Objective-C – Message a view controller from application delegate

Question

I want to download some data in the application delegate in - application:didFinishLaunchingWithOptions:

After I have downloaded some data I want to set this data to an NSArray property in a view controller. If I have a synthesized property of NSArray (nonatomic, retain) called data I would like to do [viewController setData:downloadedData];

How would I call the active viewController instance from the application delegate?

My application structure is a Tab Bar Controller as root controller.

Answer 1

You'll want to use NSNotificationCenter which will essentially broadcast a message to all objects that have subscribed to that particular message.

In your view controller subscribe to the notification:

[[NSNotificationCenter defaultCenter] 
    addObserver:self 
    selector:@selector(downloadedData:) 
    notificationName:@"DownloadedData" 
    object:data];

- downloadedData:(NSNotification *)notification {
    self.data = notification.object;
}

And in your app delegate send the notification to the subscribers:

[[NSNotificationCenter defaultCenter] 
    postNotificationName:@"DownloadedData" 
    object:data];