Android自定义一个view ViewRootImpl绘制流程示例

Android如何自定义一个view ViewRootImpl绘制流程

1、自定义属性

在res/values/attrs.xml文件里定义一个declare-styleable name：自定义view的名字

<resources>
   <declare-styleable name="CustomView">
       <attr name="background" format="color"/> //定义属性：名称 + 格式类型---颜色、尺寸、整形、字符串类型
       <attr name="size" format="dimension"/>
       <attr name="AttrFirst" format="integer"/>
       <attr name="AttrSecond" format="string"/>
   </declare-styleable>
</resources>

2、在res/layout/activity_main.xml文件里使用自定义view

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
   xmlns:android="http://schemas.android.com/apk/res/android"
   xmlns:tools="http://schemas.android.com/tools"
   xmlns:custom="http://schemas.android.com/apk/res-auto" // 自定义的命名空间
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   android:orientation="vertical"
   tools:context="com.example.custom.MainActivity">
   <com.example.custom.CustomView
       android:id="@+id/custom_view"
       android:layout_width="100dp"
       android:layout_height="100dp"
       custom:background="@color/colorPrimary"
       custom:size="20dp"
       custom:AttrFirst="1"
       custom:AttrSecond="CustomView"/>
</LinearLayout>

3、构造CustomView名称的view，读取自定义属性

//通过AttributeSet直接获取

public CustomView(Context context, AttributeSet attrs) {
   super(context, attrs);
   int n = attrs.getAttributeCount(); //获得自定义view的属性数量
   for (int i =0; i < n; i++) {
      Log.d("CustomView", "attrs No " + i + ", name: " + attrs.getAttributeName(i) + ", value: " + attrs.getAttributeValue(i));
   }
   int custon_background = attrs.getAttributeIntValue("http://schemas.android.com/apk/res-auto", "background", Color.BLUE);
   int custom_size = attrs.getAttributeIntValue("http://schemas.android.com/apk/res-auto", "size", 10);
   int AttrFirst = attrs.getAttributeIntValue("http://schemas.android.com/apk/res-auto", "AttrFirst", 100));
   String AttrSecond = attrs.getAttributeValue("http://schemas.android.com/apk/res-auto", "AttrSecond"));
}

//getAttributeName来获取对应index处的属性名称，以sting返回。

//getAttributeValue来获取相应index处属性的值，以string返回。

//getAttributeIntValue来获取相应attribute属性的值

public String getAttributeValue(String namespace, String attribute);

public int getAttributeIntValue(String namespace, String attribute, int defaultValue);

namespace代表自定义属性的命名空间（与xml中的使用方法相同）

public class CustomView extends View {
   private Paint mPaint;
   private int mHeight;
   private int mWidth;
   private int custom_size;
   private float scale = 1f;
   private final int SIZE = 30;
   public CustomView(Context context) {
       this(context, null);
   }
   public CustomView(Context context, AttributeSet attrs) {
       this(context, attrs, 0);
   }
   public CustomView(Context context, AttributeSet attrs, int defStyleAttr) {
       super(context, attrs, defStyleAttr);
       TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.CustomView, defStyleAttr, R.style.AppTheme); //通过obtainStyledAttributes()方法获取属性值
       int custon_background = a.getColor(R.styleable.CustomView_background, Color.BLUE);
       custom_size = a.getDimensionPixelSize(R.styleable.CustomView_size, 10);
       int AttrFirst = arr.getInt(R.styleable.CustomView_AttrFirst, 100);
       String AttrSecond = arr.getString(R.styleable.CustomView_AttrSecond);
       a.recycle();
       mPaint = new Paint();
       mPaint.setColor(custom_background);
       mPaint.setAntiAlias(true);
       mPaint.setStyle(Paint.Style.FILL);
   }
   @Override
   protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { //计算出实际的高(mMeasuredHeight)和宽(mMeasureWidth)传入setMeasuredDimension()方法完成单个View的测量
       int widthMode = MeasureSpec.getMode(widthMeasureSpec);
       int widthSize = MeasureSpec.getSize(widthMeasureSpec);
       int heightMode = MeasureSpec.getMode(heightMeasureSpec);
       int heightSize = MeasureSpec.getSize(heightMeasureSpec);
       int measuredHeight, measuredWidth;
       if (widthMode == MeasureSpec.EXACTLY) {
           measuredWidth = widthSize;
       } else {
           measuredWidth = SIZE;
       }
       if (heightMode == MeasureSpec.EXACTLY) {
           measuredHeight = heightSize;
       } else {
           measuredHeight = SIZE;
       }
       setMeasuredDimension(measuredWidth, measuredHeight);
   }
   @Override
   protected void onLayout(boolean changed, int left, int top, int right, int bottom) { //onLayout决定具体View的大小和位置, 对当前视图和其所有子View设置它们在父视图中具体位置
       super.onLayout(changed, left, top, right, bottom);
       mHeight = getHeight(); //getWidth,和getLeft等这些函数都是View相对于其父View的位置。而getMeasuredWidth,getMeasuredHeight是测量后该View的实际值
       mWidth = getWidth();
   }
   @Override
   protected void onDraw(Canvas canvas) {
       canvas.drawCircle(mWidth/2, mHeight/2, custom_size * scale, mPaint);
   }
   private ValueAnimator mAnimator;
   public void startAnimation() {
       mAnimator = ValueAnimator.ofFloat(1, 2);
       mAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
           @Override
           public void onAnimationUpdate(ValueAnimator animation) {
               scale = (float) animation.getAnimatedValue();
               postInvalidate();
           }
       });
       mAnimator.setRepeatCount(-1); //重复次数，-1表示无限循环  
       mAnimator.setRepeatMode(ValueAnimator.REVERSE); //重复模式：RESTART---重新开始，REVERSE---恢复初始状态再开始
       mAnimator.start();
   }
   @Override
   protected void onAttachedToWindow() {
       super.onAttachedToWindow();
   }
   @Override
   protected void onDetachedFromWindow() {
       super.onDetachedFromWindow();
       mAnimator.end();  //关闭动画
   }
   @Override
   protected Parcelable onSaveInstanceState() {
       return super.onSaveInstanceState();
   }
   @Override
   protected void onRestoreInstanceState(Parcelable state) {
       super.onRestoreInstanceState(state);
   }
}

4、自定义view应用属性、刷新显示

Android里，一个view的绘制流程包括： Measure、Layout、Draw 测量&mdash;&mdash;onMeasure()：决定View的大小，确定view及它所有子节点需要的尺寸 布局&mdash;&mdash;onLayout()：决定View在ViewGroup中的位置, 当view需要为它的所有子节点指定大小和布局时，调用此方法 绘制&mdash;&mdash;onDraw()：绘制View。 自定义View中，onLayout配合onMeasure方法一起使用，可以实现自定义View的复杂布局。

自定义view，刷新view的方法： requestLayout()、invalidate()、postInvalidate()， 其实invalidate和postInvalidate这两个方法作用是一样的，唯一不同: invalidate用在主线程 postInvalidate用在异步线程，它最后会通过handler调用invalidate实现

requestLayout和invalidate的内部实现： requestLayout 会调用measure和layout 等一系列操作，然后根据布局是否发生改变，surface是否被销毁，来决定是否调用draw，也就是说requestlayout肯定会调用measure和layout， 但不一定调用draw，读者可以试着改下我上面写的那个小程序，将postInvalidate改成requestlayout，动画效果就消失了，因为布局没有发生改变。 invalidate 只会调用draw，而且肯定会调，即使什么都没有发生改变，它也会重新绘制。 所以如果有布局需要发生改变，需要调用requestlayout方法，如果只是刷新动画，则只需要调用invalidate方法

postInvalidate()方法程序调用流程，从View.java到ViewRootImpl.java，最终由performTraversals()实现 postInvalidate => postInvalidateDelayed => dispatchInvalidateDelayed => invalidate => scheduleTraversals() => doTraversal => performTraversals

requestLayout()方法程序调用流程 requestLayout() => scheduleTraversals() => doTraversal => performTraversals

performTraversals()方法调用：（真正实现view的measure、layout、draw） performMeasure(childWidthMeasureSpec, childHeightMeasureSpec); performMeasure() => measure() => onMeasure() 调用该方法来确定view及它所有子节点需要的尺寸 performLayout(lp, desiredWindowWidth, desiredWindowHeight); performLayout() => layout() => onLayout() 当view需要为它的所有子节点指定大小和布局时，调用此方法 performDraw(); performDraw() => draw() => onDraw() => dispatchDraw() (drawSoftware())

onMeasure(int widthMeasureSpec, int heightMeasureSpec) 功能：通过测量知道一个view要占的大小， 参数：宽高测量规格，int型的值（java中int型由4个字节（32bit）组成），在MeasureSpce中，其前两位表示mode，后30位表示size MeasureSpce的mode有三种：EXACTLY、AT_MOST、UNSPECIFIED

1、当父布局是EXACTLY时， 子控件确定大小或者match_parent，mode都是EXACTLY， 子控件是wrap_content时，mode为AT_MOST；

2、当父布局是AT_MOST时， 子控件确定大小，mode为EXACTLY， 子控件wrap_content或者match_parent时，mode为AT_MOST。 所以在确定控件大小时，需要判断MeasureSpec的mode，不能直接用MeasureSpec的size

View.java:

public class View implements Drawable.Callback, KeyEvent.Callback,
       AccessibilityEventSource {
   ...
   public void requestLayout() {
       if (mMeasureCache != null) mMeasureCache.clear();
       if (mAttachInfo != null && mAttachInfo.mViewRequestingLayout == null) {
           // Only trigger request-during-layout logic if this is the view requesting it,
           // not the views in its parent hierarchy
           ViewRootImpl viewRoot = getViewRootImpl();
           if (viewRoot != null && viewRoot.isInLayout()) {
               if (!viewRoot.requestLayoutDuringLayout(this)) {
                   return;
               }
           }
           mAttachInfo.mViewRequestingLayout = this;
       }
       mPrivateFlags |= PFLAG_FORCE_LAYOUT;
       mPrivateFlags |= PFLAG_INVALIDATED;
       if (mParent != null && !mParent.isLayoutRequested()) {
           mParent.requestLayout(); //ViewParent接口的requestLayout()方法
       }
       if (mAttachInfo != null && mAttachInfo.mViewRequestingLayout == this) {
           mAttachInfo.mViewRequestingLayout = null;
       }
   }
   public final void measure(int widthMeasureSpec, int heightMeasureSpec) { //为整个View树计算实际的大小, 需要递归的去计算每一个子视图的大小
       boolean optical = isLayoutModeOptical(this);
       if (optical != isLayoutModeOptical(mParent)) {
           Insets insets = getOpticalInsets();
           int oWidth  = insets.left + insets.right;
           int oHeight = insets.top  + insets.bottom;
           widthMeasureSpec  = MeasureSpec.adjust(widthMeasureSpec,  optical ? -oWidth  : oWidth);
           heightMeasureSpec = MeasureSpec.adjust(heightMeasureSpec, optical ? -oHeight : oHeight);
       }
       // Suppress sign extension for the low bytes
       long key = (long) widthMeasureSpec << 32 | (long) heightMeasureSpec & 0xffffffffL;
       if (mMeasureCache == null)
          mMeasureCache = new LongSparseLongArray(2);
       final boolean forceLayout = (mPrivateFlags & PFLAG_FORCE_LAYOUT) == PFLAG_FORCE_LAYOUT;
       final boolean isExactly   = MeasureSpec.getMode(widthMeasureSpec) == MeasureSpec.EXACTLY && MeasureSpec.getMode(heightMeasureSpec) == MeasureSpec.EXACTLY;
       final boolean matchingSize = isExactly &&
               getMeasuredWidth() == MeasureSpec.getSize(widthMeasureSpec) &&
               getMeasuredHeight() == MeasureSpec.getSize(heightMeasureSpec);
       if (forceLayout || !matchingSize && (widthMeasureSpec != mOldWidthMeasureSpec || heightMeasureSpec != mOldHeightMeasureSpec)) {
           // first clears the measured dimension flag
           mPrivateFlags &= ~PFLAG_MEASURED_DIMENSION_SET;
           resolveRtlPropertiesIfNeeded();
           int cacheIndex = forceLayout ? -1 : mMeasureCache.indexOfKey(key);
           if (cacheIndex < 0 || sIgnoreMeasureCache) {
               // measure ourselves, this should set the measured dimension flag back
               onMeasure(widthMeasureSpec, heightMeasureSpec);
               mPrivateFlags3 &= ~PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT;
           } else {
               long value = mMeasureCache.valueAt(cacheIndex);
               // Casting a long to int drops the high 32 bits, no mask needed
               setMeasuredDimensionRaw((int) (value >> 32), (int) value);
               mPrivateFlags3 |= PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT;
           }
           // flag not set, setMeasuredDimension() was not invoked, we raise
           // an exception to warn the developer
           if ((mPrivateFlags & PFLAG_MEASURED_DIMENSION_SET) != PFLAG_MEASURED_DIMENSION_SET) {
               throw new IllegalStateException("onMeasure() did not set the"
                       + " measured dimension by calling"
                       + " setMeasuredDimension()");
           }
           mPrivateFlags |= PFLAG_LAYOUT_REQUIRED;
       }
       mOldWidthMeasureSpec = widthMeasureSpec;
       mOldHeightMeasureSpec = heightMeasureSpec;
       mMeasureCache.put(key, ((long) mMeasuredWidth) << 32 | (long) mMeasuredHeight & 0xffffffffL); // suppress sign extension
   }
   //对于每个View的实际宽高都是由父视图和本身视图决定的
   protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { //计算出实际的高(mMeasuredHeight)和宽(mMeasureWidth)传入setMeasuredDimension()方法完成单个View的测量
       setMeasuredDimension(getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec),
               getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec));
   }
   protected final void setMeasuredDimension(int measuredWidth, int measuredHeight) {
       boolean optical = isLayoutModeOptical(this);
       if (optical != isLayoutModeOptical(mParent)) {
           Insets insets = getOpticalInsets();
           int opticalWidth  = insets.left + insets.right;
           int opticalHeight = insets.top  + insets.bottom;
           measuredWidth  += optical ? opticalWidth  : -opticalWidth;
           measuredHeight += optical ? opticalHeight : -opticalHeight;
       }
       setMeasuredDimensionRaw(measuredWidth, measuredHeight);
   }
   private void setMeasuredDimensionRaw(int measuredWidth, int measuredHeight) {
       mMeasuredWidth = measuredWidth;
       mMeasuredHeight = measuredHeight;
       mPrivateFlags |= PFLAG_MEASURED_DIMENSION_SET;
   }
   public void layout(int l, int t, int r, int b) { //为整个View树计算实际的位置, 需要递归的去计算每一个子视图的位置
       if ((mPrivateFlags3 & PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT) != 0) {
           onMeasure(mOldWidthMeasureSpec, mOldHeightMeasureSpec);
           mPrivateFlags3 &= ~PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT;
       }
       int oldL = mLeft;
       int oldT = mTop;
       int oldB = mBottom;
       int oldR = mRight;
       boolean changed = isLayoutModeOptical(mParent) ?  setOpticalFrame(l, t, r, b) : setFrame(l, t, r, b);
       if (changed || (mPrivateFlags & PFLAG_LAYOUT_REQUIRED) == PFLAG_LAYOUT_REQUIRED) {
           //调用onLayout回调方法，具体实现由重写了onLayout方法的ViewGroup的子类去实现
           onLayout(changed, l, t, r, b); //l，t，r，b四个值是子View相对于父View的值
           mPrivateFlags &= ~PFLAG_LAYOUT_REQUIRED;
           ListenerInfo li = mListenerInfo;
           if (li != null && li.mOnLayoutChangeListeners != null) {
               ArrayList<OnLayoutChangeListener> listenersCopy =
                       (ArrayList<OnLayoutChangeListener>)li.mOnLayoutChangeListeners.clone();
               int numListeners = listenersCopy.size();
               for (int i = 0; i < numListeners; ++i) {
                   listenersCopy.get(i).onLayoutChange(this, l, t, r, b, oldL, oldT, oldR, oldB);
               }
           }
       }
       mPrivateFlags &= ~PFLAG_FORCE_LAYOUT;
       mPrivateFlags3 |= PFLAG3_IS_LAID_OUT;
   }
   //onLayout被定义为抽象方法，继承ViewGroup时必须要重写该方法
   protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
   }
   public void draw(Canvas canvas) {
       final int privateFlags = mPrivateFlags;
       final boolean dirtyOpaque = (privateFlags & PFLAG_DIRTY_MASK) == PFLAG_DIRTY_OPAQUE &&
               (mAttachInfo == null || !mAttachInfo.mIgnoreDirtyState);
       mPrivateFlags = (privateFlags & ~PFLAG_DIRTY_MASK) | PFLAG_DRAWN;
       /*
        * Draw traversal performs several drawing steps which must be executed
        * in the appropriate order:
        *
        *      1. Draw the background
        *      2. If necessary, save the canvas' layers to prepare for fading
        *      3. Draw view's content
        *      4. Draw children
        *      5. If necessary, draw the fading edges and restore layers
        *      6. Draw decorations (scrollbars for instance)
        */
       // Step 1, draw the background, if needed
       int saveCount;
       if (!dirtyOpaque) {
           drawBackground(canvas);
       }
       // skip step 2 & 5 if possible (common case)
       final int viewFlags = mViewFlags;
       boolean horizontalEdges = (viewFlags & FADING_EDGE_HORIZONTAL) != 0;
       boolean verticalEdges = (viewFlags & FADING_EDGE_VERTICAL) != 0;
       if (!verticalEdges && !horizontalEdges) {
           // Step 3, draw the content
           if (!dirtyOpaque) onDraw(canvas);
           // Step 4, draw the children
           dispatchDraw(canvas);
           // Step 6, draw decorations (scrollbars)
           onDrawScrollBars(canvas);
           if (mOverlay != null && !mOverlay.isEmpty()) {
               mOverlay.getOverlayView().dispatchDraw(canvas);
           }
           // we're done...
           return;
       }
       ...
       // Step 3, draw the content
       if (!dirtyOpaque) onDraw(canvas);
       // Step 4, draw the children
       dispatchDraw(canvas);
       // Step 5, draw the fade effect and restore layers
       final Paint p = scrollabilityCache.paint;
       final Matrix matrix = scrollabilityCache.matrix;
       final Shader fade = scrollabilityCache.shader;
       if (drawTop) {
           matrix.setScale(1, fadeHeight * topFadeStrength);
           matrix.postTranslate(left, top);
           fade.setLocalMatrix(matrix);
           p.setShader(fade);
           canvas.drawRect(left, top, right, top + length, p);
       }
       if (drawBottom) {
           ...
       }
       if (drawLeft) {
           ...
       }
       if (drawRight) {
           ...
       }
       canvas.restoreToCount(saveCount);
       // Step 6, draw decorations (scrollbars)
       onDrawScrollBars(canvas);
       if (mOverlay != null && !mOverlay.isEmpty()) {
           mOverlay.getOverlayView().dispatchDraw(canvas); // 核心
       }
   }
   protected void dispatchDraw(Canvas canvas) {
   }
   public void postInvalidate() {
       postInvalidateDelayed(0);
   }
   public void postInvalidateDelayed(long delayMilliseconds) {
       // We try only with the AttachInfo because there's no point in invalidating
       // if we are not attached to our window
       final AttachInfo attachInfo = mAttachInfo;
       if (attachInfo != null) {
           attachInfo.mViewRootImpl.dispatchInvalidateDelayed(this, delayMilliseconds);
       }
   }
   ...
}  

ViewRootImpl.java

public final class ViewRootImpl implements ViewParent,
       View.AttachInfo.Callbacks, HardwareRenderer.HardwareDrawCallbacks {
   ...
   final class ViewRootHandler extends Handler {
       ...
       @Override
       public void handleMessage(Message msg) {
           switch (msg.what) {
           case MSG_INVALIDATE:
               ((View) msg.obj).invalidate();
               break;
           case MSG_INVALIDATE_RECT:
               final View.AttachInfo.InvalidateInfo info = (View.AttachInfo.InvalidateInfo) msg.obj;
               info.target.invalidate(info.left, info.top, info.right, info.bottom);
               info.recycle();
               break;
           case MSG_PROCESS_INPUT_EVENTS:
               mProcessInputEventsScheduled = false;
               doProcessInputEvents();
               break;
           case MSG_DISPATCH_APP_VISIBILITY:
               handleAppVisibility(msg.arg1 != 0);
               break;
           case MSG_DISPATCH_GET_NEW_SURFACE:
               handleGetNewSurface();
               break;
           case MSG_RESIZED: {
               // Recycled in the fall through...
               SomeArgs args = (SomeArgs) msg.obj;
               if (mWinFrame.equals(args.arg1)
                       && mPendingOverscanInsets.equals(args.arg5)
                       && mPendingContentInsets.equals(args.arg2)
                       && mPendingStableInsets.equals(args.arg6)
                       && mPendingVisibleInsets.equals(args.arg3)
                       && args.arg4 == null) {
                   break;
               }
               } // fall through...
           case MSG_RESIZED_REPORT:
               if (mAdded) {
                   ...
                   requestLayout();
               }
               break;
           case MSG_WINDOW_MOVED:
               if (mAdded) {
                   ...
                   requestLayout();
               }
               break;
           case MSG_WINDOW_FOCUS_CHANGED: {
               if (mAdded) {
                   boolean hasWindowFocus = msg.arg1 != 0;
                   mAttachInfo.mHasWindowFocus = hasWindowFocus;
                   profileRendering(hasWindowFocus);
                   if (hasWindowFocus) {
                       boolean inTouchMode = msg.arg2 != 0;
                       ensureTouchModeLocally(inTouchMode);
                       if (mAttachInfo.mHardwareRenderer != null && mSurface.isValid()){
                           mFullRedrawNeeded = true;
                           try {
                               final WindowManager.LayoutParams lp = mWindowAttributes;
                               final Rect surfaceInsets = lp != null ? lp.surfaceInsets : null;
                               mAttachInfo.mHardwareRenderer.initializeIfNeeded(
                                       mWidth, mHeight, mSurface, surfaceInsets);
                           } catch (OutOfResourcesException e) {
                               Log.e(TAG, "OutOfResourcesException locking surface", e);
                               try {
                                   if (!mWindowSession.outOfMemory(mWindow)) {
                                       Slog.w(TAG, "No processes killed for memory; killing self");
                                       Process.killProcess(Process.myPid());
                                   }
                               } catch (RemoteException ex) {
                               }
                               // Retry in a bit.
                               sendMessageDelayed(obtainMessage(msg.what, msg.arg1, msg.arg2), 500);
                               return;
                           }
                       }
                   }
                   mLastWasImTarget = WindowManager.LayoutParams
                           .mayUseInputMethod(mWindowAttributes.flags);
                   InputMethodManager imm = InputMethodManager.peekInstance();
                   if (mView != null) {
                       if (hasWindowFocus && imm != null && mLastWasImTarget &&
                               !isInLocalFocusMode()) {
                           imm.startGettingWindowFocus(mView);
                       }
                       mAttachInfo.mKeyDispatchState.reset();
                       mView.dispatchWindowFocusChanged(hasWindowFocus);
                       mAttachInfo.mTreeObserver.dispatchOnWindowFocusChange(hasWindowFocus);
                   }
                   // Note: must be done after the focus change callbacks,
                   // so all of the view state is set up correctly.
                   if (hasWindowFocus) {
                       if (imm != null && mLastWasImTarget && !isInLocalFocusMode()) {
                           imm.onWindowFocus(mView, mView.findFocus(),
                                   mWindowAttributes.softInputMode,
                                   !mHasHadWindowFocus, mWindowAttributes.flags);
                       }
                       // Clear the forward bit.  We can just do this directly, since
                       // the window manager doesn't care about it.
                       mWindowAttributes.softInputMode &=
                               ~WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION;
                       ((WindowManager.LayoutParams)mView.getLayoutParams())
                               .softInputMode &=
                                   ~WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION;
                       mHasHadWindowFocus = true;
                   }
                   if (mView != null && mAccessibilityManager.isEnabled()) {
                       if (hasWindowFocus) {
                           mView.sendAccessibilityEvent(
                                   AccessibilityEvent.TYPE_WINDOW_STATE_CHANGED);
                       }
                   }
               }
           } break;
           ...
           }
       }
   }
   final ViewRootHandler mHandler = new ViewRootHandler();
   public void dispatchInvalidateDelayed(View view, long delayMilliseconds) {
       Message msg = mHandler.obtainMessage(MSG_INVALIDATE, view);
       mHandler.sendMessageDelayed(msg, delayMilliseconds);
   }
   @Override
   public void requestLayout() {
       if (!mHandlingLayoutInLayoutRequest) {
           checkThread();
           mLayoutRequested = true; //
           scheduleTraversals(); // mTraversalRunnable => doTraversal => performTraversals
       }
   }
   @Override
   public boolean isLayoutRequested() {
       return mLayoutRequested;
   }
   void invalidate() {
       mDirty.set(0, 0, mWidth, mHeight);
       if (!mWillDrawSoon) {
           scheduleTraversals(); // mTraversalRunnable => doTraversal => performTraversals
       }
   }
   final class TraversalRunnable implements Runnable {
       @Override
       public void run() {
           doTraversal();
       }
   }
   final TraversalRunnable mTraversalRunnable = new TraversalRunnable();  
   void scheduleTraversals() {
       if (!mTraversalScheduled) {
           mTraversalScheduled = true;
           mTraversalBarrier = mHandler.getLooper().postSyncBarrier();
           mChoreographer.postCallback(
                   Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);
           if (!mUnbufferedInputDispatch) {
               scheduleConsumeBatchedInput();
           }
           notifyRendererOfFramePending();
       }
   }
   void unscheduleTraversals() {
       if (mTraversalScheduled) {
           mTraversalScheduled = false;
           mHandler.getLooper().removeSyncBarrier(mTraversalBarrier);
           mChoreographer.removeCallbacks(
                   Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);
       }
   }
   void doTraversal() {
       if (mTraversalScheduled) {
           mTraversalScheduled = false;
           mHandler.getLooper().removeSyncBarrier(mTraversalBarrier);
           if (mProfile) {
               Debug.startMethodTracing("ViewAncestor");
           }
           Trace.traceBegin(Trace.TRACE_TAG_VIEW, "performTraversals");
           try {
               performTraversals();
           } finally {
               Trace.traceEnd(Trace.TRACE_TAG_VIEW);
           }
           if (mProfile) {
               Debug.stopMethodTracing();
               mProfile = false;
           }
       }
   }
   private void performMeasure(int childWidthMeasureSpec, int childHeightMeasureSpec) {
       Trace.traceBegin(Trace.TRACE_TAG_VIEW, "measure");
       try {
           mView.measure(childWidthMeasureSpec, childHeightMeasureSpec); // 调用用View.java的measure()方法
       } finally {
           Trace.traceEnd(Trace.TRACE_TAG_VIEW);
       }
   }
   private void performLayout(WindowManager.LayoutParams lp, int desiredWindowWidth,
           int desiredWindowHeight) {
       mLayoutRequested = false;
       mScrollMayChange = true;
       mInLayout = true;
       final View host = mView;
       if (DEBUG_ORIENTATION || DEBUG_LAYOUT) {
           Log.v(TAG, "Laying out " + host + " to (" +
                   host.getMeasuredWidth() + ", " + host.getMeasuredHeight() + ")");
       }
       Trace.traceBegin(Trace.TRACE_TAG_VIEW, "layout");
       try {
           host.layout(0, 0, host.getMeasuredWidth(), host.getMeasuredHeight()); // 调用用View.java的layout()方法
           mInLayout = false;
           int numViewsRequestingLayout = mLayoutRequesters.size();
           if (numViewsRequestingLayout > 0) {
               // requestLayout() was called during layout.
               // If no layout-request flags are set on the requesting views, there is no problem.
               // If some requests are still pending, then we need to clear those flags and do
               // a full request/measure/layout pass to handle this situation.
               ArrayList<View> validLayoutRequesters = getValidLayoutRequesters(mLayoutRequesters,
                       false);
               if (validLayoutRequesters != null) {
                   // Set this flag to indicate that any further requests are happening during
                   // the second pass, which may result in posting those requests to the next
                   // frame instead
                   mHandlingLayoutInLayoutRequest = true;
                   // Process fresh layout requests, then measure and layout
                   int numValidRequests = validLayoutRequesters.size();
                   for (int i = 0; i < numValidRequests; ++i) {
                       final View view = validLayoutRequesters.get(i);
                       Log.w("View", "requestLayout() improperly called by " + view +
                               " during layout: running second layout pass");
                       view.requestLayout();
                   }
                   measureHierarchy(host, lp, mView.getContext().getResources(), desiredWindowWidth, desiredWindowHeight);
                   mInLayout = true;
                   host.layout(0, 0, host.getMeasuredWidth(), host.getMeasuredHeight());
                   mHandlingLayoutInLayoutRequest = false;
                   // Check the valid requests again, this time without checking/clearing the
                   // layout flags, since requests happening during the second pass get noop'd
                   validLayoutRequesters = getValidLayoutRequesters(mLayoutRequesters, true);
                   if (validLayoutRequesters != null) {
                       final ArrayList<View> finalRequesters = validLayoutRequesters;
                       // Post second-pass requests to the next frame
                       getRunQueue().post(new Runnable() {
                           @Override
                           public void run() {
                               int numValidRequests = finalRequesters.size();
                               for (int i = 0; i < numValidRequests; ++i) {
                                   final View view = finalRequesters.get(i);
                                   Log.w("View", "requestLayout() improperly called by " + view +
                                           " during second layout pass: posting in next frame");
                                   view.requestLayout();
                               }
                           }
                       });
                   }
               }
           }
       } finally {
           Trace.traceEnd(Trace.TRACE_TAG_VIEW);
       }
       mInLayout = false;
   }
   //performDraw() => draw() => drawSoftware()
   private void performDraw() {
       if (mAttachInfo.mDisplayState == Display.STATE_OFF && !mReportNextDraw) {
           return;
       }
       final boolean fullRedrawNeeded = mFullRedrawNeeded;
       mFullRedrawNeeded = false;
       mIsDrawing = true;
       Trace.traceBegin(Trace.TRACE_TAG_VIEW, "draw");
       try {
           draw(fullRedrawNeeded);
           // draw()调用 drawSoftware(surface, mAttachInfo, xOffset, yOffset, scalingRequired, dirty)
           // private boolean drawSoftware(Surface surface, AttachInfo attachInfo, int xoff, int yoff, boolean scalingRequired, Rect dirty)
       } finally {
           mIsDrawing = false;
           Trace.traceEnd(Trace.TRACE_TAG_VIEW);
       }
       // For whatever reason we didn't create a HardwareRenderer, end any
       // hardware animations that are now dangling
       if (mAttachInfo.mPendingAnimatingRenderNodes != null) {
           final int count = mAttachInfo.mPendingAnimatingRenderNodes.size();
           for (int i = 0; i < count; i++) {
               mAttachInfo.mPendingAnimatingRenderNodes.get(i).endAllAnimators();
           }
           mAttachInfo.mPendingAnimatingRenderNodes.clear();
       }
       if (mReportNextDraw) {
           mReportNextDraw = false;
           if (mAttachInfo.mHardwareRenderer != null) {
               mAttachInfo.mHardwareRenderer.fence();
           }
           if (LOCAL_LOGV) {
               Log.v(TAG, "FINISHED DRAWING: " + mWindowAttributes.getTitle());
           }
           if (mSurfaceHolder != null && mSurface.isValid()) {
               mSurfaceHolderCallback.surfaceRedrawNeeded(mSurfaceHolder);
               SurfaceHolder.Callback callbacks[] = mSurfaceHolder.getCallbacks();
               if (callbacks != null) {
                   for (SurfaceHolder.Callback c : callbacks) {
                       if (c instanceof SurfaceHolder.Callback2) {
                           ((SurfaceHolder.Callback2)c).surfaceRedrawNeeded(
                                   mSurfaceHolder);
                       }
                   }
               }
           }
           try {
               mWindowSession.finishDrawing(mWindow);
           } catch (RemoteException e) {
           }
       }
   }
   ...
}

来源：https://blog.csdn.net/keen_zuxwang/article/details/74456018