Crash when using gesture recognizers in StoryBoard

Asked 27/1, 2012 at 15:35 Answered 21/6, 2012 at 12:2

Solved iphone objective-c ios interface-builder xcode-storyboard

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.

Original

I have a storyboard generated from making a new tab iphone application (with ARC)

In one of my tabs, if I drag a gesture recognizer (any, but let's say Pan) onto a control, and then set the selector to an action, it just crashes as soon as I go to the tab.

There is nothing in the Console -- it appears to be happening while the storyboard is being loaded (viewDidLoad is never called).

I can't figure out how to get more information
On a different tab, this works fine. Both tabs were generated automatically.

(it's possible I messed something up in the view, but I don't have a clue to figuring out what I did).

If I make gestures programmatically, they work fine, but it's nice to have it work in the storyboard, and I'm afraid that whatever is wrong will cause a crash some other way at some point.

MORE INFO

In the simulator I get

-[__NSCFString setView:]: unrecognized selector sent to instance 0x6d2db70

Again, need debugging techniques -- for example, is there a way to find out what object 0x6d2db70 is?

Which is exactly like this question (with no answer):

Gesture recognizer in Interface builder crashes my app

MORE INFO

This is trivial to reproduce

New iPhone tabbed application, ARC and Storyboard on
Drag tap gesture onto second tab's view (works on first one)
Create an (IBAction)
Connect the gesture's selector connection to the action from #3
run, go to second tab

Crashes. Same thing with my app, default tab works, other tabs don't

Parik answered 27/1, 2012 at 15:35 Comment(10)

What kind of crash? SIGABRT? EXC_BAD_ACCESS? What's the stack trace? – Atomy 27/1, 2012 at 15:38

That's the thing -- console has nothing. Stack trace is back at main in the release pool (so it feels like memory corruption). Need ideas for getting more info. – Parik 27/1, 2012 at 15:59

I have done a LOT of iPhone debugging, but new to 4.2, ARC, etc. I would like ideas for new techniques (I know about zombies, debug malloc, etc -- but they don't seem appropriate). – Parik 27/1, 2012 at 16:0

Also, is there a connection that I need to make besides selector? Does it connect to an IBAction with (id) sender? I can't seem to find any good docs on this. – Parik 27/1, 2012 at 16:1

The action method signatures are documented here. The method can take a sender parameter or not. – Atomy 27/1, 2012 at 16:8

A stack trace pointing at main usually indicates that an exception was thrown. Do you have an exception breakpoint set? – Atomy 27/1, 2012 at 16:8

Besides setting the recognizer's target and action, it needs to be in at least one view's gestureRecognizers outlet collection. You do that by dropping the recognizer on a view. But it should be harmless if it's not in any gestureRecognizers collections. – Atomy 27/1, 2012 at 16:10

Not near my computer right now -- will check all of this when I get to it -- thanks. @rob, add an answer -- I think you've given me enough to solve -- I will edit it with the results. Thanks. – Parik 27/1, 2012 at 17:27

It's trivial to reproduce -- I think it's a bug – Parik 28/1, 2012 at 20:30

Check that the target of the Gesture Recognizer is not deallocated – Industrial 2/6, 2015 at 7:8

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.

Atomy answered 28/1, 2012 at 19:4 Comment(12)

turning on zombies says the tap gesture is a zombie. -[UITapGestureRecognizer retain]: message sent to deallocated instance 0x6b5ba80 – Parik 28/1, 2012 at 19:55

I just noticed that UIImageView doesn't have a gestureRecognizers collection -- I have other UIImageView's where gestures work (also has the IB warning in the inspector). – Parik 28/1, 2012 at 19:57

The gestureRecognizers property is part of UIView, so UIImageView inherits it. It is not tagged IBOutletCollection, so it only shows up in IB if you drop a recognizer on a view. – Atomy 28/1, 2012 at 20:20

Do you have any unsafe_unretained outlets or variables? – Atomy 28/1, 2012 at 20:22

Or any assign properties? Under ARC, assign is the same as unsafe_unretained. – Atomy 28/1, 2012 at 20:23

It's trivial to reproduce -- I think it's a bug (see updated question) – Parik 28/1, 2012 at 20:30

Everything is strong -- I have a trivial project that repros it. No outlets or any variables – Parik 28/1, 2012 at 20:38

That's exactly what I did -- glad that you agree. I am using ARC -- do I need to set the outlet to nil? – Parik 28/1, 2012 at 22:14

This was assigned Problem ID: 10771117 by Apple -- I will update this question if I hear that it was fixed – Parik 28/1, 2012 at 22:22

You need to set the outlet to nil in viewDidUnload. Otherwise it won't get released on a memory warning. – Atomy 28/1, 2012 at 23:43

Unfortunately, you cannot release in viewDidUnload -- when the memory warning comes, the app will crash because UIKit isn't keeping a retain -- you have to hold yours (you can see this by setting to nil in viewDidUpload and simulating a memory warning -- you will crash when you change tabs with a zombie warning) – Parik 31/1, 2012 at 18:52

Wow! I have been experiencing this issue as well, and it wasn't until I reviewed the Device Log in Organizer and found the doesNotRecognizeSelector was caused by the swipe that I managed to find this page. I have the same issue, and the fix above worked (just ctrl+drag the swipe gesture on to the header file of the backing view controller and make it a Strong Outlet - problem solved). Thanks! – Mcclenaghan 27/3, 2012 at 3:55

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.

Microspore answered 21/6, 2012 at 12:2 Comment(1)

That makes sense -- I ran into the same thing after I manually added in the IBOutlet in the standard way. – Parik 21/6, 2012 at 18:15

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