Hard to fix Zombie

[nobre84]

Hi all... I'm working on an iPad (universal) app that is giving me some trouble. We have a kind of "floating" window that has a close button on the side. Its contents are gathered from a UIViewController instance that have a couple UITextFields on a tableview. The issue comes up when doing multiple touches around on the screen, and the user happens to close the Window during some delegate calls that sometimes get delayed by the system (tableview datasource and delegate calls, textfield delegate calls).
Most of the issues went away when I carefully set the delegates and datasources to nil on the view controller's dealloc method. But one of them persists: if I try to close the window and simultaneously try to begin editing a text field, I get a message sent to deallocated instance

*** -[ViewController respondsToSelector:]: message sent to deallocated instance 0x4240ba0

And this is the call stack :

#0  0x34d4f910 in ___forwarding___ ()
#1  0x34d4f860 in __forwarding_prep_0___ ()
#2  0x300d6ae4 in -[UITextField canBecomeFirstResponder] ()
#3  0x30032ce8 in -[UIResponder becomeFirstResponder] ()
#4  0x300d69cc in -[UITextInteractionAssistant setFirstResponderIfNecessary] ()
#5  0x300d642c in -[UITextInteractionAssistant oneFingerTap:] ()
#6  0x34d44bbe in -[NSObject(NSObject) performSelector:withObject:] ()
#7  0x300c63d2 in -[UIGestureRecognizer _updateGestureWithEvent:] ()
#8  0x300c618a in -[UIGestureRecognizer _delayedUpdateGesture] ()
#9  0x3002d7b0 in _UIGestureRecognizerUpdateObserver ()
#10 0x300451de in _UIGestureRecognizerUpdateGesturesFromSendEvent ()
#11 0x30044fe0 in -[UIWindow _sendGesturesForEvent:] ()
#12 0x30044c0a in -[UIWindow sendEvent:] ()
#13 0x3002ffc6 in -[UIApplication sendEvent:] ()

It seems the system is trying to make the field become first responder, but while it does its thing my dealloc method is reached and the field itself is gone.

Any clue as to what can be done to avoid this ?
It happens when I touch the close button slightly before touching the textField. If I do the opposite, it won't crash.

Thank you
Rafael

[Meredi86]

Hmm im not sure what i would do with that.

From what you have suggested it would require the user to push 2 "buttons" (term used lightly) at the same time - in this case the edit and close buttons?

Couldnt you just move them further apart so that the user would struggle to push them both at the same time? Or as soon as the close button is touched have it lock out the rest of the UI so that nothing on that view can be used until it is reloaded. that way once the close has been pushed the user cant push anything else to cause the exception.

Doesnt really get rid of the problem, but should get around it.

Not elegant but my 2 cents :P

p.s. i know not a push - a Touch

[nobre84]

Thanks for the tip, I'll give it a try setting userInteractions disabled for the content view when tapping the close button, I don't know if it will react fast enough to prevent tho.

[MatthewD]

Could you show some code?

Sounds like if you were to nil your pointer after releasing it, you wouldn't have the crash.

[nobre84]

I had this on the VIew Controller's dealloc, that holds a tableView with a UITextField on each of its cells:

[tableView release];

As "self" was the delegate for the textfields, closing the container window while doing something on the fields (or scrolling the table) had they call a method on the now dead controller
I added these :

//table
    tableView.delegate = nil;
    tableView.dataSource = nil;
//active textfield
if ([currentControl respondsToSelector:@selector(setDelegate:)]) {
        [currentControl setDelegate:nil];
}

This solved the problem for the table and any in-editing text field, but not when activating a previously untouched text field. (only the active text field is having its delegate set to nil).
I then changed the approach, setting the textField delegates to nil on the custom UITableViewCell dealloc method, thus all textfields now have a nil delegate when the Parent view controller is released, but its still crashing :/

Trying to block interactions when clicking the close button didn't work when dealing with multiple, almost instantaneous touches

[nobre84]

The tableviewcell's dealloc is too late to set the delegates to nil, I tried a couple logs in there and the View controller is long gone when the system cleans up the cells, its dealloc is reached by a long stack starting with "delayedPerformCleanup ()" that goes reclaiming all UIViews and removing each one from its superviews.
I'll try to hold pointers to each of them on a collection and do this cleanup straight from the VC's dealloc.