Question

When the app is launched, I want to freeze UI for a second or so to get a precondition service (for example – location service) initialized. Is there a way to do that?

Answer 1

Just place a transparent UIView on top of the entire screen and have it intercept all touch events.

To intercept touch events, simply subclass a UIView and override

- (BOOL)pointInside:(CGPoint)point withEvent:(UIEvent *)event;

Usually inside that method you’d call super on it, but in this case you would just return YES:

- (BOOL)pointInside:(CGPoint)point withEvent:(UIEvent *)event
{
    return YES;
}

If you’d like to be really fancy you can add a synthesized property to the UIView subclass called shouldInterceptTouches and do something like this:

- (BOOL)pointInside:(CGPoint)point withEvent:(UIEvent *)event
 {
     return shouldInterceptTouches ? YES : [super pointInside:point withEvent:event];
 }

Also remember to make sure that your transparent view is above the other views.

Side-note: Apple’s Human Interface Guidelines don’t like it when you do stuff like that. A user will be confused and disappointed if your app is not responsive and it may cause them to quit the app if they think it’s frozen. You’re better off displaying some sort of UIActivityIndicatorView and disabling only the buttons absolutely necessary. Apple likes it when you do stuff like that in the background and allow the user to do other things, just in case it takes a while or fails.