Nikola Zdravevski's Blog

I'm that guy who brought 21.5'' iMac all the way from Jersey to Macedonia as carry-on baggage.

UINavigationController Back Button Custom Action (Quick Tip)

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We all know the good, old UINavigationController that is used in almost every iOS application. UINavigationController has a default action when back button is pressed on one of its stack’s view controllers i.e. - go back one level in the navigation stack. However, there are cases when we need to do something extra when back button is pressed. For example - and this is just an example usage, if we want to mimic combo box - like control in iOS (which is usually implemented via single, right detail UITableViewCell in the parent = table view cell with style UITableViewCellStyleValue1) and we do the selection by pushing a new, child view controller with a checkbox enabled UITableView.

Such an implementation can be found in the stock Settings.app if we choose Sounds and if we take a look at the Ringtone right detail UITableViewCell. That is a combo box - like structure and selecting it brings a new, child view controller with selection logic.




In such a scenario, what I like to do is set the parent’s right detail UITableViewCell with the selected value from the child UITableView when the back button on the child view controller is pressed. That way I don’t have to set the selected value on every selection user does in the child UITableView (at tableView: didSelectRowAtIndexPath: with a call to the delegate) so I only do the setting once, at the end. I was having trouble finding the right & correct place to put the delegate call that sets the selected value on the parent and finally after some thinking around, I ended up with this awesome spot to put your back button action call.

Where to put your back button action method call
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- (void)viewWillDisappear:(BOOL)animated
{
    if ([self.navigationController.viewControllers indexOfObject:self] == NSNotFound) {
        [self.delegate setParentSelectedCity:self.selectedCity];
    }
    [super viewWillDisappear:animated];
}

This code should be put in the child view controller and it ensures us that back button has been pressed because self is no longer in the UINavigationController stack. What I also have here is my setParentSelectedCity: delegate method that sets the parent’s right detail UITableViewCell. self.selectedCity is a property that holds the selected value by the user.


Of course, you can put whatever method call you want on that place.

Thanks for reading my post, I hope it may be of any help.

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