how to animate first in a viewWillTransitionToSize using animateAlongsideTransition

Question

I am trying to update my willAnimateRotationToInterfaceOrientation code to use the new viewWillTransitionToSize as a part of IOS 9.

In my app, I have two totally separate views for landscape and portrait (they are laid out differently, in a different pattern).

During rotation the self.view of the viewcontroller is assigned to the correct view (landscape or portrait). In IOS 9 using viewWillTransitionToSize, this revealed a timing race condition between the rotation animation and the assignment of the self.view.

The assignment of self.view = portraitView or self.view = landscapeView could happen either before the rotation, or after the rotation. It appears that because a view assignment is not an "animatable" property that it is executed at any time during the animateWithDuration window.

How do I force the view assignment to happen before the rotation animation?

- (void)viewWillTransitionToSize:(CGSize)size withTransitionCoordinator:(id <UIViewControllerTransitionCoordinator>)coordinator
 {

 UIInterfaceOrientation oldOrientation = [[UIApplication sharedApplication] statusBarOrientation];
 UIInterfaceOrientation orientation = [Utilities orientationByTransforming:[coordinator targetTransform] fromOrientation:oldOrientation];
 [coordinator animateAlongsideTransition:^(id<UIViewControllerTransitionCoordinatorContext> context)
 {

    [UIView animateWithDuration:[context transitionDuration] animations:^{
         if (UIInterfaceOrientationIsLandscape(orientation)) {
                self.view = self.landscapeView;
         }
         else{
                self.view = self.portraitView;
         }
     } completion:^(BOOL finished){
         //no completion logic for animateWithDuration
     }];
 } completion:^(id<UIViewControllerTransitionCoordinatorContext> context)
 {
     //no completion logic for animateAlongsideTransition
 }];

 [super viewWillTransitionToSize:size withTransitionCoordinator:coordinator];
}

Daniel Broad Daniel Broad · Accepted Answer · 2015-11-09T17:33:09

I think you need to have both views available:

[self.view addSubview: self.landscapeView];
[self.view addSubview: self.portraitView];

And then fade between them

self.landscapeView.alpha = self.portraitView.alpha = 0.0f;
[UIView animateWithDuration:[context transitionDuration] animations:^{
         if (UIInterfaceOrientationIsLandscape(orientation)) {
                self.landscapeView.alpha = 1.0f;
         }
         else{
                self.portraitView.alpha = 1.0f;
         }

how to animate first in a viewWillTransitionToSize using animateAlongsideTransition

1 Answers