Question

I have a UISegmentedControl that is shown/hide like a modal window. Initially it does not have a selected segment. In IB, the Value Changed event is wired to the method – (IBAction)cardClassificationChanged:(UISegmentedControl *)sender. Here is that method:

- (IBAction)cardClassificationChanged:(UISegmentedControl *)sender
{
    NSLog(@"%d", sender.selectedSegmentIndex);
    // block for updating the categorization of current card asynchronously
    [self.cardActionSheet hideWithAnimation];
}

If I comment out the last line (the call to -hideWithAnimation), the selection changes as expected, everything works. However, with the call to that animation method, the UISegmentedControl selection will not visually change before the animation. Here is the hideWithAnimation method:

- (void)hideWithAnimation
{
    CATransition *animation = [CATransition animation];
    animation.type = kCATransitionFade;
    animation.duration = globalAnimationLength;
    [self.layer addAnimation:animation forKey:nil];

    self.hidden = YES;
}

The next time this view appears (from a touch gesture), the UISegmentedControl will have the correct segment selected though.

It seems like I should not have to call setNeedsDisplay for the UISegmentedControl, but even when I experiment with it in the cardClassificationChanged method or the hideWithAnimation method, it does not refresh.

I’m obviously missing something related to the UI update, what do I need to call to update the UISegmentedControl selection before the animation?

Answer 1

I suggest you should use UIKit animations for fading out your control. Try the following code

- (void)hideWithAnimation
{
    [UIView animateWithDuration:0.2
                 animations:^{
                     self.alpha = 0.;
                 } completion:^(BOOL finished) {
                     self.alpha = 1.;
                     self.hidden = YES;
                 }];
}