Initialising a ViewController before Segue

Question

I am performing a segue to a view controller that requires an initialisation process. At present the initialisation happens in ViewDidLoad of the target view controller. However the initialisation is fairly lengthy and I would like to show a spinner while it is happening.

If I create a UIActivityIndicatorView within ViewDidLoad and run the initialisation on another thread, of course ViewDidLoad exits and the rest of the loading process happens - in particular shouldAutorotate is called, and this contains code that assumes the initialisation process has occurred. (Even if it didn't, I do not want to show the target view before it has been initialised.)

The answer seems to be to initialise the target view controller before calling the segue. However I can't do that in prepareForSegue in the calling view controller, for the same reason - it exits and the segue is called before the initialisation has happened.

So I seem to need to instantiate the target controller, initialise it and then perform the segue with the initialised controller as the destination. My problem is that I don't know how to do that. The only possible way I have come across is to subclass UIStoryboardSegue and put the initialisation in the init for the subclass. Then I presume I call

UIStoryboardSegue * segue = [[SubclassedSegue alloc]initWithIdentifier:@"??what should this be??" source:self destination:targetViewContoller];
[segue perform];    // which just calls [super perform];

from the source view controller. Is this correct? Can anyone please show me some example code that uses this process - or preferably a simpler way that I haven't thought of? I can't help thinking there must be an easier way to show a spinner.

Thank you for your help.

Answer 1

Segues should be subclassed only when you need to show custom animation/transition during the segue.

In usual scenario, you would want to do this:

__ block Destination *destinationVC = [self.storyboard instantiateViewControllerWithIdentifier:@"destination "];

    //START BUSY CURSOR HERE
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), 
    ^{
        // init whatever you want for destinationVC HERE.
        dispatch_async(dispatch_get_main_queue(), 
      ^{
        //STOP BUSY CURSOR 
       //PERFORM UI UPDATE HERE
       [self presentViewController:destinationVC animated:YES completion:nil];
    });