为什么 UITextField 在 resignFirstResponder 上呈现动画？

从 iOS 8 开始，表单中的 UITextField 行为非常奇怪。如果我单击另一个文本字段或按键盘上的 Tab，输入的文本会向上动画然后快速重新出现。每次视图加载后以及之后时不时都会发生这种情况。

它看起来像这样：

我的代码如下所示：

#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:

看起来这个问题是由我的键盘监听器引起的：

[[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];
}

问题似乎是您正在执行以下代码段

-(void)keyboardWillShow:(NSNotification *)sender

即使键盘已经处于活动状态，这也会导致一些失真。

一个小的解决方法是在调整框架之前检查键盘是否已经处于活动状态，如下所示

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;
    }
}