Mirror (flip) a View / ProgressBar

问题

I have a custom built circular progress bar used for a seconds counter on a clock, which I'd like to flip, so that the clock is counting counter-clockwise.

Searching here for a solution, I found this:

Right to Left ProgressBar?

Which obviously works for a horizontal progress bar, but I can't simply rotate it 180 degrees, since that will just move the clock 180 degrees and it will still be ticking clockwise.

Is there any other way to mirror a ProgressBar, or any View?

Edit:

Just found "android:rotationY" and the programmatic equivalent, but this ideally needs to be for 2.2 and above..

回答1:

I was able to flip ProgressBar simply with attribute scaleX in XML:

android:scaleX="-1"

This works for other View as well.

回答2:

Extend ProgressBar in the same way you would for a horizontal progress bar, but in the onDraw method, flip the canvas rather than rotate it:

public class InverseProgressBar extends ProgressBar {

public InverseProgressBar(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);
}

public InverseProgressBar(Context context, AttributeSet attrs) {
    super(context, attrs);
}

public InverseProgressBar(Context context) {
    super(context);
}

@Override
protected synchronized void onDraw(Canvas canvas) {
    canvas.scale(-1f, 1f, super.getWidth() * 0.5f, super.getHeight() * 0.5f);
    super.onDraw(canvas);
}

}