UIVisualEffectView in iOS 10

iOS 10 has changed the way UIVisualEffectView works, and it has broken many use cases which were not strictly speaking "legal", but worked before. Sticking to documentation, you should not be fading in UIVisualEffectView, which is what happens when you use UIModalTransitionStyleCrossDissolve. It seems now broken on iOS 10, along with masking of visual effect views, and others.

In your case, I would suggest an easy fix which will also create a better effect than before, and is supported on both iOS 9 and 10. Create a custom presentation and instead of fading the view in, animate the effect property from nil to the blur effect. You can fade in the rest of your view hierarchy if needed. This will neatly animate the blur radius similar to how it looks when you pull the home screen icons down.

    UIView.animate(withDuration: 0.5) {        self.effectView.effect = UIBlurEffect(style: .light)    }

Tested on both iOS9 and 10. Works fine for me

Code below blur parent view controller when ViewController presented. Tested on both iOS9 and 10.

@interface ViewController () <UIViewControllerTransitioningDelegate, UIViewControllerAnimatedTransitioning>@property (nonatomic) UIVisualEffectView *blurView;@end@implementation ViewController- (instancetype)init{    self = [super init];    if (!self)        return nil;    self.modalPresentationStyle = UIModalPresentationOverCurrentContext;    self.modalTransitionStyle = UIModalTransitionStyleCrossDissolve;    self.transitioningDelegate = self;    return self;}- (void)viewDidLoad{    [super viewDidLoad];    self.view.backgroundColor = [UIColor clearColor];    self.blurView = [UIVisualEffectView new];    [self.view addSubview:self.blurView];    self.blurView.frame = self.view.bounds;}- (id <UIViewControllerAnimatedTransitioning>)animationControllerForPresentedController:(UIViewController *)presented                                                                       presentingController:(UIViewController *)presenting                                                                   sourceController:(UIViewController *)source{    return self;}-(NSTimeInterval)transitionDuration:(id<UIViewControllerContextTransitioning>)transitionContext{    return 0.3;}-(void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext{    UIView *container = [transitionContext containerView];    [container addSubview:self.view];    self.blurView.effect = nil;    [UIView animateWithDuration:0.3 animations:^{        self.blurView.effect = [UIBlurEffect effectWithStyle:UIBlurEffectStyleDark];    } completion:^(BOOL finished) {        [transitionContext completeTransition:finished];    }];}@end