android - View 中的多个 Canvas

Question

我已经重写了 onDraw() 方法，如下所示:

public void onDraw(Canvas canvas1){
Canvas canvas2 = new Canvas();

Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.graphic1);
Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.graphic2);

canvas1.drawBitmap(
          top,
          new Rect(0, 0, graphic1.getWidth(), graphic1.getHeight()),
          new Rect(0, 0, width, width),
          null);

canvas2.drawBitmap(
          top,
          new Rect(0, 0, graphic2.getWidth(), graphic2.getHeight()),
          new Rect(0, 0, width, width),
          null);

}

仅显示 canvas1 上的 graphic1，不显示 canvas2 和 graphic2。如何让多个 Canvas 显示在一个 View 上？

Answer 1

正如评论所说，您没有将 Canvas2 附加到任何东西上。你在每一帧创建它(这很糟糕)，绘制它然后让它进入我们的范围以被垃圾收集。你应该做什么它在 View 的构造函数中创建带有支持位图的 Canvas2 并将其保留为成员。然后你可以绘制它，然后将它的位图 blit 到 Canvas1。例如:

public MyCustomView(Context context)
{
    super(context);
    _canvas2 = new Canvas(_backingBitmap);
}

public void onDraw(Canvas canvas1)
{
Bitmap graphic1 = BitmapFactory.decodeResource(getResources(), R.drawable.graphic1);
Bitmap graphic2 = BitmapFactory.decodeResource(getResources(), R.drawable.graphic2);

canvas1.drawBitmap(
          top,
          new Rect(0, 0, graphic1.getWidth(), graphic1.getHeight()),
          new Rect(0, 0, width, width),
          null);

_canvas2.drawBitmap(
          top,
          new Rect(0, 0, graphic2.getWidth(), graphic2.getHeight()),
          new Rect(0, 0, width, width),
          null);

canvas1.drawBitmap(
          top,
          new Rect(0, 0, _backingBitmap.getWidth(), _backingBitmap.getHeight()),
          new Rect(0, 0, width, width),
          null);
}