prepareForSegue is not called after performSegue:withIdentifier: with popover style

Question

I have a universal app, where I am sharing the same controller for a IPad and IPhone storyboard. I have put a UILongPressGestureRecognizer on a UITableView, that when a cell is pressed on iPhone it calls an action that perform a segue:

-(IBAction)showDetail:(id)sender {
    UILongPressGestureRecognizer *gesture = (UILongPressGestureRecognizer*)sender;
    if (gesture.state == UIGestureRecognizerStateBegan) {
        CGPoint p = [gesture locationInView:self.theTableView];

        NSIndexPath *indexPath = [self.theTableView indexPathForRowAtPoint:p];
        if (indexPath != nil) {
            [self performSegueWithIdentifier:SEGUE_DETAIL sender:indexPath];
        }
    }
}

the segue is a detail view performed as a 'push'. The first thing you should notice is that the sender is an NSIndexPath, is the only way I found for passing the selected cell. Maybe there's a better solution. Everything works fine, in a sense that the segue is performed, and before the prepareForSegue is called too.

However it happens that on iPad, I have changed the segue identifier to Popover. Now things are working in part, the segue is performed, but prepareForSegue is not called and therefore the destination view controller is not set up as it should be.

What am I doing wrong ?

Solution 1

What I have discovered so far, is that with any segue identifier that is not popover these are the invocations made by iOS:

• prepareForSegue (on source controller)
• viewDidLoad (on destination controller)

while in popover segue the invocation order is:

• viewDidLoad (on destination controller)
• prepareForSegue (on source controller)

just because I put all my logic in viewDidLoad, the controller was not properly initialized, and a crash happened. So this is not exactly true that prepareForSegue is not called, the truth is that I was getting an exception, and I wrongly mistaken as prepareForSegue not getting called.

I couldn't put everything in viewWillAppear because a call to CoreData had to be made and I didn't want to check if entities were ok each time the view display.

How did I solve this ? I created another method in destination controller

-(void)prepareViewController {
  // initialization logic...
}

and changing the prepareForSegue method in source controller itself:

-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
  MyViewController *mvc = (MyViewController*)[segue destinationViewController];
  // passing variable 
  // with segue style other than popover this called first than viewDidLoad
  mvc.myProp1=@"prop1"; 
  mvc.myProp2=@"prop2";

  // viewWillAppear is not yet called
  // so by sending message to controller
  // the view is initialized
  [mvc prepareViewController];

}

don't know if this is expected behavior with popover, anyway now things are working.

Solution 2

I've noticed that the boiler plate code for Xcode's Master-Detail template (iPhone) uses the following pattern for configuring the detail VC's view:

1. the detail VC's setters (for properties) are overwritten in order to invoke the configureView method (configureView would update all your controls in the view, e.g., labels, etc.)
2. the detail VC's viewDidLoad method also invokes the configureView method

I did not follow this pattern the other day when I was trying to re-use a detail VC in my movie app, and this gave me trouble.

I don't have much experience with popovers; however, if the pattern above is used with a detail VC that is displayed inside a popover, then wouldn't the detail VC's view get configured when you set the detail VC's properties from within the prepareForSegue method?

Comments

[GeoffCoope]

Your fix worked for me too so thanks but this is a strange issue as it only just cropped up for me even though I have several other pop overs that work fine and rely on prepareForSegue to forward on objects.

[Guy Moreillon]

Same here, sometimes prepareForSegue is called before viewDidLoad, sometimes after... Thanks for the fix.

[gklka]

I think prepareForSegue is called after viewDidLoad when the segue is invoked from the Storyboard, and it is the other way if you trigger it manually using -performSegueWithIdentifier:.