9.view 作图过程,讲讲draw/onDraw和drawChild

 public final void measure (int widthMeasureSpec, int heightMeasureSpec) {....// measure ourselves, this should set the measured dimension flag backonMeasure(widthMeasureSpec, heightMeasureSpec);....    mOldWidthMeasureSpec = widthMeasureSpec;mOldHeightMeasureSpec = heightMeasureSpec;}

  protected void onMeasure( int widthMeasureSpec, int heightMeasureSpec) {setMeasuredDimensiongetDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec),getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec));}

  protected int getSuggestedMinimumWidth() {int suggestedMinWidth = mMinWidth ;if (mBGDrawable != null) {final int bgMinWidth = mBGDrawable.getMinimumWidth();if (suggestedMinWidth < bgMinWidth) {suggestedMinWidth = bgMinWidth;}}return suggestedMinWidth</strong>;//返回背景图最小值和view最小值中的较大者}

  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;//UNSPECIFIED，返回值为size值break;case MeasureSpec.AT_MOST://AT_MOST，返回值为size值case MeasureSpec.EXACTLY:result = specSize;//EXACTLY，返回值为specSize值break;}return result;}

 protected final void setMeasuredDimension (int measuredWidth, int measuredHeight) {mMeasuredWidth = measuredWidth;mMeasuredHeight = measuredHeight;mPrivateFlags |= MEASURED_DIMENSION_SET ;}

  /*** Ask all of the children of this view to measure themselves, taking into account both the MeasureSpec requirements for this view and its padding.* We skip children that are in the GONE state The heavy lifting is done in getChildMeasureSpec.     * @param widthMeasureSpec The width requirements for this view* @param heightMeasureSpec The height requirements for this view*/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) {//过滤掉GONE的viewmeasureChild(child, widthMeasureSpec, heightMeasureSpec);//让所有的子view measure自己。调用measureChild方法。}}}

  /*** Ask one of the children of this view to measure itself, taking into account both the MeasureSpec requirements for this view and its padding.* The heavy lifting is done in getChildMeasureSpec.* @param child The child to measure* @param parentWidthMeasureSpec The width requirements for this view* @param parentHeightMeasureSpec The height requirements for this view*/protected void measureChild(View child, int parentWidthMeasureSpec,int parentHeightMeasureSpec) {final LayoutParams lp = child.getLayoutParams();//主要工作还是在getChildMeasureSpec函数中进行final int childWidthMeasureSpec = getChildMeasureSpec</strong>(parentWidthMeasureSpec,mPaddingLeft+mPaddingRight, lp.width);final int childHeightMeasureSpec = getChildMeasureSpec</strong>(parentHeightMeasureSpec, mPaddingTop+ mPaddingBottom, lp.height);child.measure</strong>(childWidthMeasureSpchildHeightMeasureSpec ec, childHeightMeasureSpec);//计算完childWidthMeasureSpec 、childHeightMeasureSpec 调用子view的measure方法}

  / * Does the hard part of measureChildren: figuring out the MeasureSpec to pass to a particular child. This method figures out the right MeasureSpec for one dimension (height or width) of one child view. The goal is to combine information from ourMeasureSpec with the LayoutParams of the child to get the best possible results. For example,if the this view knows its size (because its MeasureSpec has a mode of EXACTLY), and the child has indicated in its LayoutParamsthat it wants to be the same size as the parent, the parent should ask the child to layout given an exact size.* @param spec The requirements for this view* @param padding The padding of this view for the current dimension and  margins, if applicable* @param childDimension How big the child wants to be in the current    dimension* @return a MeasureSpec integer for the child*/public static int getChildMeasureSpec(int spec, int padding, int childDimension) {int specMode = MeasureSpec.getMode(spec);int specSize = MeasureSpec.getSize(spec);int size = Math.max(0, specSize - padding);int resultSize = 0;int resultMode = 0;switch (specMode) {// Parent has imposed an exact size on uscase MeasureSpec.EXACTLY:if (childDimension >= 0) {resultSize = childDimension;resultMode = MeasureSpec.EXACTLY;} else if (childDimension == LayoutParams.MATCH_PARENT) {// Child wants to be our size. So be it.resultSize = size;resultMode = MeasureSpec.EXACTLY;} else if (childDimension == LayoutParams.WRAP_CONTENT) {// Child wants to determine its own size. It can't be// bigger than us.resultSize = size;resultMode = MeasureSpec.AT_MOST;}break;// Parent has imposed a maximum size on uscase MeasureSpec.AT_MOST:if (childDimension >= 0) {// Child wants a specific size... so be itresultSize = childDimension;resultMode = MeasureSpec.EXACTLY;} else if (childDimension == LayoutParams.MATCH_PARENT) {// Child wants to be our size, but our size is not fixed.// Constrain child to not be bigger than us.resultSize = size;resultMode = MeasureSpec.AT_MOST;} else if (childDimension == LayoutParams.WRAP_CONTENT) {// Child wants to determine its own size. It can't be// bigger than us.resultSize = size;resultMode = MeasureSpec.AT_MOST;}break;// Parent asked to see how big we want to becase MeasureSpec.UNSPECIFIED:if (childDimension >= 0) {// Child wants a specific size... let him have itresultSize = childDimension;resultMode = MeasureSpec.EXACTLY;} else if (childDimension == LayoutParams.MATCH_PARENT) {// Child wants to be our size... find out how big it should// beresultSize = 0;resultMode = MeasureSpec.UNSPECIFIED;} else if (childDimension == LayoutParams.WRAP_CONTENT) {// Child wants to determine its own size.... find out how// big it should beresultSize = 0;resultMode = MeasureSpec.UNSPECIFIED;}break;}return MeasureSpec.makeMeasureSpec(resultSize, resultMode);}

  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 & LAYOUT_REQUIRED) == LAYOUT_REQUIRED ) {if (ViewDebug. TRACE_HIERARCHY) {ViewDebug. trace( this, ViewDebug.HierarchyTraceType.ON_LAYOUT );}onLayout(changed, l, t, r, b);//调用onLayout方法mPrivateFlags &= ~LAYOUT_REQUIRED ;if (mOnLayoutChangeListeners != null) {ArrayList<OnLayoutChangeListener> listenersCopy =(ArrayList<OnLayoutChangeListener>) 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);//通知对象的listener调用onLayoutChange}}}mPrivateFlags &= ~FORCE_LAYOUT ;}     

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

 @Overridepublic final void layout(int l, int t, int r, int b) {if (mTransition == null || !mTransition.isChangingLayout()) {super.layout</strong>(l, t, r, b);//调用父类view的layout方法</strong>} else {// record the fact that we noop'd it; request layout when transition finishesmLayoutSuppressed = true;}}

调用父类view的layout方法，再看onLayout方法   

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

  void layoutVertical() {// ....     for (int i = 0; i < count; i++) {final View child = getVirtualChildAt(i);if (child == null) {childTop += measureNullChild(i);} else if (child.getVisibility() != GONE) {childTop += lp. topMargin ;setChildFrame</strong>(child, childLeft, childTop + getLocationOffset(child),childWidth, childHeight);childTop += childHeight + lp. bottomMargin + getNextLocationOffset(child);i += getChildrenSkipCount(child, i);}}}

    private void setChildFrame(View child, int left, int top, int width, int height) {       child.layout(left, top, left + width, top + height);}

   protected void onLayout( boolean changed, int left, int top, int right, int bottom) {final int count = getChildCount();        for (int i = 0; i < count; i++) {final View child = getChildAt(i);if (child.getVisibility() != GONE) {final LayoutParams lp = (LayoutParams) child.getLayoutParams();final int width = child.getMeasuredWidth();final int height = child.getMeasuredHeight();                    ..switch (absoluteGravity & Gravity.HORIZONTAL_GRAVITY_MASK ) {..}switch (verticalGravity) {..}child.layout</strong>(childLeft, childTop, childLeft + width, childTop + height);}}}   

   // Step 3, draw the contentif (!dirtyOpaque) onDraw(canvas);其中onDraw实现:空实现。因为view怎样展示是由具体的view自行实现。protected void onDraw(Canvas canvas) {}// Step 4, draw the childrendispatchDraw(canvas);

protected void dispatchDraw(Canvas canvas) {  }也是空实现，因为view中没有子view，也就不需要向子view派发draw请求了，所以是空实现。

   protected void dispatchDraw(Canvas canvas) {final int count = mChildrenCount;final View[] children = mChildren ;int flags = mGroupFlags ;       ..          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</strong>(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</strong>(canvas, child, drawingTime);}}}// Draw any disappearing views that have animationsif (mDisappearingChildren != null) {final ArrayList<View> disappearingChildren = mDisappearingChildren ;final int disappearingCount = disappearingChildren.size() - 1;// Go backwards -- we may delete as animations finishfor (int i = disappearingCount; i >= 0; i--) {final View child = disappearingChildren.get(i);more |= drawChild</strong>(canvas, child, drawingTime);}}..}