objective-cmemory-managementnserrornszombieuimanageddocument

-[NSError retain]: message sent to deallocated instance

With Zombies enabled, I'm getting the error in the title (message sent to deallocated instance of NSError) on the following saveToURL call:

[aDocument saveToURL:aDocument.fileURL
forSaveOperation:UIDocumentSaveForOverwriting
completionHandler:^(BOOL success) { ...

Stack trace looks like the following:

enter image description here

aDocument is an instance of a subclass of UIManagedDocument. I have concurrency debug on and I've looked to see if I have any threading conflicts, haven't been able to find any yet. How can I debug this?

EDIT: Also tried the following code with the same crash occurring

__weak typeof(self) weakSelf = self;

    [aDocument saveToURL:aDocument.fileURL forSaveOperation:UIDocumentSaveForOverwriting completionHandler:^(BOOL success) {
        if (success) {
            dispatch_async(dispatch_get_main_queue(), ^{
                [weakSelf documentSaved:aDocument forRestoredAssessment:patientAssessment];
            });
        }
    }];

EDIT: bounty added

Solution

  • I believe I figured out what was causing this, since I made the following change and then the error went away. The error was tricky to resolve though since it did not directly point to this being the cause.

    I was using UIDocumentSaveForOverwriting but I discovered that sometimes the file had already been deleted by another process.

    So to fix the issue I tested for file existence and then used either UIDocumentSaveForOverwriting or UIDocumentSaveForCreating based on that.