Pushing and Popping ViewControllers using a Navigation Controller: Implementation

Like many others I started to code an experiment today where I would have two view controllers and be able to switch between them. I got this to work using a navigation controller, but I have a question about the implementation.

In my TwoViewsAppDelegate, I define the navigation controller and the rootViewController.

@interface TwoViewsAppDelegate : NSObject <UIApplicationDelegate> {
    UIWindow *window;
    UINavigationController *navigationController;
    RootViewController *rootViewController;
}

and set them up as follows:

- (BOOL)application:(UIApplication *)application     didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {    

    rootViewController = [[RootViewController alloc] init];
    navigationController = [[UINavigationController alloc] initWithRootViewController:rootViewController];
    [window setRootViewController:navigationController];
    [self.window makeKeyAndVisible];

    return YES;
}

Then in my rootViewController, I define th开发者_如何学Goe level2ViewController that I am going to switch to, and a button that I'm going to press to make the switch happen:

@interface RootViewController : UIViewController {

    UIButton *theButton;
    Level2ViewController *level2ViewController;
}

Here's the response to the button being pressed in RootViewController.m:

-(void)level1ButtonPressed:(id)sender
{
    if (level2ViewController == nil)
    {
        level2ViewController = [[Level2ViewController alloc] init];
    }

    [self.navigationController pushViewController:level2ViewController animated:YES];
}

The problem is that if there was going to be a level3ViewController, it would have to be defined as a member of level2ViewController, etc. for however many view controllers i wanted to push onto the stack.

It would be nice to be able to define all the view controllers in one place, preferably the app Delegate. Is this possible?

---

To solve this, you can create a callback-type method which uses the delegate of the class that'll be sending the requests for the view controllers. Best explained through code...

RootViewController.h

#import "RootInterfaceView.h"
// all the other VC imports here too
@interface RootViewController : UIViewController <RootInterfaceViewDelegate>
{
    RootInterfaceView *interface;
}

RootViewController.m

-(void)rootInterfaceView: (RootInterfaceView*)rootInterfaceView didSelectItem:(NSUInteger)itemTag
{
    switch (itemTag)
    // then create the matching view controller
}

RootInterfaceView.h

// imports here if required
@protocol RootInterfaceViewDelegate;

@interface RootInterfaceView : UIView <RootInterfaceItemViewDelegate>
{
    id <RootInterfaceViewDelegate> delegate;
}

@property (nonatomic, assign) id delegate;

@end

@protocol RootInterfaceViewDelegate <NSObject>

@optional
-(void)rootInterfaceView: (RootInterfaceView*)rootInterfaceView didSelectItem:(NSUInteger)itemTag;

@end

RootInterfaceView.m

// remember to synthesize the delegate
-(void)rootInterfaceItemSelected: (RootInterfaceItemView*)rootInterfaceItemView
{
    NSUInteger theTag = rootInterfaceItemView.tag;
    if ([self.delegate respondsToSelector:@selector(rootInterfaceView:didSelectItem:)])
        [self.delegate rootInterfaceView:self didSelectItem:theTag];
}

Alternatively, if the only options from level 2 were either back to root/pop one VC or to push controller 3, then it'd be fine for level 2 to be importing 3 to allow for it's creation.