BuildLayerFrameLayout.java 文件源码

@Override
protected void dispatchDraw(Canvas canvas) {
    super.dispatchDraw(canvas);
    if (mChanged && Build.VERSION.SDK_INT >= Build.VERSION_CODES.ICE_CREAM_SANDWICH) {
        post(new Runnable() {
            @Override
            public void run() {
                if (mAttached && Build.VERSION.SDK_INT >= Build.VERSION_CODES.ICE_CREAM_SANDWICH) {
                    final int layerType = getLayerType();
                    // If it's already a hardware layer, it'll be built anyway.
                    if (layerType != LAYER_TYPE_HARDWARE || mFirst) {
                        mFirst = false;
                        setLayerType(LAYER_TYPE_HARDWARE, null);
                        buildLayer();
                        setLayerType(LAYER_TYPE_NONE, null);
                    }
                }
            }
        });
        mChanged = false;
    }
    PaintFlagsDrawFilter pfd = new PaintFlagsDrawFilter(0, Paint.ANTI_ALIAS_FLAG | Paint
            .FILTER_BITMAP_FLAG);
    canvas.setDrawFilter(pfd);
}