Crash when using gesture recognizers in StoryBoard

Question

UPDATE

This is an old question for an old version of Xcode. It turned out that the issue was a bug in Xcode which has been fixed.

Or

Answer 1

The error message tells us that the program is sending the setView: message to an instance of __NSCFString (which is obviously the private implementation class of NSString).

Make sure you have tried running with zombies enabled. A zombie can easily cause an unrecognized selector error.

If it's not a zombie, put a breakpoint on -[NSObject doesNotRecognizeSelector:]. When the breakpoint is hit, you may be able to figure out the problem just from the stack trace. If not, you can print the debugDescription of the object (which is the same as the description for most classes).

On the simulator, you can ask the debugger to print the object's debugDescription like this:

(gdb) frame 0
#0  0x013bcbff in -[NSObject doesNotRecognizeSelector:] ()
(gdb) po ((int*)$ebp)[2]
this is my test string

On the device, you do this:

(gdb) frame 0
#0  0x344bca22 in -[NSObject doesNotRecognizeSelector:] ()
(gdb) po $r0
this is my test string

Update

Based on your steps to reproduce, this is a bug in UIKit. File a bug report. You can work around the bug by creating a strong outlet on SecondViewController and connecting it to the gesture recognizer. Make sure you set the outlet to nil in viewDidUnload.

Update

Do not ever set your outlet to nil -- part of the bug is that UIKit isn't retaining -- you need to keep your reference to make sure that the recognizers aren't released.

Answer 2

In my case, when auto-creating the IBOutlet for the gesture recognizer by drag-n-dropping in the code, Xcode correctly created the property with a "strong" attribute, but it also added the "set to nil" in viewDidUnload. Removing the "set to nil" solved the issue for me.