UITextField resignFirstResponder无法正常工作？

// Implement viewDidLoad to do additional setup after loading the view, typically from a nib.
- (void)viewDidLoad {
    self.view.backgroundColor = [[UIColor alloc] initWithPatternImage:[UIImage imageNamed:@"iphone_bg_login.png"]];
    self.title = @"Login screen";
    loginTxt = [[UITextField alloc] init];
    pwdText = [[UITextField alloc] init];
    loginFailedTxt = [[UILabel alloc] init];
    loginBtn = [[UIButton alloc] init];
    navAppDelegate = (NavAppDelegate *)[[UIApplication sharedApplication] delegate]; 
    navAppDelegate.navController.navigationBarHidden = YES;
    //NSArray *subVs = (NSArray *) [self.view subviews];
    [super viewDidLoad];
}

UIView (UIControl)

UIControl's touchDown

backgroundTap

-(IBAction) backgroundTap:(id) sender {
    [loginTxt resignFirstResponder];
    [pwdText resignFirstResponder];
    //[[UIApplication sharedApplication] becomeFirstResponder];
        //[sender resignFirstResponder];
}