1、當測量好一個View后就可以重寫onDraw()方法，并在Canvas對象上繪制所需的圖形。

public class Canvas extends Object
java.lang.Object ???? android.graphics.CanvasCanvas()Construct an empty raster canvas. Canvas(Bitmap bitmap)Construct a canvas with the specified bitmap to draw into. ? Class Overview

The Canvas class holds the "draw" calls. To draw something, you need 4 basic components: A Bitmap to hold the pixels, a Canvas to host the draw calls (writing into the bitmap), a drawing primitive (e.g. Rect, Path, text, Bitmap), and a paint (to describe the colors and styles for the drawing).

?

2、onDraw

?protected void onDraw (Canvas canvas)

Implement this to do your drawing.

參數(shù)Canvas canvas對象用來進行繪圖。

Canvas?canvas?=?new?Canvas(bitmap);

bitmap用來存儲所有繪制在Canvas上的像素信息。

由源碼：View的繪制過程有以下幾步：

1）繪制背景（background.draw(canvas)）

2)繪制自己（omDraw()）

3)繪制children(dispatchDraw)

4)繪制裝飾（onDrawScrollBars(for instance)）

View繪制過程的傳遞通過dispatchDraw來實現(xiàn)，遍歷調(diào)用所有子元素的draw方法，draw時間一層層傳遞下去。

?