how to know if UIButton titlelable.text changed

Question

I just want to know how can I fire some function when button title change ? i tried to use this command but nothing work :

[button addTarget:self 
           action:@selector(function:) 
       forControl:UIControlEventValueChange];

Answer 1

You can use an observer in your viewcontroller that has an outlet to the button:

1. First add the observer (in viewDidLoad for example)

   [self.button addObserver:self 
                 forKeyPath:@"titleLabel.text" 
                    options:NSKeyValueObservingOptionNew 
                    context:NULL];
   

2. Override default observer method on your viewcontroller

   - (void)observeValueForKeyPath:(NSString *)keyPath 
                         ofObject:(id)object 
                           change:(NSDictionary *)change 
                          context:(void *)context {
   
       if ([keyPath isEqualToString:@"titleLabel.text"]) {
           // Value changed
           UIButton *button = object;
           NSString *title = button.titleLabel.text;
       }
   }
   

3. Remove yourself as observer in the dealloc function

   [self.button removeObserver:self forKeyPath:@"titleLabel.text"];