public void draw(Canvas canvas) {
	/*
     * 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)
     *      7. If necessary, draw the default focus highlight
     */

	// Step 1, draw the background, if needed
    int saveCount;
	drawBackground(canvas);

    // ……代码省略……

	// Step 2, save the canvas' layers
   	// ……代码省略……
    
    // Step 3, draw the content
    onDraw(canvas);

    // Step 4, draw the children
    dispatchDraw(canvas);

    // Step 5, draw the fade effect and restore layers
    // ……代码省略……

    // Step 6, draw decorations (foreground, scrollbars)
    onDrawForeground(canvas);

    // Step 7, draw the default focus highlight
    drawDefaultFocusHighlight(canvas);

    // ……代码省略……
}

private void drawBackground(Canvas canvas) {
    // ……代码省略……
}

protected void onDraw(Canvas canvas) {
}

protected void dispatchDraw(Canvas canvas) {
}

public void onDrawForeground(Canvas canvas) {
    // ……代码省略……
}