pushViewController debugging

Question

I am trying (from my 3rd child in the heirachy) to load the root view with the following. This does not work and I get the following error when the below code is run.

-[DetailViewController clickButton:]: unrecognized selector sent to instance 0x1161e00'

Code:

 MapViewController *dvController = [[MapViewController alloc] initWithNibName:@"MapView" bundle:[NSBundle mainBundle]];
        [self.navigationController pushViewController:dvController animated:YES];
        [dvController release];
        dvController = nil;

This exact same code works on other views, any idea how to debug this.

Answer 1

The code you wrote to create the MapViewController and push it onto the view controller stack is correct.

The unrecognized selector error is telling you that you are sending are attempting to call a method (named clickButton:) that does not exist.

I would suspect a spelling error. I take it that you most likely have a button defined that calls the code to create the new view. The method should look like this:

-(void) clickButton: (id) sender {
    MapViewController *dvController = [[MapViewController alloc] initWithNibName:@"MapView"  bundle:[NSBundle mainBundle]];
    [self.navigationController pushViewController:dvController animated:YES];
    [dvController release];
    dvController = nil;
}

I would check that you have the ":(id) sender" part. I have made the mistake before of implementing a -(void) clickButton {} method, but had the message actually sending a parameter as well.

Answer 2

1. If you have created the button programatically and set the target as clickButton, make sure the clickButton method is present

2. The clickButton method (according to the error) should take in an argument. So the definition of the method will be

   • (IBAction)clickButton:(id)sender;

3. If you have mapped the IBAction to an event in IB, you can omit the :(id)sender part

4. To load the root view controller from any view in a navigation-based application, use

   [[self navigationController:popToRootViewControllerAnimated:YES];

Answer 3

Sometimes gdb command "backtrace" could help to find a cause of this error. You have to enter this commmand as "bt" on "backtrace" just after an application crash to print out stack. In my case I had a problem that AVPlayer notification was sent to already deallocated instance , because user selected sound and closed view before sound was played completely , so notification was sent to already deallocated object. Backtrace gave me a clue:

#0  0x34c2c118 in ___forwarding___ ()
#1  0x34bbbc50 in __forwarding_prep_0___ ()
#2  0x33c1163c in -[AVAudioPlayer(AVAudioPlayerPriv) finishedPlaying] ()
#3  0x34bb15c0 in -[NSObject(NSObject) performSelector:withObject:] ()
#4  0x3528431c in __NSThreadPerformPerform ()
#5  0x34bfd294 in __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ ()
#6  0x34bff0e2 in __CFRunLoopDoSources0 ()
#7  0x34c00058 in __CFRunLoopRun ()
#8  0x34ba70c2 in CFRunLoopRunSpecific ()
#9  0x34ba6fd0 in CFRunLoopRunInMode ()
#10 0x3033bf90 in GSEventRunModal ()
#11 0x31213b48 in -[UIApplication _run] ()
#12 0x31211fc0 in UIApplicationMain ()
#13 0x000022e0 in main (argc=1, argv=0x2ffff5e8) at /Users/guntis/Projects/MT/MT/main.m:16

Guntis Liepins