Question

I am trying to solve a larger problem and I am tipping on the fact that ARC apparently is releasing the view to my NSViewController too early. I think 🙂 So I created a simple app to reconstruct the situation.

I have a simple ARC Cocoa application. In the Window of the MainMenu.xib I hook up a Custom View to a @property (strong) IBOutlet NSView *theView; which is declared in the AppDelegate.h

In the AppDelegate.m I synthesize the property and then call the following:

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
    TestViewController *tvc =  [[TestViewController alloc] initWithNibName:@"TestViewController" bundle:nil];
    [_theView addSubview:[tvc view]];
}  

The TestViewControllergets displayed in the Custom View – no problem. It contains one NSButton. It is hooked up to a method called -(IBAction)btnPressed:(id)sender and one NSTextView which is also hooked up as an IBOutlet.

In the TestViewController.h I declare:

@property (nonatomic, strong) IBOutlet NSTextField *textField;
@property (nonatomic, strong) NSString *theString;

-(IBAction)btnPressed:(id)sender;

In the TestViewController.m I then do

@synthesize theString = _theString;
@synthesize textField = _textField;

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Initialization code here.
        _theString = @"Hello World";
    }

    return self;
}

-(IBAction)btnPressed:(id)sender
{
    [_textField setStringValue:_theString];
}

When I run the app and press the button it crashes. If I check it for zombies I receive the following:

#   Address Category    Event Type  RefCt   Timestamp   Size    Responsible Library Responsible Caller
0   0x7f97a3047560  TestViewController  Malloc  1   00:00.652.631   128 TestARC -[AppDelegate applicationDidFinishLaunching:]
1   0x7f97a3047560  TestViewController  Retain  2   00:00.653.088   0   TestARC -[TestViewController initWithNibName:bundle:]
2   0x7f97a3047560  TestViewController  Release 1   00:00.653.089   0   TestARC -[TestViewController initWithNibName:bundle:]
3   0x7f97a3047560  TestViewController  Retain  2   00:00.653.912   0   AppKit  -[NSNib instantiateNibWithOwner:topLevelObjects:]
4   0x7f97a3047560  TestViewController  Release 1   00:00.658.831   0   AppKit  -[NSNib instantiateNibWithOwner:topLevelObjects:]
5   0x7f97a3047560  TestViewController  Release 0   00:00.662.377   0   Foundation  -[NSNotificationCenter postNotificationName:object:userInfo:]
6   0x7f97a3047560  TestViewController  Zombie  -1  00:01.951.377   0   AppKit  -[NSApplication sendAction:to:from:]

What am I doing wrong?
Thanks

Answer 1

Add a property to hold the view controller. Your controller currently has nothing to keep it alive past the end of the method that allocates it.

Add:

@property (strong) TestViewController *tvc;

Modify:

self.tvc =  [[TestViewController alloc] initWithNibName:@"TestViewController" bundle:nil];

(I’m curious…what do you see as the point of creating a view controller if all you want is the view it contains?)

---

Concerning the general approach, it seems that this is more properly behavior that should be implemented using a container view controller. That mechanism allows multiple view controllers to share the screen in an organized way.