Call rootViewController to switch views within content view (iOS)

I'm working on a pretty simple multiview app for the iOS and I've been following a great tutorial in an Apress book. I've basically got my rootViewController instantiated and displayed with the app dele开发者_JAVA百科gate, and I've got a number of content viewControllers (6) which I'd like to swap in and out based on user input. However, in the book they perform their switches with a button on a toolbar placed in the rootView using Interface Builder. It fires a method in rootView that loads up the new content ViewController and displays it.

My problem is that I'd like to perform the content view switch (that lies in my rootViewController instance), but I'd like to trigger the switch action with a button that's in my content view (and is therefore unavailable as my File Owner is my contentViewController, whose reference is held inside my rootViewController).

Hopefully I've explained it well enough, please let me know if I should elaborate more. I appreciate any help!

You need to pass down a reference to your root view controller (RootViewController *rootViewController) when you create your content view either in a custom init method or by just assigning it after you created it: self.contentView.rootViewController = self;.

Now inside your content view you can then call the appropriate method in the root view controller to do the switch: [self.rootViewController switchView]. This call then can be triggered inside the method that is called when you press the button (IBAction method).

So this is what you need to do: 1) Create a property inside the your content view controller of type RootViewController

@class RootViewController;

@interface MyContentViewController : NSObject {
@private
    RootViewController *rootViewController;
}

@property (retain) RootViewController *rootViewController;

and make sure it retains the reference. 2) Synthesis the property and add the callback to the root view controller that switches the view:

@implementation MyContentViewController

@synthesize rootViewController;

- (IBAction) switchView:(id) sender {
    [rootViewController switchToNextView];
}

-(void) dealloc {
    [rootViewController release];
    [super dealloc];
}

Also release your retain reference at the end.

3) Assign the root view controller to the content view inside your RootViewController:

self.contentViewController = [[[MyContentViewController alloc]
                         initWithNibName:@"ContentView" 
                         bundle:nil] autorelease];
self.contentViewController.rootViewController = self;

That should be all. I hope that helps you.

Well, you could simply create an IBAction in each of your child controllers that calls:

 [self.parentViewController switchToDifferentController:(int) viewNumber]

and then implement the switchToDifferentController method in your root. Other than ignore the compiler warning that parentView might not implement that method, it might work.

However, that is a bit brittle, as you'd have to assume that it was the parent calling you and that nobody will forget to implement that method.

In general, you use the "delegate" concept for a child controller to ask its parent to do something. The general idea is that you declare a group of methods as a "protocol". Think of it as a contract between objects. One object can say "I promise to implement these methods," and another can then choose to send those messages to it. The contract allows the compiler/system to check for conformance. You'll see this in UITableView, where the OS provides a standard table, but it calls back to your code to provide the individual cells as needed.

To implement a protocol, you mustdo the following: (See code segments below

1. Declares a protocol for the conversation
2. Specify that the parent will follows that protocol
3. Create a delegate property in your child
4. When the parent is about to launch the child, it assigns itself as the delegate for that child.
5. When the child wants to switch, it calls the parent using that protocol

@protocol myVCDelegate
    - (void)switchToDifferentController:(int) viewNumber ;
@end


@interface ParentViewController : UIViewController <VCDelegate>

@property(nonatomic, assign) id <VCDelegate> delegate

childController.delegate = self;

[self.delegate switchToDifferentController:kController5];