidth() + "," + host.getMeasuredHeight()
+ ") from width spec: " + MeasureSpec.toString(childWidthMeasureSpec)
+ " and height spec: " + MeasureSpec.toString(childHeightMeasureSpec));
if ((host.getMeasuredWidthAndState()&View.MEASURED_STATE_TOO_SMALL) == 0) {
goodMeasure = true;
} else {
// Didn't fit in that size... try expanding a bit.
baseSize = (baseSize+desiredWindowWidth)/2;
if (DEBUG_DIALOG) Log.v(mTag, "Window " + mView + ": next baseSize="
+ baseSize);
childWidthMeasureSpec = getRootMeasureSpec(baseSize, lp.width);
performMeasure(childWidthMeasureSpec, childHeightMeasureSpec);
if (DEBUG_DIALOG) Log.v(mTag, "Window " + mView + ": measured ("
+ host.getMeasuredWidth() + "," + host.getMeasuredHeight() + ")");
if ((host.getMeasuredWidthAndState()&View.MEASURED_STATE_TOO_SMALL) == 0) {
if (DEBUG_DIALOG) Log.v(mTag, "Good!");
goodMeasure = true;
}
}
}
}
if (!goodMeasure) {
childWidthMeasureSpec = getRootMeasureSpec(desiredWindowWidth, lp.width);
childHeightMeasureSpec = getRootMeasureSpec(desiredWindowHeight, lp.height);
performMeasure(childWidthMeasureSpec, childHeightMeasureSpec);
if (mWidth != host.getMeasuredWidth() || mHeight != host.getMeasuredHeight()) {
windowSizeMayChange = true;
}
}
if (DBG) {
System.out.println("======================================");
System.out.println("performTraversals -- after measure");
host.debug();
}
return windowSizeMayChange;
}
主要就会执行performMeasure方法
private void performMeasure(int childWidthMeasureSpec, int childHeightMeasureSpec) {
if (mView == null) {
return;
}
Trace.traceBegin(Trace.TRACE_TAG_VIEW, "measure");
try {
mView.measure(childWidthMeasureSpec, childHeightMeasureSpec);
} finally {
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
}
}
我们可以注意到childWidthMeasureSpec和childHeightMeasureSpec是通过一个叫getRootMeasureSpec的方法获取的,我们点进去看下这个方法
/**
* Figures out the measure spec for the root view in a window based on it's
* layout params.
*
* @param windowSize
* The available width or height of the window
*
* @param rootDimension
* The layout params for one dimension (width or height) of the
* window.
*
* @return The measure spec to use to measure the root view.
*/
private static int getRootMeasureSpec(int windowSize, int rootDimension) {
int measureSpec;
switch (rootDimension) {
case ViewGroup.LayoutParams.MATCH_PARENT:
// Window can't resize. Force root view to be windowSize.
measureSpec = MeasureSpec.makeMeasureSpec(windowSize, MeasureSpec.EXACTLY);
break;
case ViewGroup.LayoutParams.WRAP_CONTENT:
// Window can resize. Set max size for root view.
measureSpec = MeasureSpec.makeMeasureSpec(windowSize, MeasureSpec.AT_MOST);
break;
default:
// Window wants to be an exact size. Force root view to be that size.
measureSpec = MeasureSpec.makeMeasureSpec(rootDimension, MeasureSpec.EXACTLY);
break;
}
return measureSpec;
}
这里有一个MeasureSpec,我们先简单分析下这个MeasureSpec:
MeasureSpec是一个32位整数，由SpecMode和SpecSize两部分组成，其中高2位为SpecMode，低30位为SpecSize。SpecMode为测量模式，SpecSize为相应测量模式下的测量尺寸。View（包括普通View和ViewGroup）的SpecMode由本View的LayoutParams结合父View的MeasureSpec生成。例如:
00 000000 00000000 00000000 00000000
SpecMode的取值可为以下三种：
MeasureSpec.EXACTLY，对应LayoutParams.MATCH_PARENT，表示后View需要一个确切的尺寸MeasureSpec.AT_MOST，对应LayoutParams.WRAP_CONTENT，表示View的尺寸是自适应的，但是不能超过给定的SpecSizeMeasureSpec.UNSPECIFIED,这个在View的measure过程中没有用到，父容器不对View作任何限制，系统内部使用。
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