Why is UITextField animating on resignFirstRespond

问题:

Since iOS 8, UITextFields in a form behave very strangely. If I click an another text field or press Tab on the keyboard, the entered text animates upwards then reappears quickly. It happens every time after the view did loaded, and every now and then afterwards.

It looks like this:

My code looks like this:

#pragma mark - <UITextFieldDelegate>

- (BOOL)textFieldShouldReturn:(UITextField *)textField
{
    if (textField == self.passwordTextField) {
        [self loginButtonClicked:nil];
    } else if (textField == self.emailTextField) {
        [self.passwordTextField becomeFirstResponder];
    }

    return YES;
}

EDIT:

It looks like this issue is caused by my keyboard listeners:

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillHide:) name:UIKeyboardWillHideNotification object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillShow:) name:UIKeyboardWillShowNotification object:nil];


- (void)keyboardWillHide:(NSNotification *)sender
{
    self.loginBoxBottomLayoutConstraint.constant = 0;

    [self.view layoutIfNeeded];
}

- (void)keyboardWillShow:(NSNotification *)sender
{
    CGRect frame = [sender.userInfo[UIKeyboardFrameEndUserInfoKey] CGRectValue];
    CGRect newFrame = [self.view convertRect:frame fromView:[[UIApplication sharedApplication] delegate].window];
    self.loginBoxBottomLayoutConstraint.constant = CGRectGetHeight(newFrame);

    [self.view layoutIfNeeded];
}

回答1:

The problem seems to be that you are executing the piece of code in

-(void)keyboardWillShow:(NSNotification *)sender

even if the keyboard is already active, which leads to some distortion.

A small work around would be to check if the keyboard is already active before adjusting the frames, as below

bool isKeyboardActive = false;

-(void)keyboardWillHide:(NSNotification *)sender

{

    self.boxBottomConstraint.constant = 0;
    [self.view layoutIfNeeded];
    isKeyboardActive = false;
}


-(void)keyboardWillShow:(NSNotification *)sender

{

    if (!isKeyboardActive) {
        CGRect frame = [sender.userInfo[UIKeyboardFrameEndUserInfoKey] CGRectValue];
        CGRect newFrame = [self.view convertRect:frame fromView:[[UIApplication sharedApplication] delegate].window];
        self.boxBottomConstraint.constant = CGRectGetHeight(newFrame);
        [self.view layoutIfNeeded];
        isKeyboardActive = true;
    }
}

回答2:

Try this

 - (void)textFieldDidEndEditing:(UITextField *)textField
 {
    [textField layoutIfNeeded]; 
 }

Which I guess should resolve your issue. Got some similar post at UITextField: When beginning input, textfield bounces up, and then bounces down

IOS8 Text in TextField Bounces on Focus

Let me know if still we have issue

回答3:

Try wrapping your code in this

[UIView performWithoutAnimation:^{
// Changes we don't want animated here
}];