Android View bizarre behaviour

Question

I have this bizarre behaviour when calling invalidate. I have made a custom viewgroup containing a bunch of imageviews.

I set up a onTouch listener with the on touch method to scroll the view. I know all the code is correct in terms of distances to scroll etc. by using logcat.

Now, for some reason the onLayout method is not being called after I call this.invalidate(). When I try to scroll, nothing changes on the screen. However, after I pause the activity and resume it, the screen will have shifted by the amount I scrolled.

I am not blocking the UI thread because there is nothing to block it with. In any case, I have tried postInvalidate() and nothing has worked.

Anybody have any bloody idea what's going on?

• Xaver Kapeller: invalidate() just redraws the View. It doesn't relayout anything. You need to call requestLayout() to start a new layouting process.

Answer 1

invalidate() does not relayout the view, it only causes the view to be redrawn. If you want to relayout it (which will invoke onLayout()) you also have to make a call to requestLayout().

• Kongo: I see! How did you come across that information? So invalidate calls onDraw()?
• Kongo: Also, do you have any idea how scrollview makes the view scroll smoothly? At the moment, it seems like I need to wait for the MotionEvent.ACTION_UP before it calls onLayout. Am I blocking the UI thread somehow?
• Floern: You can find more information in the documentation of these methods. A ScrollView does not re-layout its content, it's rather complicated. You could have a look into the ScrollView source code: grepcode.com/file/repository.grepcode.com/java/ext/…