Crash when trying to present UIActivityViewController

Question

I see a crash in Crashlytics than happens to my users sometimes. The crash happens when presenting UIActivityViewController in the last line of the following code:

NSData* snapShot = ... ;

UIActivityViewController *activityViewController = [[UIActivityViewController alloc] initWithActivityItems:[NSArray arrayWithObjects:activityTextsProvider, snapShot ,nil] applicationActivities:[NSArray arrayWithObjects:customActivityA, customActivityB, customActivityC, nullptr]];

activityViewController.excludedActivityTypes = [NSArray arrayWithObjects:UIActivityTypePrint, UIActivityTypeAssignToContact, UIActivityTypeMail, UIActivityTypeCopyToPasteboard, nil];
activityViewController.popoverPresentationController.sourceView = self.myButton;
activityViewController.popoverPresentationController.sourceRect = self.myButton.bounds;

activityViewController.completionWithItemsHandler = ^(NSString *activityType, BOOL completed, NSArray *returnedItems, NSError *activityError)
{
    ...
};

[self presentViewController:activityViewController animated:YES completion:nil];

I perform this in the main thread and unable to reproduce this crash locally. What could be the reason of this crash?

Edit: I changed nullptr to nil and the issue still happened. I managed to reproduce the issue: the crash happens only if before opening the activity controller i showed a UIMenuController. When creating UIActivityViewController it is not nil, but when presenting the controller i see the crash in the presentViewController line and the activity controller there is shown as nil

What is `nullptr` in the second array? If you want to insert null into an array, try `[NSNull null]`. — József Vesza, May 05 '15 at 08:52
This is a c++ nil. Did not notice i used nullptr there but it should not make any difference — Erik Sapir, May 05 '15 at 08:54
I thought it was worth mentioning, since collection types can't contain nil items (uness it's `[NSNull null]`). — József Vesza, May 05 '15 at 08:55
Damn, you're actually right about that. I got too used to using the `@[item1, item2]` shorthand. :) — József Vesza, May 05 '15 at 09:01
I actually starting to think that this nullptr must be the reason for the crash. Will try to send my users a new version with this change and see if crash reproduces — Erik Sapir, May 05 '15 at 09:15
From this SO post ( http://stackoverflow.com/questions/1564410/when-to-use-nil-and-null-in-objective-c ), "nil and Nil and NULL are identical in Objective-C and in Objective-C++ before C++11" and "nil and Nil and std::nullptr are identical in Objective-C++ with C++11" - may be relevant. You really should just use nil everywhere. — Joshua Nozzi, May 05 '15 at 14:52

score 0 · Answer 1 · answered May 05 '15 at 15:03

József addressed the use of nullptr in comments, and Fogh is spot-on that the actual crash log is important (please edit your question and post the full crash log), but I'd like to point out something else.

You're assuming your call to initialize activityViewController is succeeding. You should code defensively (by assuming everything that can fail probably will fail and testing for this at runtime). Wrap the rest of the configuration and presentation inside an if (activityViewController != nil) {} condition (you should probably have an else with proper error handling/reporting too) so you're properly detecting an all-out initialization failure for multiple reasons (like a misplaced nib, missing resource, etc.).

In your case, I think it's likely the initialization is failing because your class is doing something with a faulty array, as József's nullptr catch suggests. Perhaps you're using one or more pre-C++11 c libraries / compiling with a non-C11/gnu11 "C Language Dialect" build setting and nullptr is not equivalent to nil, leading to strange results in a supposed-to-be-nil-terminated array?

Note: If that turns out to be the case, I'll happily take an upvote but would rather József post his comment as an answer so you can give him proper credit. (Feel free to edit this request out of my answer if/when that happens.)

Edited my question with additional info. There is nothing in the log regarding the crash — Erik Sapir, May 06 '15 at 07:27

Crash when trying to present UIActivityViewController

1 Answers1