iPhone: value of selectedIndex for tab should be consistent, but isn't

Question

This should be so simple... but something screwy is happening.

My setup looks like this:

MainViewController
   Tab Bar Controller
      4 tabs, each of which loads WebViewController

My AppDelegate contains an ivar, tabBarController, which is connected to the tab bar controller (this was all set up in Interface Builder). The leftmost tab is marked "selected" in IB.

Within the viewWillAppear method in WebViewController, I need to know which tab was just selected so I can load the correct URL. I do this by switching on appDelegate.tabBarController.selectedIndex.

When the app first runs and the leftmost tab is selected, selectedIndex is a large garbage value. After that, I get values from 0 to 3, which is as it should be, but they are in random order. Not only that, but each tab I touch reports a different value each time.

This app is extremely simple right now and I can't imagine what I could have done to make things go this wrong.

Has anyone seen (and hopefully solved) this behavior?

Update: we have a request for code. There's not much to see.

The tab bar controller gets loaded in applicationDidFinishLaunching:

[self.mainViewController view];  //force nib to load
[self.window addSubview:self.mainViewController.tabBarController.view]

There is currently no code whatsoever in MainViewController.m other than the synthesize and release for tabBarController.

From WebVewController.m:

- (void)viewWillAppear:(BOOL)_animation {
    [super viewWillAppear:_animation];

    NSURL *url;
    switch([S_UIDelegate mainViewController].tabBarController.selectedIndex) {
        case 0: url = [NSURL URLWithString:@"http://www.cnn.com"];
            break;
        case 1: url = [NSURL URLWithString:@"http://www.facebook.com"];
            break;
        case 2: url = [NSURL URLWithString:@"http://www.twitter.com"];
            break;
        case 3: url = [NSURL URLWithString:@"http://www.google.com"];
            break;
        default: url = [NSURL URLWithString:@"http://www.msnbc.com"];
    }

    NSURLRequest *request = [NSURLRequest requestWithURL:url];
    [webView loadRequest:request];
}

This is where I'm seeing the random values. BTW, S_UIDelegate is just a macro that returns a pointer to the app delegate. I'm using someone else's app template and he's a huge fan of #define to save on typing.

Answer 1

You should try to move your switch case into a tabBarController delegate : – tabBarController:shouldSelectViewController: – tabBarController:didSelectViewController:

Answer 2

A co-worker just provided the answer. selectedIndex isn't set up yet in viewWillAppear; when I switched to using viewDidAppear instead, it works as expected.