android - 如何使 Canvas 绘图区域在 android 中透明？

Question

我想让 Canvas 区域透明，因为我想在它后面添加一个图像，以便 Canvas 操作发生在图像上方。我的 Canvas 代码在这里

public class Panel extends SurfaceView implements SurfaceHolder.Callback {

private ViewThread mThread;
private ArrayList<Element> mElements = new ArrayList<Element>();

public Panel(Context context, AttributeSet attrs) { 
    super(context, attrs); 
    getHolder().addCallback(this); 
    mThread = new ViewThread(this); 
} 


public void doDraw(Canvas canvas) {
    canvas.drawColor(Color.TRANSPARENT);
    synchronized (mElements) {
        for (Element element : mElements) {
            element.doDraw(canvas);
        }
    }
}

@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
    // TODO Auto-generated method stub
}

@Override
public void surfaceCreated(SurfaceHolder holder) {
    if (!mThread.isAlive()) {
        mThread = new ViewThread(this);
        mThread.setRunning(true);
        mThread.start();
    }
}

@Override
public void surfaceDestroyed(SurfaceHolder holder) {
    if (mThread.isAlive()) {
        mThread.setRunning(false);
    }
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    synchronized (mElements) {
        mElements.add(new Element(getResources(), (int) event.getX(), (int) event.getY()));
    }
    return super.onTouchEvent(event);
}

如何实现它，上面的任何 fragment 都会非常有帮助。谢谢

Answer 1

我得到了输出

 public Panel(Context context, AttributeSet attrs) { 
    super(context, attrs); 
    this.setBackgroundColor(Color.TRANSPARENT);                 
    this.setZOrderOnTop(true); //necessary                
    getHolder().setFormat(PixelFormat.TRANSPARENT); 
    getHolder().addCallback(this); 
    mThread = new ViewThread(this); 

}