How does work viewWillAppear? - objective-c

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.

Answer 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;
}
}

Answer 2

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;
}