I needed to create an application base with multiple view
controllers, and an easy method for switching between them. I came up
with a solution that passes messages via the App Delegate, and has a
parent View Controller that manages the sub-views.

The following code is the App Delegate:

MultiviewAppDelegate.h

#import 
 
@class MultiviewViewController;
 
@interface MultiviewAppDelegate : NSObject  {
       UIWindow *window;
       MultiviewViewController *viewController;
}
 
@property (nonatomic, retain) IBOutlet UIWindow *window;
@property (nonatomic, retain) IBOutlet MultiviewViewController *viewController;
 
-(void) displayView:(int)intNewView;
 
@end

MultiviewAppDelegate.m

#import "MultiviewAppDelegate.h"
#import "MultiviewViewController.h"
 
@implementation MultiviewAppDelegate
 
@synthesize window;
@synthesize viewController;
 
-(void) displayView:(int)intNewView {
       [viewController displayView:intNewView];
}
 
- (void)applicationDidFinishLaunching:(UIApplication *)application {
       [window addSubview:viewController.view];
       [window makeKeyAndVisible];
}
 
 
- (void)dealloc {
       [viewController release];
       [window release];
       [super dealloc];
}
 
 
@end

Pretty basic stuff (almost exactly the default for the AppDelegate
template). The only addition is the displayView function, which
passes a message to the parent View Controller.

MultiviewViewController.h

#import 
 
@interface MultiviewViewController : UIViewController {
}
 
- (void) displayView:(int)intNewView;
 
@end

This has an internal displayView function which is called by the
AppDelegate.

MultiviewViewController.m

#import "MultiviewViewController.h"
// you have to import the header files for
// any views that this parent controls
#import "View01.h"
#import "View02.h"
 
@implementation MultiviewViewController
 
UIViewController  *currentView;
 
- (void) displayView:(int)intNewView {
       NSLog(@"%i", intNewView);
       [currentView.view removeFromSuperview];
       [currentView release];
       switch (intNewView) {
               case 1:
                       currentView = [[View01 alloc] init];
                       break;
               case 2:
                       currentView = [[View02 alloc] init];
                       break;
       }
 
       [self.view addSubview:currentView.view];
}
 
 
- (void)viewDidLoad {
       // display Welcome screen
       currentView = [[View01 alloc] init];
       [self.view addSubview:currentView.view];
 
   [super viewDidLoad];
}
 
- (void)didReceiveMemoryWarning {
   [super didReceiveMemoryWarning]; // Releases the view if it
doesn't have a superview
   // Release anything that's not essential, such as cached data
}
 
 
- (void)dealloc {
       [currentView release];
   [super dealloc];
}
 
@end

Now we just have to have multiple sub-views.

View01.h

#import 
 
@interface View01 : UIViewController {
 
}
 
@end

View01.m

#import "View01.h"
#import "MultiviewAppDelegate.h"
 
@implementation View01
 
- (void)goToTwo {
       MultiviewAppDelegate *appDelegate = [[UIApplication
sharedApplication] delegate];
       [appDelegate displayView:2];
}
 
- (void)viewDidLoad {
       NSLog(@"load01");
 
       UIButton *btnOne = [UIButton buttonWithType:UIButtonTypeRoundedRect];
       btnOne.frame = CGRectMake(40, 40, 240, 30);
       [btnOne setTitle:@"One!" forState:UIControlStateNormal];
       [btnOne addTarget:self action:@selector(goToTwo)
forControlEvents:UIControlEventTouchUpInside];
       [self.view addSubview:btnOne];
 
   [super viewDidLoad];
}
 
- (void)didReceiveMemoryWarning {
   [super didReceiveMemoryWarning]; // Releases the view if it
doesn't have a superview
   // Release anything that's not essential, such as cached data
}
 
 
- (void)dealloc {
       NSLog(@"dealloc01");
   [super dealloc];
}
 
 
@end

The second view looks just like the first, but goes to “one”
instead of two.

View02.h

#import 
 
@interface View02 : UIViewController {
 
}
 
@end

View02.m

#import "View02.h"
#import "MultiviewAppDelegate.h"
 
@implementation View02
 
- (void)goToOne {
       MultiviewAppDelegate *appDelegate = [[UIApplication
sharedApplication] delegate];
       [appDelegate displayView:1];
}
 
- (void)viewDidLoad {
       NSLog(@"load02");
 
       UIButton *btnTwo = [UIButton buttonWithType:UIButtonTypeRoundedRect];
       btnTwo.frame = CGRectMake(40, 40, 240, 30);
       [btnTwo setTitle:@"Two!" forState:UIControlStateNormal];
       [btnTwo addTarget:self action:@selector(goToOne)
forControlEvents:UIControlEventTouchUpInside];
       [self.view addSubview:btnTwo];
 
   [super viewDidLoad];
}
 
- (void)didReceiveMemoryWarning {
   [super didReceiveMemoryWarning]; // Releases the view if it
doesn't have a superview
   // Release anything that's not essential, such as cached data
}
 
 
- (void)dealloc {
       NSLog(@"dealloc02");
   [super dealloc];
}
 
 
@end

And that’s it! It seems like a lot, but it’s a basic framework that makes it easy to add in new views and navigate between them.

I created this to help me go between multiple screens built by different developers that weren’t working in the same environment. It makes it easy to add the .m and .h file of a View Controller, and then with some minor changes, be able to insert it into the navigation flow of any application.

One caveat: if you have a timer, you need to invalidate it before you call [appDelegate displayview:]. I’ve also been making it a habit to set my objAccelerator.delegate = nil in the dealloc function of each View Controller.

You must also have good memory management practices (release everything you alloc!), because the dealloc is not just called when the program terminates — it’s called every time you switch views.

Download the iphone multiview controller source code here!