Question

I’m not exactly sure what’s going on and hope that I can provide enough relevant code to find an answer. I’ve set up my gesture recognizer in my appDelegate.m:

CCScene *scene = [HomeLayer scene];
HomeLayer *layer = (HomeLayer *) [scene.children objectAtIndex:0];

UIPanGestureRecognizer *gestureRecognizer = [[[UIPanGestureRecognizer alloc] initWithTarget:layer action:@selector(handlePanFrom:)] autorelease];
[director_.view addGestureRecognizer:gestureRecognizer];
m._gestureRecognizer = gestureRecognizer;

I’ve inserted some debugging messages to try to pinpoint at what point the app crashes:

- (void)handlePanFrom:(UIPanGestureRecognizer *)recognizer {
    NSLog(@"Handle Pan From");

as well as some printouts for ccTouchBegan/Moved/Ended.

Every time the app crashes, it’s while things are “moving”, (ended never gets called), and handlePanFrom never gets called either.

Background info: My app has buttons that I use to switch between scenes, for example:

- (void) doSomethingThree: (CCMenuItem  *) menuItem
{
    NSLog(@"The third menu was called");
    [[CCDirector sharedDirector] replaceScene:[CCTransitionFade transitionWithDuration:1.0 scene:[HomeLayer scene] ]];
}

If I start up my app and go directly to the HomeLayer scene, and try to drag, the app crashes instantly 100% of the time (ccMoved gets called 1-2 times before crash). Clicking does not cause the app to crash, only anything that would invoke handlePanFrom.

The strange thing is that if I drag around on any other scene, the app does not crash, and handlePanFrom successfully gets called. Then, when I go back to the HomeLayer scene and drag around, it won’t crash for some time, and it seems directly related to how long I spend dragging around on a different scene.

Has anyone seen these symptoms before? I’m not sure if the information I provided is relevant or correct, I’m still trying to learn my way around iphone dev. I’ll also be happy for any debugging tips (those assembly looking hex lines aren’t particularly enlightening to me…)

Answer 1

I figured out the problem with the help of NSZombies, finding out that the program was crashing while trying to reference the deallocated method handlePanFrom.

The ultimate root of the problem was that HomeLayer was being instantiated twice, the first time in appDelegate.m, and the 2nd time when i was doing the replaceScene.

This resulted in the first layer eventually losing all of its references and being deallocated while the gestureRecognizer was still trying to reference [layer handlePanFrom], causing the crash.

The problem was fixed by moving the gestureRecognizer from the appDelegate.m to HomeLayer.m, and for anyone who needs gestures across multiple layers, here’s a piece of code that will remove any existing references of the gestureRecognizer to the view, and then add a new one that targets a method in the layer:

+(CCScene *) scene
{
    HomeLayer *layer = [HomeLayer node];

    [scene addChild: layer];

    for (UIGestureRecognizer *gr in [[CCDirector sharedDirector].view gestureRecognizers]) {
        // note that sharedDirector is a singleton and therefore is the same CCDirector
        // as the one used in appDelegate.m
        [[CCDirector sharedDirector].view removeGestureRecognizer:gr];
    }

    UIPanGestureRecognizer *gestureRecognizer = [[[UIPanGestureRecognizer alloc] initWithTarget:layer action:@selector(handlePanFrom:)] autorelease];

    [[CCDirector sharedDirector].view addGestureRecognizer:gestureRecognizer];

    return scene;
}

Hopefully that may help someone in the future who is trying to work with multiple scenes/layers in a view =)