Error in Component Width after Screen Rotation

Mr_Czechowski · December 20, 2022, 4:21pm

If you set a component's Width to a WidthPercent, the component's Width value is not updated in time for use in the ScreenOrientationChanged event.

ewpatton · December 20, 2022, 5:03pm

This is because of how percent dimensions are handled internally. In particular, the width/height computations for percentages are deferred for the next draw cycle that happens after the point at which the ScreenOrientationChanged event is run. I think it should be fixable by packaging that event up into its own runnable and scheduling that to happen immediately so that in terms of the event queue it will occur after the redraw of the screen is complete. The challenge will be understanding if this potentially breaks other apps that might be built around the current behavior.

Mr_Czechowski · December 20, 2022, 6:17pm

understanding if this potentially breaks other apps that might be built around the current behavior.

Is this a case of: Anything that was built on an incorrect value, was already broken?

Empathetically: The former dimension (pre-orientation-change) is what is currently returned. I suppose this value could be useful, however, I think this value could still be calculated by looking at the opposite current dimension (post-orientation-change).

Anke · December 20, 2022, 8:48pm

Mr_Czechowski · December 21, 2022, 4:00am

Thanks Anke. That is a possible work-around.

Anke · December 21, 2022, 1:19pm

I've been using a timer for the .ScreenOrientationChanged event for many years (in fact, since the beginning) in all my apps.

It takes some time (~100 ms) to capture the changes, so using a timer is essential.

Mr_Czechowski · December 22, 2022, 6:31pm

I've been using a timer for the .ScreenOrientationChanged event for many years...

Interesting. Is this a desirable behavior/work-around?

I'll be sure to use >100ms. Thanks for the heads up.

ewpatton · December 22, 2022, 6:43pm

I've never quite understood this decision, but there is a code-based reason for this:

github.com

mit-cml/appinventor-sources/blob/3d0ad63de092c6f41b96e9e794427ace4d151959/appinventor/components/src/com/google/appinventor/components/runtime/Form.java#L476


      
              }
            } else { // Portrait
              if (frameLayout.getHeight() >= frameLayout.getWidth()) {
                dispatchEventNow = true;
              }
            }
          }
          if (dispatchEventNow) {
            recomputeLayout();
            final FrameLayout savedLayout = frameLayout;
            androidUIHandler.postDelayed(new Runnable() {
                public void run() {
                  if (savedLayout != null) {
                    savedLayout.invalidate();
                  }
                }
              }, 100);          // Redraw the whole screen in 1/10 second
                                // we do this to avoid screen artifacts left
                                // left by the Android runtime.
            ScreenOrientationChanged();
          } else {

I'm not 100% sure that whatever reasons for the 100 ms delay is true any more. One thing I'm considering is moving the call to ScreenOrientationChanged into the delayed redraw operation so that the behavior is more consistent with people's expectations about what this event represents.