CODEWITHSUNDEEP
iphoneios
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Reputation: 4731

-viewDidUnload is not called after memory warning when xib is not used

When I use xib, -viewDidUnload is called after memory warning.
But when I create view programmatically instead of using xib, -viewDidUnload is not called.

(In both cases, -didReceiveMemoryWarning is called.)

Why -viewDidUnload is not called when I don't use xib file?
Don't I have to write code for -viewDidUnload if I don't use xib?

The followings are the test code and results:
(I'm using ARC)

@implementation ViewControllerA
- (void)viewDidLoad
{
    [super viewDidLoad];

    self.title = [NSString stringWithFormat:@"%d", gNavigationController.viewControllers.count];

    // button to pop view controller to navigation controller
    UIButton *button = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    button.frame = CGRectMake(100, 100, 200, 50);
    [button setTitle:@"push" forState:UIControlStateNormal];
    [button addTarget:self action:@selector(push) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:button];

    // button to generate memory warning
    button = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    button.frame = CGRectMake(100, 200, 200, 50);
    [button setTitle:@"memory warning" forState:UIControlStateNormal];
    [button addTarget:self action:@selector(generateMemoryWarning) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:button];

    NSLog(@"view did load %@", self.title);
}

- (void)generateMemoryWarning {
    [[UIApplication sharedApplication] performSelector:@selector(_performMemoryWarning)];
}

- (void)push {
    UIViewController *viewController = [[ViewControllerA alloc] init];
    [gNavigationController pushViewController:viewController animated:YES];
}

- (void)viewDidUnload
{
    [super viewDidUnload];
    NSLog(@"view did unload %@", self.title);
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    NSLog(@"view did receive memory warning %@", self.title);
}

@end

RESULTS

if ViewControllerA doesn't have xib:

view did load 1
view did load 2
view did receive memory warning 1
view did receive memory warning 2

if ViewControllerA has xib:

view did load 1
view did load 2
view did unload 1
view did receive memory warning 1
view did receive memory warning 2

Upvotes: 3

Views: 772

Answers (1)

Vimal Venugopalan
Vimal Venugopalan

Reputation: 4091

If you are using UIViewContoller without initializing it from a NIB, you need to subclass the -loadView method. Otherwise iOS assumes that the view cannot be unloaded / reloaded.

It would be sufficient to just add the following to your implementation:

- (void)loadView {
    [super loadView];
    self.view = yourCreatedView;
}

Unfortunately the documentation is not very clear on this.

Upvotes: 2

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