Segmented Controls Mangled During Initial Transition Animation

Introduction

Transition animations are an essential part of creating smooth and visually appealing user interfaces. In this article, we’ll delve into the details of how segmented controls behave during initial transition animations in iOS.

Background

When a view controller’s view is transitioning to a new view controller, the animation can cause some visual artifacts, such as mangled or distorted views. Segmented controls, in particular, can exhibit this behavior when switching between different modes.

To understand why this happens, let’s first look at how segmented controls work.

How Segmented Controls Work

A segmented control is a UI component that allows the user to select one of multiple options from a group of predefined values. In iOS, segmented controls are implemented using UISegmentedControl, which consists of multiple buttons arranged horizontally.

When the user interacts with a segmented control, the selected button is highlighted, and the other buttons are deselected. The control also maintains a hidden state, where the button that was previously deselected becomes visible again when the user switches to it.

Transitioning Segmented Controls

Now, let’s examine what happens when we transition between two view controllers with segmented controls.

When a new view controller is presented, the old one is dismissed, and its view is removed from the display. However, during this transition period, some subtle issues can arise:

The views are not fully initialized or rendered before being displayed.
The animation may cause visual artifacts, such as mangled or distorted views.

In our example case, we have two instances of a SideAViewController, which contains a segmented control. When switching between these view controllers, the segmented control’s behavior is affected by the transition animation.

Problem Description

The user reported that during the initial transition from one instance of SideAViewController to another, the segmented controls become “mangled” or distorted. This issue persisted even after using various optimization techniques, such as caching the view controller instance.

Code Inspection

To better understand the problem, let’s take a closer look at the code snippet provided:

- (IBAction)switchViews:(id)sender {
    [UIView beginAnimations:@"Transition Animation" context:nil];

    if (self.sideBViewController.view.superview == nil) // sideA is active, sideB is coming
    {
        if (self.sideBViewController == nil)
        {
            SideAViewController *sBController =
            [[SideAViewController alloc] initWithNibName:@"SideAViewController" bundle:nil];
            self.sideBViewController = sBController;
            [sBController release];
        }

        [UIView setAnimationDuration:sideAViewController.transitionDurationSlider.value];
        if ([sideAViewController.transitionAnimation selectedSegmentIndex] == 0)
        {
            // flip: 0 == left, 1 == right
            if ([sideAViewController.flipDirection selectedSegmentIndex] == 0)
                [UIView setAnimationTransition:UIViewAnimationTransitionFlipFromLeft
                                       forView:self.view
                                         cache:YES];
            else 
                [UIView setAnimationTransition:UIViewAnimationTransitionFlipFromRight
                                       forView:self.view
                                         cache:YES];
        }
        else 
        {
            // curl: 0 == up, 1 == down
            if ([sideAViewController.curlDirection selectedSegmentIndex] == 0)
                [UIView setAnimationTransition:UIViewAnimationTransitionCurlUp
                   forView:self.view
                     cache:YES];
            else 
                [UIView setAnimationTransition:UIViewAnimationTransitionCurlDown
                   forView:self.view
                     cache:YES];
        }

        if ([sideAViewController.animationCurve selectedSegmentIndex] == 0)
            [UIView setAnimationCurve:UIViewAnimationCurveEaseInOut];
        else if ([sideAViewController.animationCurve selectedSegmentIndex] == 1)
            [UIView setAnimationCurve:UIViewAnimationCurveEaseIn];
        else if ([sideAViewController.animationCurve selectedSegmentIndex] == 2)
            [UIView setAnimationCurve:UIViewAnimationCurveEaseOut];
        else if ([sideAViewController.animationCurve selectedSegmentIndex] == 3)
            [UIView setAnimationCurve:UIViewAnimationCurveLinear];

        [sideBViewController viewWillAppear:YES];
        [sideAViewController viewWillDisappear YES];
        [sideAViewController.view removeFromSuperview];
        [self.view insertSubview:sideBViewController.view atIndex:0];
        [sideBViewController viewDidAppear:YES];
        [sideAViewController viewDidDisappear:YES];
    }
}

In this code snippet, we can see that:

The segmented control’s selectedSegmentIndex is being used to determine the animation curve and transition effect.
The segmentation curve (sideAViewController.animationCurve) affects how the buttons are highlighted or deselected during the transition.

To fix the issue with mangled segmented controls, let’s explore alternative approaches for managing the transition between view controllers:

Optimization Techniques

Inserting Segmented Control at Lower Index
In our analysis, we discovered that inserting the sideBViewController at a lower index than sideAViewController resolves the issue.

- (IBAction)switchViews:(id)sender {
    [UIView beginAnimations:@"Transition Animation" context:nil];

    if (self.sideBViewController.view.superview == nil) // sideA is active, sideB is coming
    {
        if (self.sideBViewController == nil)
        {
            SideAViewController *sBController =
            [[SideAViewController alloc] initWithNibName:@"SideAViewController" bundle:nil];
            self.sideBViewController = sBController;
            [sBController release];
        }

        // Insert sideB at a lower index than sideA
        [self.view insertSubview:sideBViewController.view atIndex:0];

        [UIView setAnimationDuration:sideAViewController.transitionDurationSlider.value];
        if ([sideAViewController.transitionAnimation selectedSegmentIndex] == 0)
        {
            // flip: 0 == left, 1 == right
            if ([sideAViewController.flipDirection selectedSegmentIndex] == 0)
                [UIView setAnimationTransition:UIViewAnimationTransitionFlipFromLeft
                                       forView:self.view
                                         cache:YES];
            else 
                [UIView setAnimationTransition:UIViewAnimationTransitionFlipFromRight
                                       forView:self.view
                                         cache:YES];
        }
        else 
        {
            // curl: 0 == up, 1 == down
            if ([sideAViewController.curlDirection selectedSegmentIndex] == 0)
                [UIView setAnimationTransition:UIViewAnimationTransitionCurlUp
                   forView:self.view
                     cache:YES];
            else 
                [UIView setAnimationTransition:UIViewAnimationTransitionCurlDown
                   forView:self.view
                     cache:YES];
        }

        if ([sideAViewController.animationCurve selectedSegmentIndex] == 0)
            [UIView setAnimationCurve:UIViewAnimationCurveEaseInOut];
        else if ([sideAViewController.animationCurve selectedSegmentIndex] == 1)
            [UIView setAnimationCurve:UIViewAnimationCurveEaseIn];
        else if ([sideAViewController.animationCurve selectedSegmentIndex] == 2)
            [UIView setAnimationCurve:UIViewAnimationCurveEaseOut];
        else if ([sideAViewController.animationCurve selectedSegmentIndex] == 3)
            [UIView setAnimationCurve:UIViewAnimationCurveLinear];

        [sideBViewController viewWillAppear:YES];
        [sideAViewController viewWillDisappear YES];
        [sideAViewController.view removeFromSuperview];
    }
}

By inserting the sideBViewController at a lower index, we ensure that it is displayed before the sideAViewController, which resolves the issue with mangled segmented controls.

Conclusion

Transitioning between view controllers can be challenging, especially when working with UI components like segmented controls. By understanding how these controls behave during transitions and applying optimization techniques, you can create smooth and visually appealing user interfaces.

In this article, we explored the issue of mangled segmented controls during transition animations in iOS. We analyzed the provided code snippet and discovered that inserting the segmented control at a lower index resolves the problem.

Last modified on 2024-01-06