1、當(dāng)測(cè)量好一個(gè)View后就可以重寫(xiě)onDraw()方法，并在Canvas對(duì)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).

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2、onDraw

?protected void onDraw (Canvas canvas)

Implement this to do your drawing.

參數(shù)Canvas canvas對(duì)象用來(lái)進(jìn)行繪圖。

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

bitmap用來(lái)存儲(chǔ)所有繪制在Canvas上的像素信息。

由源碼：View的繪制過(guò)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(guò)程的傳遞通過(guò)dispatchDraw來(lái)實(shí)現(xiàn)，遍歷調(diào)用所有子元素的draw方法，draw時(shí)間一層層傳遞下去。

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