边看源码边参考别人的博客等，做一下学习笔记。

 

要了解View的绘制，首先得知道View树的结构：（可以参考http://blog.csdn.net/qinjuning/article/details/7226787）

 

整个 View 树的绘图流程在ViewRoot.java类的performTraversals()函数展开，其绘制流程如下：

我们从最基本的思路来理解绘图流程：先确定所有View的大小，然后根据布局决定每个View的位置，然后开画！

这里着重关注具体绘图的Draw方法，其绘制流程为：

View.draw(Canvas) 方法：

/**     * Manually render this view (and all of its children) to the given Canvas.     * The view must have already done a full layout before this function is     * called.  When implementing a view, implement     * {
    @link #onDraw(android.graphics.Canvas)} instead of overriding this method.     * If you do need to override this method, call the superclass version.     *     * @param canvas The Canvas to which the View is rendered.       *     * 根据给定的 Canvas 自动渲染 View（包括其所有子 View）。在调用该方法之前必须要完成 layout。当你自定义 view 的时候，     * 应该去是实现 onDraw(Canvas) 方法，而不是 draw(canvas) 方法。如果你确实需要复写该方法，请记得先调用父类的方法。     */    public void draw(Canvas canvas) {        / * Draw traversal performs several drawing steps which must be executed         * in the appropriate order:         *         *      1. Draw the background if need         *      2. If necessary, save the canvas' layers to prepare for fading         *      3. Draw view's content         *      4. Draw children (dispatchDraw)         *      5. If necessary, draw the fading edges and restore layers         *      6. Draw decorations (scrollbars for instance)         */     // Step 1, draw the background, if needed        if (!dirtyOpaque) {            drawBackground(canvas);        }         // skip step 2 & 5 if possible (common case)        final int viewFlags = mViewFlags;        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 2, save the canvas' layers        ...        // 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        // Step 6, draw decorations (scrollbars)        onDrawScrollBars(canvas);    }

ViewGroup.dispatchDraw()方法：

dispatchDraw(Canvas canvas){... if ((flags & FLAG_RUN_ANIMATION) != 0 && canAnimate()) {
   //处理 ChildView 的动画     final boolean buildCache = !isHardwareAccelerated();            for (int i = 0; i < childrenCount; i++) {                final View child = children[i];                if ((child.mViewFlags & VISIBILITY_MASK) == VISIBLE) {
   //只绘制 Visible 状态的布局，因此可以通过延时加载来提高效率                    final LayoutParams params = child.getLayoutParams();                    attachLayoutAnimationParameters(child, params, i, childrenCount);// 添加布局变化的动画                    bindLayoutAnimation(child);//为 Child 绑定动画                    if (cache) {                        child.setDrawingCacheEnabled(true);                        if (buildCache) {                            child.buildDrawingCache(true);                        }                    }                }            }     final LayoutAnimationController controller = mLayoutAnimationController;            if (controller.willOverlap()) {                mGroupFlags |= FLAG_OPTIMIZE_INVALIDATE;            }    controller.start();// 启动 View 的动画} // 绘制 ChildView for (int i = 0; i < childrenCount; i++) {            int childIndex = customOrder ? getChildDrawingOrder(childrenCount, i) : i;            final View child = (preorderedList == null)                    ? children[childIndex] : preorderedList.get(childIndex);            if ((child.mViewFlags & VISIBILITY_MASK) == VISIBLE || child.getAnimation() != null) {                more |= drawChild(canvas, child, drawingTime);            }        }...}protected boolean drawChild(Canvas canvas, View child, long drawingTime) {        return child.draw(canvas, this, drawingTime);}/**     * This method is called by ViewGroup.drawChild() to have each child view draw itself.     * This draw() method is an implementation detail and is not intended to be overridden or     * to be called from anywhere else other than ViewGroup.drawChild().     */    boolean draw(Canvas canvas, ViewGroup parent, long drawingTime) {        ...    }

 

参考资料：

http://codekk.com/blogs/detail/54cfab086c4761e5001b253f

http://blog.csdn.net/qinjuning/article/details/7110211

http://blog.csdn.net/xyz_lmn/article/details/20385049