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I have a view that creates a new core data managed object, and fills in all the required properties and also allows optional ones. I originally had a "Done" button on the top left, and when that was pressed, I validated the object then saved and removed the view.

Now I have an edit/done type setup on the top right, so sometimes there are two identical "Done" buttons on the top of the view. I want to switch the left side button so that it just has the normal "Back" button, then somehow validate and stop the view from being removed if it doesn't validate. I can't find any way to capture the method called by that back button and modify it, and viewWillDisappear doesn't work cause there's no way to abort the disappearing.

How can I make this work? I need to validate this, then save, then remove the view if validate and save worked only.

RedBlueThing
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Alex Gosselin
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2 Answers2

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There is no documented way to intercept the standard back button of UINavigationController. If you want this functionality, your only option would be to customize leftBarButtonItem with a custom button.

When the user taps that button, you can first validate your object and then call popViewControllerAnimated:.

It's hard to mimic the look of the built-in back button, though.

Ole Begemann
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It sounds like your view is a perfect candidate to be pushed modally instead of through the navigation controller stack.

Push the view that creates your NSManagedObject modally:

[self presentModalViewController:yourViewController animated:YES]

Then continue to use your top right EDIT/DONE button for editing/validation as you currently are and when validation is successful simply save your object and dismiss the modal view controller from the parent view controller:

[[self parentViewController] dismissModalViewControllerAnimated:YES];

For more details check http://developer.apple.com/library/ios/featuredarticles/ViewControllerPGforiPhoneOS/ModalViewControllers/ModalViewControllers.html#//apple_ref/doc/uid/TP40007457-CH111-SW14

If you still want to use a button on the left hand side perhaps you can change the right button to say EDIT/CANCEL and add a DONE button on the left side that is only visible when you're not in EDIT mode. If appropriate you can point the DONE button to run through the same validation process before dismissing the modal view using the code above but it probably makes sense that the EDIT/CANCEL button takes care of it.

I hope this helps. Rog

Rog
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  • I used a variation of your answer / part of it, making the Edit / Done button take care of saving seems to be the best solution. Thanks. – Alex Gosselin Nov 19 '10 at 04:35