ios - ivar is null inside a block, although set before block execution

Question

I have the following code:

[GetUserData getUserDataWithBlock:^(UserData *userData, NSError *error)
              {
                  self.userData = userData;
              #1  self.userData.fbUser = user;
                  // Call REST API of server 'GetAllWords'
                  [GetAllWords getAllWordsWithBlock:^(NSSet *newWords, NSError *error)
                   {
                       [self saveAllWords:newWords];
                   #2  [self showRootView];
                   }];
              }];

The problem is, that self.userData is correctly set in #1 (and is not null), but when I'm getting to #2 - self.userData becomes null... Point #1 is the only place where I set self.userData.

Is GCD involved here? If so, please provide code for that.

Unheilig
– Unheilig

2013-09-23 00:09:19 +00:00
Commented Sep 23, 2013 at 0:09 — Unheilig
– Unheilig, Commented Sep 23, 2013 at 0:09

Community · Accepted Answer · 2020-06-20 09:12:55Z

I could imagine the behavior you describe if the userData property was defined as weak (notably, if getAllWordsWithBlock runs asynchronously).

If not, I'd suggest setting up a "watch" on the underlying variable:

setting a breakpoint at point #1 (and at point #2, presumably) in your code and start the app in the debugger;
when the debugger stops at your first breakpoint, add a watch on the variable that backs your userData property by right-clicking (or control-clicking) on the variable in the "Variables" view and choosing "Watch" (obviously, this screen snapshot is a different piece of code, but it illustrates how to create a "watch" in Xcode):
resuming execution by hitting the continue button:
when you hit a watch breakpoint, sometimes you'll be staring at assembler, but you can hit the "step out" button until you get to a point in your code you recognize.

That can be helpful in identifying what is changing your variable (if not a simple weak property problem).

Collectives™ on Stack Overflow

ios - ivar is null inside a block, although set before block execution

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related