事件监听

1.监听UITextField输入
- (void)viewDidLoad
{
    [super viewDidLoad];
    
    
    //监听文本输入框的改变
    //1.拿到通知中心
    NSNotificationCenter *center = [NSNotificationCenter defaultCenter];
    
    //2.注册监听：注意一定要写上通知的发布者
    [center addObserver:self selector:@selector(beginEditing) name:UITextFieldTextDidBeginEditingNotification object:self.textField];
    
    [center addObserver:self selector:@selector(textChange) name:UITextFieldTextDidChangeNotification object:self.textField];
    
    [center addObserver:self selector:@selector(endEditing) name:UITextFieldTextDidEndEditingNotification object:self.textField];
}

-(void)beginEditing
{
    NSLog(@"beginEditing");
}

-(void)textChange
{
    NSLog(@"editing.....");
}

-(void)endEditing
{
    NSLog(@"endEditing");
}