android应用程序窗口框架学习（1）-view绘制流程源代码解析

博客原来的地址是：http://blog.csdn.net/xyz_lmn/article/details/20385049

Android的View绘制是从根节点（Activity是DecorView）开始，他是一个自上而下的过程。View的绘制经历三个过程：Measure、Layout、Draw。基本流程如下图：



performTraversals函数，具体的可以参考一下源代码：

[java] view
plaincopyprint?





private void performTraversals() {

final View host = mView;

...

host.measure(childWidthMeasureSpec, childHeightMeasureSpec);

...

host.layout(0, 0, host.getMeasuredWidth(), host.getMeasuredHeight());

...

draw(fullRedrawNeeded);

}

1、Measure过程

Measure过程是计算视图大小，View中视图measure过程相关的方法主要有三个：

[java] view
plaincopyprint?





public final void measure(int widthMeasureSpec, int heightMeasureSpec)

protected final void setMeasuredDimension(int measuredWidth, int measuredHeight)

protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec)

measure调用onMeasure，onMeasure调用setMeasureDimension，measure，setMeasureDimension是final类型，view的子类不需要重写，onMeasure在view的子类中重写。

measure函数：

[java] view
plaincopyprint?





public final void measure(int widthMeasureSpec, int heightMeasureSpec) {

if ((mPrivateFlags & FORCE_LAYOUT) == FORCE_LAYOUT ||

widthMeasureSpec != mOldWidthMeasureSpec ||

heightMeasureSpec != mOldHeightMeasureSpec) {

// first clears the measured dimension flag

mPrivateFlags &= ~MEASURED_DIMENSION_SET;

if (ViewDebug.TRACE_HIERARCHY) {

ViewDebug.trace(this, ViewDebug.HierarchyTraceType.ON_MEASURE);

}

// measure ourselves, this should set the measured dimension flag back

onMeasure(widthMeasureSpec, heightMeasureSpec);

// flag not set, setMeasuredDimension() was not invoked, we raise

// an exception to warn the developer

if ((mPrivateFlags & MEASURED_DIMENSION_SET) != MEASURED_DIMENSION_SET) {

throw new IllegalStateException("onMeasure() did not set the"

+ " measured dimension by calling"

+ " setMeasuredDimension()");

}

mPrivateFlags |= LAYOUT_REQUIRED;

}

mOldWidthMeasureSpec = widthMeasureSpec;

mOldHeightMeasureSpec = heightMeasureSpec;

}

onMeasure函数：

[java] view
plaincopyprint?





protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {

setMeasuredDimension(getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec),

getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec));

}

重写onMeasure时，要调用setMeasuredDimension或者super.onMeasure来设置自身的mMeasuredWidth和mMeasuredHeight，否则，就会抛出异常.

setMeasuredDimension函数，用来设置view的大小：

[java] view
plaincopyprint?





protected final void setMeasuredDimension(int measuredWidth, int measuredHeight) {

mMeasuredWidth = measuredWidth;

mMeasuredHeight = measuredHeight;

mPrivateFlags |= MEASURED_DIMENSION_SET;

}

再看一下onMeasure的getDefaultSize函数：

[java] view
plaincopyprint?





public static int getDefaultSize(int size, int measureSpec) {

int result = size;

int specMode = MeasureSpec.getMode(measureSpec);

int specSize = MeasureSpec.getSize(measureSpec);

switch (specMode) {

case MeasureSpec.UNSPECIFIED:

result = size;

break;

case MeasureSpec.AT_MOST:

case MeasureSpec.EXACTLY:

result = specSize;

break;

}

return result;

}

这里用引入了MeasureSpec类：

[java] view
plaincopyprint?





public static class MeasureSpec {

private static final int MODE_SHIFT = 30;

private static final int MODE_MASK = 0x3 << MODE_SHIFT;

public static final int UNSPECIFIED = 0 << MODE_SHIFT;

public static final int EXACTLY = 1 << MODE_SHIFT;

public static final int AT_MOST = 2 << MODE_SHIFT;

public static int makeMeasureSpec(int size, int mode) {

return size + mode;

}

public static int getMode(int measureSpec) {

return (measureSpec & MODE_MASK);

}

public static int getSize(int measureSpec) {

return (measureSpec & ~MODE_MASK);

}

}

MODE_MASK为30为长度的二进制数，前两位标示Mode，后面的标示Size。MeasureSpec有三种模式分别是UNSPECIFIED, EXACTLY和AT_MOST。

EXACTLY表示父视图希望子视图的大小应该是由specSize的值来决定的，系统默认会按照这个规则来设置子视图的大小，开发人员当然也可以按照自己的意愿设置成任意的大小。

AT_MOST表示子视图最多只能是specSize中指定的大小，开发人员应该尽可能小得去设置这个视图，并且保证不会超过specSize。系统默认会按照这个规则来设置子视图的大小，开发人员当然也可以按照自己的意愿设置成任意的大小。

UNSPECIFIED表示开发人员可以将视图按照自己的意愿设置成任意的大小，没有任何限制。这种情况比较少见，不太会用到。

widthMeasureSpec和heightMeasureSpec决定了Mode和Size的值，widthMeasureSpec和heightMeasureSpec来自父视图，这两个值都是由父视图经过计算后传递给子视图的，说明父视图会在一定程度上决定子视图的大小。但是最外层的根视图，它的widthMeasureSpec和heightMeasureSpec又是从哪里得到的呢？这就需要去分析ViewRoot中的源码了，观察performTraversals()方法可以发现如下代码：

[java] view
plaincopyprint?





childWidthMeasureSpec = getRootMeasureSpec(desiredWindowWidth, lp.width);

childHeightMeasureSpec = getRootMeasureSpec(desiredWindowHeight, lp.height);

可以看到，这里调用了getRootMeasureSpec()方法去获取widthMeasureSpec和heightMeasureSpec的值，注意方法中传入的参数，其中lp.width和lp.height在创建ViewGroup实例的时候就被赋值了，它们都等于MATCH_PARENT。然后看下getRootMeasureSpec()方法中的代码，如下所示：

[java] view
plaincopyprint?





private int getRootMeasureSpec(int windowSize, int rootDimension) {

int measureSpec;

switch (rootDimension) {

case ViewGroup.LayoutParams.MATCH_PARENT:

measureSpec = MeasureSpec.makeMeasureSpec(windowSize, MeasureSpec.EXACTLY);

break;

case ViewGroup.LayoutParams.WRAP_CONTENT:

measureSpec = MeasureSpec.makeMeasureSpec(windowSize, MeasureSpec.AT_MOST);

break;

default:

measureSpec = MeasureSpec.makeMeasureSpec(rootDimension, MeasureSpec.EXACTLY);

break;

}

return measureSpec;

}

可以看到，这里使用了MeasureSpec.makeMeasureSpec()方法来组装一个MeasureSpec，当rootDimension参数等于MATCH_PARENT的时候，MeasureSpec的specMode就等于EXACTLY，当rootDimension等于WRAP_CONTENT的时候，MeasureSpec的specMode就等于AT_MOST。并且MATCH_PARENT和WRAP_CONTENT时的specSize都是等于windowSize的，也就意味着根视图总是会充满全屏的。

Measure是一个复杂的过程，因为一个布局中一般都会包含多个子视图，每个视图都需要经历一次measure过程。ViewGroup中定义了一个measureChildren()方法来去测量子视图的大小，如下所示：

[java] view
plaincopyprint?





protected void measureChildren(int widthMeasureSpec, int heightMeasureSpec) {

final int size = mChildrenCount;

final View[] children = mChildren;

for (int i = 0; i < size; ++i) {

final View child = children[i];

if ((child.mViewFlags & VISIBILITY_MASK) != GONE) {

measureChild(child, widthMeasureSpec, heightMeasureSpec);

}

}

}

这里会去遍历当前布局下的所有子视图，然后逐个调用measureChild()方法来测量相应子视图的大小：

[java] view
plaincopyprint?





protected void measureChild(View child, int parentWidthMeasureSpec,

int parentHeightMeasureSpec) {

final LayoutParams lp = child.getLayoutParams();

final int childWidthMeasureSpec = getChildMeasureSpec(parentWidthMeasureSpec,

mPaddingLeft + mPaddingRight, lp.width);

final int childHeightMeasureSpec = getChildMeasureSpec(parentHeightMeasureSpec,

mPaddingTop + mPaddingBottom, lp.height);

child.measure(childWidthMeasureSpec, childHeightMeasureSpec);

}

从这里我们可以看到视图的大小是由父视图和子视图共同决定的。子布局里面的android:layout_width和android:layout_height只是期望值，父View大小最终是由DecorView决定。父视图提供尺寸大小的一个能力，子视图最终尺寸与父视图能力、子视图期望的关系如下：

父视图能力尺寸	子视图期望尺寸	子视图最终允许尺寸
EXACTLY + Size1	EXACTLY + Size2	EXACTLY + Size2
EXACTLY + Size1	fill_parent/match_parent	EXACTLY+Size1
EXACTLY + Size1	wrap_content	AT_MOST+Size1
AT_MOST+Size1	EXACTLY + Size2	EXACTLY+Size2
AT_MOST+Size1	fill_parent/match_parent	AT_MOST+Size1
AT_MOST+Size1	wrap_content	AT_MOST+Size1
UNSPECIFIED+Size1	EXACTLY + Size2	EXACTLY + Size2
UNSPECIFIED+Size1	fill_parent/match_parent	UNSPECIFIED+0
UNSPECIFIED+Size1	wrap_content	UNSPECIFIED+0

关于视图的measure过程可以阅读以下LinearLayout源码，这样可以更清楚的了解过程。

2、Layout过程

measure过程确定视图的大小，而layout过程确定视图的位置。loyout是从view的layout方法开始的：

[java] view
plaincopyprint?





public void layout(int l, int t, int r, int b) {

int oldL = mLeft;

int oldT = mTop;

int oldB = mBottom;

int oldR = mRight;

boolean changed = setFrame(l, t, r, b);

if (changed || (mPrivateFlags & PFLAG_LAYOUT_REQUIRED) == PFLAG_LAYOUT_REQUIRED) {

onLayout(changed, l, t, r, b);

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;

}

函数中参数l、t、r、b是指view的左、上、右、底的位置，这几个参数是父视图传入的，而根视图中参数是由performTraversals()方法传入的。

[java] view
plaincopyprint?





host.layout(0, 0, host.mMeasuredWidth, host.mMeasuredHeight);

layout中调用了onLayout方法，在view中onLayout方法是一个空函数，他需要其子类实现。

[java] view
plaincopyprint?





protected void onLayout(boolean changed, int left, int top, int right, int bottom) {

}

我们关注一下LinearLayout：

[java] view
plaincopyprint?





@Override

protected void onLayout(boolean changed, int l, int t, int r, int b) {

if (mOrientation == VERTICAL) {

layoutVertical();

} else {

layoutHorizontal();

}

}

[java] view
plaincopyprint?





void layoutVertical() {

final int paddingLeft = mPaddingLeft;

int childTop;

int childLeft;

// Where right end of child should go

final int width = mRight - mLeft;

int childRight = width - mPaddingRight;

// Space available for child

int childSpace = width - paddingLeft - mPaddingRight;

final int count = getVirtualChildCount();

final int majorGravity = mGravity & Gravity.VERTICAL_GRAVITY_MASK;

final int minorGravity = mGravity & Gravity.RELATIVE_HORIZONTAL_GRAVITY_MASK;

switch (majorGravity) {

case Gravity.BOTTOM:

// mTotalLength contains the padding already

childTop = mPaddingTop + mBottom - mTop - mTotalLength;

break;

// mTotalLength contains the padding already

case Gravity.CENTER_VERTICAL:

childTop = mPaddingTop + (mBottom - mTop - mTotalLength) / 2;

break;

case Gravity.TOP:

default:

childTop = mPaddingTop;

break;

}

for (int i = 0; i < count; i++) {

final View child = getVirtualChildAt(i);

if (child == null) {

childTop += measureNullChild(i);

} else if (child.getVisibility() != GONE) {

final int childWidth = child.getMeasuredWidth();

final int childHeight = child.getMeasuredHeight();

final LinearLayout.LayoutParams lp =

(LinearLayout.LayoutParams) child.getLayoutParams();

int gravity = lp.gravity;

if (gravity < 0) {

gravity = minorGravity;

}

final int layoutDirection = getLayoutDirection();

final int absoluteGravity = Gravity.getAbsoluteGravity(gravity, layoutDirection);

switch (absoluteGravity & Gravity.HORIZONTAL_GRAVITY_MASK) {

case Gravity.CENTER_HORIZONTAL:

childLeft = paddingLeft + ((childSpace - childWidth) / 2)

+ lp.leftMargin - lp.rightMargin;

break;

case Gravity.RIGHT:

childLeft = childRight - childWidth - lp.rightMargin;

break;

case Gravity.LEFT:

default:

childLeft = paddingLeft + lp.leftMargin;

break;

}

if (hasDividerBeforeChildAt(i)) {

childTop += mDividerHeight;

}

childTop += lp.topMargin;

setChildFrame(child, childLeft, childTop + getLocationOffset(child),

childWidth, childHeight);

childTop += childHeight + lp.bottomMargin + getNextLocationOffset(child);

i += getChildrenSkipCount(child, i);

}

}

}

layout设置了view的位置，还设置了子视图位置，layoutHorizontal()方法中调用了setChildFrame方法：

[java] view
plaincopyprint?





private void setChildFrame(View child, int left, int top, int width, int height) {

child.layout(left, top, left + width, top + height);

}

从上面看出，layout也是一个自上而下的过程，先设置父视图位置，在循环子视图，父视图位置一定程度上决定了子视图位置。

3、Draw过程

draw过程调用顺序在measure()和layout()之后，同样的，performTraversals()发起的draw过程最终会调用到mView的draw()函数，这里的mView对于Activity来说就是PhoneWindow.DecorView。看一下view类的draw方法：

[java] view
plaincopyprint?





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) {

final Drawable background = mBackground;

if (background != null) {

final int scrollX = mScrollX;

final int scrollY = mScrollY;

if (mBackgroundSizeChanged) {

background.setBounds(0, 0, mRight - mLeft, mBottom - mTop);

mBackgroundSizeChanged = false;

}

if ((scrollX | scrollY) == 0) {

background.draw(canvas);

} else {

canvas.translate(scrollX, scrollY);

background.draw(canvas);

canvas.translate(-scrollX, -scrollY);

}

}

}

// 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);

// we're done...

return;

}

/*

* Here we do the full fledged routine...

* (this is an uncommon case where speed matters less,

* this is why we repeat some of the tests that have been

* done above)

*/

boolean drawTop = false;

boolean drawBottom = false;

boolean drawLeft = false;

boolean drawRight = false;

float topFadeStrength = 0.0f;

float bottomFadeStrength = 0.0f;

float leftFadeStrength = 0.0f;

float rightFadeStrength = 0.0f;

// Step 2, save the canvas' layers

int paddingLeft = mPaddingLeft;

final boolean offsetRequired = isPaddingOffsetRequired();

if (offsetRequired) {

paddingLeft += getLeftPaddingOffset();

}

int left = mScrollX + paddingLeft;

int right = left + mRight - mLeft - mPaddingRight - paddingLeft;

int top = mScrollY + getFadeTop(offsetRequired);

int bottom = top + getFadeHeight(offsetRequired);

if (offsetRequired) {

right += getRightPaddingOffset();

bottom += getBottomPaddingOffset();

}

final ScrollabilityCache scrollabilityCache = mScrollCache;

final float fadeHeight = scrollabilityCache.fadingEdgeLength;

int length = (int) fadeHeight;

// clip the fade length if top and bottom fades overlap

// overlapping fades produce odd-looking artifacts

if (verticalEdges && (top + length > bottom - length)) {

length = (bottom - top) / 2;

}

// also clip horizontal fades if necessary

if (horizontalEdges && (left + length > right - length)) {

length = (right - left) / 2;

}

if (verticalEdges) {

topFadeStrength = Math.max(0.0f, Math.min(1.0f, getTopFadingEdgeStrength()));

drawTop = topFadeStrength * fadeHeight > 1.0f;

bottomFadeStrength = Math.max(0.0f, Math.min(1.0f, getBottomFadingEdgeStrength()));

drawBottom = bottomFadeStrength * fadeHeight > 1.0f;

}

if (horizontalEdges) {

leftFadeStrength = Math.max(0.0f, Math.min(1.0f, getLeftFadingEdgeStrength()));

drawLeft = leftFadeStrength * fadeHeight > 1.0f;

rightFadeStrength = Math.max(0.0f, Math.min(1.0f, getRightFadingEdgeStrength()));

drawRight = rightFadeStrength * fadeHeight > 1.0f;

}

saveCount = canvas.getSaveCount();

int solidColor = getSolidColor();

if (solidColor == 0) {

final int flags = Canvas.HAS_ALPHA_LAYER_SAVE_FLAG;

if (drawTop) {

canvas.saveLayer(left, top, right, top + length, null, flags);

}

if (drawBottom) {

canvas.saveLayer(left, bottom - length, right, bottom, null, flags);

}

if (drawLeft) {

canvas.saveLayer(left, top, left + length, bottom, null, flags);

}

if (drawRight) {

canvas.saveLayer(right - length, top, right, bottom, null, flags);

}

} else {

scrollabilityCache.setFadeColor(solidColor);

}

// 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);

canvas.drawRect(left, top, right, top + length, p);

}

if (drawBottom) {

matrix.setScale(1, fadeHeight * bottomFadeStrength);

matrix.postRotate(180);

matrix.postTranslate(left, bottom);

fade.setLocalMatrix(matrix);

canvas.drawRect(left, bottom - length, right, bottom, p);

}

if (drawLeft) {

matrix.setScale(1, fadeHeight * leftFadeStrength);

matrix.postRotate(-90);

matrix.postTranslate(left, top);

fade.setLocalMatrix(matrix);

canvas.drawRect(left, top, left + length, bottom, p);

}

if (drawRight) {

matrix.setScale(1, fadeHeight * rightFadeStrength);

matrix.postRotate(90);

matrix.postTranslate(right, top);

fade.setLocalMatrix(matrix);

canvas.drawRect(right - length, top, right, bottom, p);

}

canvas.restoreToCount(saveCount);

// Step 6, draw decorations (scrollbars)

onDrawScrollBars(canvas);

}

draw方法分成了6个步骤：

[html] view
plaincopyprint?





/*

* 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)

*/

第三部, Draw view's content步骤调用了onDraw方法，子类中实现onDraw方法。

第四步，Draw children步骤使用的dispatchDraw方法，这个方法在ViewGroup中有实现。

View或ViewGroup的子类不用再重载ViewGroup中该方法，因为它已经有了默认而且标准的view系统流程。dispatchDraw()内部for循环调用drawChild()分别绘制每一个子视图，而drawChild()内部又会调用draw（）函数完成子视图的内部绘制工作。

[java] view
plaincopyprint?





/**

* {@inheritDoc}

*/

@Override

protected void dispatchDraw(Canvas canvas) {

final int count = mChildrenCount;

final View[] children = mChildren;

int flags = mGroupFlags;

if ((flags & FLAG_RUN_ANIMATION) != 0 && canAnimate()) {

final boolean cache = (mGroupFlags & FLAG_ANIMATION_CACHE) == FLAG_ANIMATION_CACHE;

final boolean buildCache = !isHardwareAccelerated();

for (int i = 0; i < count; i++) {

final View child = children[i];

if ((child.mViewFlags & VISIBILITY_MASK) == VISIBLE) {

final LayoutParams params = child.getLayoutParams();

attachLayoutAnimationParameters(child, params, i, count);

bindLayoutAnimation(child);

if (cache) {

child.setDrawingCacheEnabled(true);

if (buildCache) {

child.buildDrawingCache(true);

}

}

}

}

final LayoutAnimationController controller = mLayoutAnimationController;

if (controller.willOverlap()) {

mGroupFlags |= FLAG_OPTIMIZE_INVALIDATE;

}

controller.start();

mGroupFlags &= ~FLAG_RUN_ANIMATION;

mGroupFlags &= ~FLAG_ANIMATION_DONE;

if (cache) {

mGroupFlags |= FLAG_CHILDREN_DRAWN_WITH_CACHE;

}

if (mAnimationListener != null) {

mAnimationListener.onAnimationStart(controller.getAnimation());

}

}

int saveCount = 0;

final boolean clipToPadding = (flags & CLIP_TO_PADDING_MASK) == CLIP_TO_PADDING_MASK;

if (clipToPadding) {

saveCount = canvas.save();

canvas.clipRect(mScrollX + mPaddingLeft, mScrollY + mPaddingTop,

mScrollX + mRight - mLeft - mPaddingRight,

mScrollY + mBottom - mTop - mPaddingBottom);

}

// We will draw our child's animation, let's reset the flag

mPrivateFlags &= ~PFLAG_DRAW_ANIMATION;

mGroupFlags &= ~FLAG_INVALIDATE_REQUIRED;

boolean more = false;

final long drawingTime = getDrawingTime();

if ((flags & FLAG_USE_CHILD_DRAWING_ORDER) == 0) {

for (int i = 0; i < count; i++) {

final View child = children[i];

if ((child.mViewFlags & VISIBILITY_MASK) == VISIBLE || child.getAnimation() != null) {

more |= drawChild(canvas, child, drawingTime);

}

}

} else {

for (int i = 0; i < count; i++) {

final View child = children[getChildDrawingOrder(count, i)];

if ((child.mViewFlags & VISIBILITY_MASK) == VISIBLE || child.getAnimation() != null) {

more |= drawChild(canvas, child, drawingTime);

}

}

}

// Draw any disappearing views that have animations

if (mDisappearingChildren != null) {

final ArrayList<View> disappearingChildren = mDisappearingChildren;

final int disappearingCount = disappearingChildren.size() - 1;

// Go backwards -- we may delete as animations finish

for (int i = disappearingCount; i >= 0; i--) {

final View child = disappearingChildren.get(i);

more |= drawChild(canvas, child, drawingTime);

}

}

if (debugDraw()) {

onDebugDraw(canvas);

}

if (clipToPadding) {

canvas.restoreToCount(saveCount);

}

// mGroupFlags might have been updated by drawChild()

flags = mGroupFlags;

if ((flags & FLAG_INVALIDATE_REQUIRED) == FLAG_INVALIDATE_REQUIRED) {

invalidate(true);

}

if ((flags & FLAG_ANIMATION_DONE) == 0 && (flags & FLAG_NOTIFY_ANIMATION_LISTENER) == 0 &&

mLayoutAnimationController.isDone() && !more) {

// We want to erase the drawing cache and notify the listener after the

// next frame is drawn because one extra invalidate() is caused by

// drawChild() after the animation is over

mGroupFlags |= FLAG_NOTIFY_ANIMATION_LISTENER;

final Runnable end = new Runnable() {

public void run() {

notifyAnimationListener();

}

};

post(end);

}

}

上面基本介绍完了View的绘制流程。更多的细节需要在日常学习中总结。