Can I animate a view to fade in from hidden?

Question

I am trying to have a view scrim fade in on top of everything in my view controller after 5 seconds once the initial view loads. This is what I have right now.

- (void)viewDidLoad {


[super viewDidLoad];
// Do any additional setup after loading the view.

[self setupAlarmPoll];
[self setupTimeLabel];
self.shouldRefresh = YES;
[self refreshSpotifyToken];
[[NSNotificationCenter defaultCenter] addObserver:self
                                         selector:@selector(receiveNotification:)
                                             name:@"backHome"
                                           object:nil];

[[NSNotificationCenter defaultCenter] addObserver:self
                                         selector:@selector(receiveNotification:)
                                             name:@"applicationDidEnterBackground"
                                           object:nil];

dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 5.0 * NSEC_PER_SEC), dispatch_get_main_queue(), ^{

    [UIView animateWithDuration:2.00 animations:^{

       self.scrim.hidden = NO;
    }];



});

However, I don't get a gradual fade-in. The view just appears. How can I accomplish this animation in objective-c?

Answer 1

The hidden property of a view is not animatable. The alpha property, however, is animatable.You need to:

1. Set the alpha to zero
2. Set hidden to false.
3. Animate the alpha to 1.0

By doing that you make the view no longer hidden, but completely transparent. The you animate the alpha property from 0.0 to 1.0, making the view fade in as desired.

The code would look like this:

self.scrim.alpha = 0;
self.scrim.hidden = NO;
[UIView animateWithDuration:2.00 
  delay: 5.0
  options: 0
  animations:^{
   self.scrim.alpha = 1.0;
  }
  completion: nil
];

(Note that the long form of animateWithDuration takes a delay parameter, so you don't have to wrap it in a call to dispatch_after .)

Also, why are you doing new development in Objective-C?

Answer 2

Yes, but it isn't isHidden you are looking for, it's the alpha property of the view. You see, isHidden will just straight up declare if something is 100% not able to be seen at all or not. And as such you can not animate the isHidden property of a UIView . But this is where the alpha property comes to the rescue, because it is intended to be used exactly as you are trying to with isHidden . The alpha property determines how faded a UIView is on screen. So if the alpha is at 0 , it's hidden. So if you set your view's alpha to 0 then use the follow code you can fade in the view:

// Swift
UIView.animate(withDuration: 0.25) { 
    view.alpha = 1
}

// Objective-C
[UIView animateWithDuration:0.25 ^{
    self.view.alpha = 1.0;
}];

Answer 3

Either animate alpha as others have mentioned, or use transitionWithView with UIViewAnimationOptionTransitionCrossDissolve :

- (void)viewDidLoad {
    [super viewDidLoad];

    self.scrim.hidden = true;
}

- (void)viewDidAppear:(BOOL)animated {
    [UIView transitionWithView:self.scrim duration:2 options:UIViewAnimationOptionTransitionCrossDissolve animations:^{
        self.scrim.hidden = false;
    } completion:nil];
}