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.Canvas

Public Constructors

	Canvas()Construct an empty raster canvas.
	Canvas(Bitmap bitmap)Construct a canvas with the specified bitmap to draw into.

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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).

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2、onDraw

?protected void onDraw (Canvas canvas)

Implement this to do your drawing.

參數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，遍歷調用所有子元素的draw方法，draw時間一層層傳遞下去。

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總結

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