Disable all Input while UIActivityIndicatorView spinning

You can call beginIgnoringInteractionEvents when you start the spinner

[[UIApplication sharedApplication] beginIgnoringInteractionEvents];

and endIgnoringInteractionEvents when you stop it.

[[UIApplication sharedApplication] endIgnoringInteractionEvents];

Just make sure your code always comes to the point where you call endIgnoringInteractionEvents, otherwise your app will freeze (from the users point of view).

Just an addition to rokjarc answer. Here an example of watchdog to keep app alive. You can call always with some critical interval, maybe 10 sec. And if you need to enable within 10 sec, just call "enable" method.

UIWindow * __weak mainWindow;

- (void)disableGlobalUserInteractionForTimeInterval:(NSTimeInterval)interval
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        mainWindow = [[[UIApplication sharedApplication] windows] lastObject];
    });

    [mainWindow setUserInteractionEnabled:false];

    if (interval > 0)
    {
        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(interval * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
            [self enableGlobalUserInteraction];
        });
    }
}

- (void)enableGlobalUserInteraction
{
    if (mainWindow)
    {
        [mainWindow setUserInteractionEnabled:true];
    }
}

In Swift 3.0:

To disable interaction:

UIApplication.shared.beginIgnoringInteractionEvents() 

To restore interaction:

UIApplication.shared.endIgnoringInteractionEvents()