Question

I have a three tab application that shares a plist for connection information (Client ID, Server Address, Port Number). In each of the view controllers, an NSUserDefaults object is initialized within the viewDidLoad method:

- (void)viewDidLoad {
    [super viewDidLoad];

    // load default settings into class instance variables
    defaults = [NSUserDefaults standardUserDefaults];
    self.clientID = [defaults objectForKey:@"clientID"];
    self.serverAddress = [defaults objectForKey:@"serverAddress"];
    self.serverPort = [defaults objectForKey:@"serverPort"];
}

One of my views represents a “Settings” page that allows a user to make changes to the plist. However, when the plist is updated, the changes aren’t reflected across all of the tab views because a synchronize is needed for each of the objects:

[defaults synchronize];

I’ve learned that the viewDidLoad method is only called once during the lifetime of an application (at least for a Tab Bar application), so, I can’t put the synchronize calls here. I then turned to the AppDelegate class and discovered the tabBarController method. How do I use this method to synchronize the NSUserDefaults objects across all view controllers without the need for a sync button? Is this even the correct way of sharing/adjusting preferences while an application is open?

Here’s where I’m at now:

- (void)tabBarController:(UITabBarController *)tabBarController didSelectViewController:(UIViewController *)viewController {

    // I need to synchronize somewhere in here???
    switch (tabBarController.selectedIndex)
    {
    case 0:
        NSLog(@"Tab 0 selected");
        break;
    case 1:
        NSLog(@"Tab 1 selected");
        break;
    case 2:
        NSLog(@"Tab 2 Selected");
        break;
    }
}

Thanks ahead of time.

Answer 1

Try syncing the defaults in viewWillAppear instead of viewDidLoad.

It may happen that viewDidLoad is called multiple times (in which case, viewDidUnload will have been called between), for example, if there is a memory issue.

By synchronizing the defaults in viewWillAppear, you are ensuring that the relevant UIViewController is updated just before it becomes the selected view controller.