为什么我在画布上的位图出现在背景可绘制对象下方？

Question

我有一个SurfaceView，我在其中设置背景颜色和图像，如下所示：

BitmapDrawable tiledBackground = new BitmapDrawable(BitmapFactory.decodeResource(getResources(), R.drawable.background));
tiledBackground.setTileModeX(Shader.TileMode.REPEAT);
tiledBackground.setColorFilter(0xaacceeff, PorterDuff.Mode.DST_OVER);
this.setBackgroundDrawable(tiledBackground);

我还有一个动画线程，我正在其中绘制图像（连续调整其 x 坐标，使其看起来向左移动）。背景图像是透明的 PNG，因此其中的某些部分是透明的。我从线程中绘制的图像似乎出现在SurfaceView 上的可绘制背景下方。我怎样才能让它出现在背景之上？我正在像这样绘制图像：

private void doDraw(Canvas canvas) {
    canvas.drawColor(Color.BLACK);
    canvas.drawBitmap(missile, x, getHeight() - 95, paint);
    canvas.restore();
}

missile和paint在线程的构造函数中初始化为：

missile = Bitmap.createBitmap(BitmapFactory.decodeResource(getResources(), R.drawable.missile));
paint = new Paint();

Answer 1

对 doDraw 的每次调用都应绘制您想要显示的所有内容，包括背景。

// Add to initializer
tiledBackground = new BitmapDrawable(BitmapFactory.decodeResource(getResources(), R.drawable.background));
tiledBackground.setTileModeX(Shader.TileMode.REPEAT);
tiledBackground.setColorFilter(0xaacceeff, PorterDuff.Mode.DST_OVER);

private void doDraw(Canvas canvas) {
    canvas.drawColor(Color.BLACK);
    // Create a rectangle (just holds top/bottom/left/right info)
    Rect drawRect = new Rect(); 

    // Populate the rectangle that we just created with the drawing area of the canvas.
    canvas.getClipBounds(drawRect);

    // Make the height of the background drawing area equal to the height of the background bitmap
    drawRect.bottom = drawRect.top + tiledBackground.getBitmap().getHeight();

    // Set the drawing area for the background.
    tiledBackground.setBounds(drawRect);

    tiledBackground.draw(canvas);
    canvas.drawBitmap(missile, x, getHeight() - 95, paint);
    canvas.restore();
}