UIAlertViewDelegate clickedButtonAtIndex: usefulness?

The UIAlertViewDelegate protocol defines two methods, alertView:clickedButtonAtIndex: and alertView:didDismissWithButtonIndex:, which seem to me to be identical in usefulness.

Why is there a clickedButtonAtIndex and a didDismissButtonWithIndex when they both do the same thing? I realize there is also a willDismissButtonWithIndex that happens before the alert view is dismissed, but is there any reason to use clickedButtonAtIndex instead of didDismissButtonWithIndex?

Answers


I found a more useful difference between the two:

When showing a UIAlertView, and the device goes to sleep, alertView:didDismissWithButtonAtIndex: gets called, even though the alert view is not actually dismissed. It is shown again once the device wakes up. alertView:clickedButtonAtIndex: is only called when the user clicks one of the buttons.


The alertView:clickedButtonAtIndex: is called when the user clicks a button on an alert view whereas the alertView:didDismissWithButtonIndex: is called after an alert view is dismissed from the screen. (See the UIAlertViewDelegate Protocol Reference.)

The difference is minimal but it allows you to do something before or after animation.


If the alert view disappears for any reason (including being covered by another UIAlertView, going to sleep, etc.), didDismissWithButtonAtIndex: is called. This can mean that the method can be called even without the user clicking on anything. This can lead to unexpected behaviour if you depend on this delegate callback to be called in response to the user actually clicking on a button. In this case clickedButtonAtIndex: is more useful.


I couldn't reproduce Ed's behaviour by locking my device with the alert view present on iOS 7.

However, the most important difference between alertView:clickedButtonAtIndex:, alertView:didDismissWithButtonIndex: and alertView:willDismissWithButtonIndex: is that the first method (clickedButtonAtIndex:) is only called when the user explicitly taps on a button on your alert view (hence 'clicked').

Is it possible that an alert view is dismissed without clicking on a button? Yes, you could programmatically hide an alert view using the UIAlertView method dismissWithClickedButtonIndex:animated:.

So, if you need some behavior to be always triggered upon the dismissal of the alert view—whether it was triggered by the user tapping on a button or triggered programmatically—then using the didDismissWithButtonIndex: and willDismissWithButtonIndex: makes more sense.


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