View is not automatically being drawed when overriding dispatchDraw

I'm trying to mirror a LinearLayout. To get this work, I extended LinerLayout to create my own View component.

This is what it looks like:

    public class FlipLayout extends LinearLayout implements Runnable {
        private boolean isMirroring = true;
        private Handler handler;

        public FlipLayout(Context context) {
            super(context);
            this.setWillNotDraw(false);
        }

        public FlipLayout(Context context, AttributeSet attr) {
            super(context, attr);
            this.setWillNotDraw(false);
            handler = new Handler();
            handler.postDelayed(this, 30);

        }

        @Override
        protected void dispatchDraw(Canvas canvas) {
            canvas.save();
            if (isMirroring) {
                canvas.rotate(180, getWidth() / 2, getHeight() / 2);
            }
            super.dispatchDraw(canvas);
            canvas.restore();
        }

        @Override
        public boolean dispatchTouchEvent(MotionEvent event) {
            if (isMirroring)
                event.setLocation(getWidth() - event.getX(),
                        getHeight() - event.getY());
            return super.dispatchTouchEvent(event);
        }

        @Override
        public void run() {
            invalidate();
            handler.postDelayed(this, 30);
        }

    }

That class is working well, but only when implementing the Runnable interface and by calling invalidate() every few milliseconds.

If I only rotate the canvas without invalidating the view, the changes of the child views are not drawn. Now I'm wondering what's the reason for this behaviour and if theres a way to get it working without the Runnable/Handler implementation. If I remove the line canvas.rotate(...) the changes of the 开发者_StackOverflow社区child views are drawn correctly (this is for example a progressbar which is updating itself frequently.)

I hope someone can help! Thanks so much. Chris

It looks normal to me that changing a Gui dynamically would not update the screen. In any Gui framework, they require the programmer to manually request the redraw.

This is because if i change 10 items in my Gui, i don't want to redraw 10 times, but only once at the end. And the framework can't guess when i'm done refactoring the Gui. So i need to explicitely call a refresh method somehow.

Alternatively, you could invalidate you Gui directly when you're done rotating your stuff, and not in a separate thread.