Canvas and Drawables 翻譯第三集

Android官方原文地址：http://developer.android.com/guide/topics/graphics/2d-graphics.html

------以下的翻譯融入了自己的思考，便於理解，很多地方翻譯並不是很恰當，所以配上了英文原文

[title3]
On a View 在視圖組件上（View）上[/title3]

If your application does not require a significant amount of processing or frame- rate speed (perhaps for a chess game, a snake game, or another slowly-animated application), then you should consider creating a custom View component and drawing with a Canvas
in

f

is that the Android framework will provide you with a pre-defined Canvas to which you will place your drawing calls.

如果你的應用不需要大量的處理或沒有幀速率要求，像棋牌類遊戲、貪吃蛇、或者慢動畫應用，你可以考慮建立一個自訂視圖元件（View）並且使用畫板（Canvas）在View.onDraw()方法裡繪製。這樣做最大的方便之處在於Android框架層將為你提供一個預先定義好的畫板（Canvas），你可以使用該Canvas進行繪製。

To start, extend the

View.onDraw()

class (or descendant

thereof) and define the

View

callback

method. This method will be called by the Android framework request that sage sem the Android objalled by the Android fr all your calls to draw through the

onDraw()

,

which is passed to you through the

Canvas

callback.

首先，繼承View類別（或子類別），並且定義onDraw（）回調方法。這個方法將會被Android框架層調用，使得你的View繪製自己。在這個地方將要執行你需要的所有繪製調用，並且Canvas會透過onDraw（）回呼方法傳入。

The Android framework will only call

onDraw()

as necessary. Each time that your application is prepared to be drawn, you must request your View be invalidated by calling

onDraw()

.

This indicates that you'd like your View to be drawn and Android will then call your

onDraw()

method (though is not guaranteed that the callback will be instantaneous).

Android框架层只会在需要的时候调用onDraw（）方法。每次当你的应用准备好需要去绘制的时候，你必须通过invalidate（）方法使你的View无效。这表示你想要你的View被绘制并且Android将要回调你的onDraw（）方法(不保证这个回调将会被及时执行)

Inside your View component's

onDraw()

, use the Canvas given to you for all your drawing, using various

Canvas.draw...()

methods,
or other class

draw()

methods that take your Canvas as an argument. Once your

onDraw()

is complete, the Android
framework will use your Canvas to draw a Bitmap handled by the system.

在你的View组件里的onDraw（）方法中，使用给你的Canvas作你所有的绘制，使用各种各样的Canvas.draw...（）方法，或者其他类的Draw（）方法，这个类能够把给你的Canvas作为参数传入。一旦你的onDraw（）方法完成，Android框架将要用你的Canvas去绘制一张位图。

Note: In order to request an invalidate from a thread other than your main Activity's thread, you must call

postInvalidate()

.

For information about extending the

View

class,
read Building Custom Components.

注意：你如果要从主Activity的线程外的线程中使View无效，你必须调用postInvalidate（）方法，更多关于继承View类的信息，请阅读Building
Custom Components。

For a sample application, see the Snake game, in the SDK samples folder:

<your-sdk-directory>/samples/Snake/

.

一个程序示例，贪吃蛇游戏，放在SDK示例文件夹中，路径：

<your-sdk-directory>/samples/Snake/

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