为什么 Android 地图指南针演示使用 SmoothCanvas 类的委托？
在 Eclipse 中针对 Google API 提供的 Android MapsDemo 中，他们在 MapViewCompassDemo.java 中创建了一个内部类 SmoothCanvas。在此类中，重新实现了几乎所有方法，并将其重新路由到 Canvas 的委托实例。
static final class SmoothCanvas extends Canvas {
Canvas delegate;
private final Paint mSmooth = new Paint(Paint.FILTER_BITMAP_FLAG);
public void setBitmap(Bitmap bitmap) {
delegate.setBitmap(bitmap);
}
public void setViewport(int width, int height) {
delegate.setViewport(width, height);
}
...
在这种情况下，委托的意义何在？
In the Android MapsDemo available in Eclipse for the Google API, they create an inner class SmoothCanvas in MapViewCompassDemo.java. Within this class the re-implement seemingly every method and reroute it to a delegate instance of Canvas.
static final class SmoothCanvas extends Canvas {
Canvas delegate;
private final Paint mSmooth = new Paint(Paint.FILTER_BITMAP_FLAG);
public void setBitmap(Bitmap bitmap) {
delegate.setBitmap(bitmap);
}
public void setViewport(int width, int height) {
delegate.setViewport(width, height);
}
...
What is the point of the delegate in this instance?
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delegate的值被传递给dispatchDraw。SmoothCanvas类是delegate的包装器。通过委托，传递给dispatchDraw的Canvas实现会完成所有繁重的工作。包装器只允许注入平滑的油漆，而不实现 Canvas 的所有逻辑。The value of
delegateis passed in todispatchDraw. TheSmoothCanvasclass is a wrapper arounddelegate. By delegating, theCanvasimplementation passed todispatchDrawdoes all the heavy lifting. The wrapper just allows the injection of the smoothed paint without implementing all the logic ofCanvas.在这种情况下委托的关键点是：
通过激活该标志，绘制位图基本上会提高其性能。在示例中，您将在每个
drawBitmap调用中使用mSmoth。The key point of delegating in that instance is:
By activating that flag, drawing bitmaps will basically increase its performance. You will in the example that
mSmothis used in everydrawBitmapcall.