iPhone: Switching Views From Outside Root Controller

Question

I am using a UINavigationController to switch between views. What I would like is for each view to have the ability to control when it is swapped out for another view by having buttons within the view. All of the samples I've seen thus far have placed buttons on a toolbar, which is located on the root view containing the Switch View Controller rather than the views, them self. Is it possible to do what I want? I can't figure how to wire up the connection back to the UINavigationController.

I'm having a difficult time wording this, so please feel free to let me know if you need additional clarification.

Answer 1

Read about delegates. Delegates are a common method to signal stuff from objects to their "parents" or any other objects.

You should have a "delegate" property (can really be called anything, this is just a convention) on your child views. You can have buttons in your child views.

You declare the delegate like this:

interface ChildView : UIViewController {
    id delegate;
}

@property (assign) id delegate;

implementation ChildView

@synthesize delegate;

Then, when you set up your child views inside your UINavigationController, you do:

ChildView *childView = [[ChildView alloc] init...]
childView.delegate = self;

Inside your child view, you have a button method:

- (IBAction) didPressButton:(id)sender {
    [self.delegate didPressButtonToSwapView];
}

Inside your UINavigationController, you have a method:

- (void) didPressButtonToSwapView {
    [self popViewController]; // use the right names, I made these up :)
    [self pushAnotherViewController];
}

You should also read about protocols which would make the above code more robust and would help you make sure you only call the right methods on delegate, but I did not want to complicate this example.

EDIT: yes, the cleanest way to get rid of the warning is to use a protocol. Just put this in a separate .h file:

@protocol SwitchingDelegate
- (void) didPressButtonToSwapView;
@end

Include this .h in the UINavController header, and say the UINavController implements the protocol:

@interface MyNav: UINavController <SwitchingDelegate> { ...

Implement the method in the implementation (you don't need anything more in the interface).

In your ChildView, say that the delegate must implement the protocol: change all the declarations to:

id<SwitchingDelegate> delegate;

The compiler then helps you by checking whether the delegate objects really implement the protocol. You should not get any warnings when you have completed all of this correctly.