About Hide the keyboard - ios7

Question

My question is :
When I write a user login UI, because the keyboard hide the password textfield, so I write some code to scroll up the login UI, but when the keyboard is hidden and the UI is scrolled to the old position, I find I touch the textfield which I can't get any response.
registe notification:
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(keyboardWillshow:)
name:UIKeyboardWillShowNotification
object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(keyboardWillhide:)
name:UIKeyboardWillHideNotification
object:nil];
_username.delegate = self;
_password.delegate = self;
will show keyboard code:
- (void) keyboardWillshow:(NSNotification *)noti
{
NSDictionary *userInfo = [noti userInfo];
NSValue *keyValue = [userInfo objectForKey:UIKeyboardFrameEndUserInfoKey];
CGRect keyboardRect = [keyValue CGRectValue];
int height = keyboardRect.size.height;
userInfo = nil;
keyValue = nil;
[UIView animateWithDuration:0.5f animations:^{
self.containView.frame = CGRectMake(0, -height+20, WIDTH/2, HEIGHT/2-20);
}];
}
will hide keyboard code:
- (void)keyboardWillhide:(NSNotification *)noti
{
[UIView animateWithDuration:0.5f animations:^{
self.containView.frame = CGRectMake(0, 20, WIDTH/2, HEIGHT/2-20);
}];
}
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
[_password resignFirstResponder];
[_username resignFirstResponder];
}
Could some one help me? I use the storyboard to write the code.