How does work viewWillAppear?

Question

My viewWillAppear method call "-(void)doSomething".

- (void)doSomething
{
    Y4AppDelegate * delegate = (Y4AppDelegate *)[[UIApplication sharedApplication] delegate];
    if(delegate.booSomeValue == 0) {
        UIButton * aButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
        [aButton setFrame:CGRectMake(20,360,280,40)];
        [aButton setTitle:@"Title"
                 forState:UIControlStateNormal];
        [aButton addTarget:self
                    action:@selector(mySelector)
          forControlEvents:UIControlEventTouchDown];
        [self.view addSubview:aButton];
    }
}

It work, but aButton is still visible. What can I do to hide aButton? I have three UIViewController. In third i set delegate.booSomeValue to true. When I come back to previous UIViewController, I call this viewWillAppear but aButton is visible. I want to hide it.

score 1 · Accepted Answer · answered Jan 25 '13 at 14:43

1

The problem is that you added it once, and when you go back to it, you are not adding a second one, but the first one you added is still there, so you have to remove it.

To do so, you will need first to create a property to store the button, and check if it exists

if ( ... show button condition ... ) {

    if (!aButton) {
        ... create and show button ...
    }
}
else {
    if (aButton) {
         [aButton removeFromSuperview];
         aButton = nil;
    }
}

answered Jan 25 '13 at 14:43

Ismael

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Thank you for the suggestion fo creating a property. I am new to Objective-C. It's still difficult for me thinking in Objective-C. I came from php. Thank you again. – sensorario Jan 25 '13 at 14:58

score 1 · Answer 2 · answered Jan 25 '13 at 14:48

Move this code to viewDidLoad

- (void)viewDidLoad {
    [super viewDidLoad]
    UIButton * aButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    aButton.tag = 101;
    [aButton setFrame:CGRectMake(20,360,280,40)];
    [aButton setTitle:@"Title"
             forState:UIControlStateNormal];
    [aButton addTarget:self
                action:@selector(mySelector)
      forControlEvents:UIControlEventTouchDown];
    [self.view addSubview:aButton];
}

And

- (void)doSomething
{
    Y4AppDelegate * delegate = (Y4AppDelegate *)[[UIApplication sharedApplication] delegate];
    UIButton * aButton =  (UIButton*)[self.view viewWithTag:101]; 
    aButton.hidden = delegate.booSomeValue;
}

Good answer. I prefer Ismael's solution. He gave answer of my question and you gave me another solution. Thank you. Both answer are useful for me. =( stackoverflow give me the possibility to accept just one as right answer. Sorry. — sensorario, Jan 25 '13 at 14:57
@SimoneDemoGentili It's all right. I'm happy with your upvote :) — Inder Kumar Rathore, Jan 25 '13 at 14:58

How does work viewWillAppear?

2 Answers2