如何限制文本框輸入的個數

- (void)viewDidLoad {
    [super viewDidLoad];
    UITextField *textF = [[UITextField alloc]initWithFrame:CGRectMake(100, 100, 100, 100)];
    textF.backgroundColor = [UIColor grayColor];
    [self.view addSubview:textF];
    self.textF = textF;
    
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(limitTextField:) name:@"UITextFieldTextDidChangeNotification" object:textF];


}


- (void)limitTextField:(NSNotification *)note {
    int limit = 5;
    if ([self.textF.text length] > limit) {
        [self.textF setText:[self.textF.text substringToIndex:limit]];
    }
}


-(void)dealloc{
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}