CODEWITHSUNDEEP
iosobjective-cdelegates
Teja Nandamuri
Teja Nandamuri

Reputation: 11201

How to set delegate for case: Message sent to deallocated instance

When I login, I call the VC2 by segue from VC1

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender{
    if ([[segue identifier] isEqualToString: @"embeddedVC2"]) {
        self.VC2 = [segue destinationViewController];
        self.VC2.delegate = self;
    }
  }

and I have the dealloc in VC1

 -(void)dealloc{
   self.VC2.delegate=nil;
}

The delegate in VC2 is declared as (nonatomic,assign)

and in VC2, I'm performing a download operation, and when it finishes I'm calling

  [self.delegate downloadFinish:self.downloadData];

The problem is that by the time the download is finsihed, the dealloc in VC1 gets called , and its making the delegate in VC2 nil. So the delegate is nil, and [self.delegate downloadFinish:self.downloadData]; doesnt work.

If I remove the self.VC2.delegate=nil in the VC1 dealloc method, then I get the exception at the line:

   [self.delegate downloadFinish:self.downloadData];

message sent to deallocated instance : as VC1 is deallocated and I can't do anything on it.

What is the proper way of handling this scenario ?

Note: This only happens when I redo the procedure again.

Case 1 : login -> VC1 ->VC2 works fine, delegate notifies me about the download finish

Case 2 :no dealloc method in VC1:

login -> VC1 -> VC2 -> logout ->login -> VC1 -> VC2 (boom) crash-message sent to deallocated instance

Case 3 :with dealloc in VC1 and self.VC2.delegate=nil in it:

login -> VC1 -> VC2 -> logout ->login -> VC1 -> VC2 nothing happens,as delegate is set to nil

I tried using Zombie instrument, but I didnt understand a bit. I was confused by the long stack trace and was lost looking at the reference count and retain count numbers. I can post the stacktract in the instruments if you need.

Edit:

I changed the delegate to nonatomic and weak and removed the dealloc methods.

and when I load VC2 by segue , the VC2 delegate is not nil in viewDidLoad, but it turned to be nil by the point the download is finished, and at this point I'm still in VC2. I wonder what is making the delegate nil as I didn't move to another VC.

Upvotes: 0

Views: 147

Answers (1)

mskw
mskw

Reputation: 10328

Make sure you either push a VC, present a VC, or add as a childViewController, this way the parent doesn't get deallocated. Otherwise if you are using tabbar for example, you need to make sure VC1 never gets set to nil.

I would rewrite the way you are adding VC's to your hierarchy if you are spending too much time trying to solve it.

Upvotes: 2

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