ios - 如何在 ios 运行时禁用约束？

Question

我有一个进一步有一些文本字段的 View 。我已经用 self 及其 super View 设置了 View 的纵横比。现在，当我单击文本字段然后出现键盘时，我正在调整 View 大小并设置其 y 位置，以便键盘不会覆盖文本字段。我为此使用下面的代码。

- (void)textFieldDidBeginEditing:(UITextField *)textField
{
    /* keyboard is visible, move views */
    if([textField isEqual:self.txt_twitter] || [textField isEqual:self.txt_linkedin])
    {
        [UIView animateWithDuration:0.1f animations:^
         {
             CGRect rect = self.view.frame;

             // 1. move the view's origin up so that the text field that will be hidden come above the keyboard
             // 2. increase the size of the view so that the area behind the keyboard is covered up.
             rect.origin.y -= 130;
            rect.size.height += 130;
             self.view.frame = rect;



         }];
    }

}

- (void)textFieldDidEndEditing:(UITextField *)textField
{

    /* resign first responder, hide keyboard, move views */
    /* keyboard is visible, move views */
    if([textField isEqual:self.txt_twitter] || [textField isEqual:self.txt_linkedin])
    {
        [UIView animateWithDuration:0.1f animations:^
         {
             CGRect rect = self.view.frame;

             // revert back to the normal state.
             rect.origin.y += 130;
             rect.size.height -= 130;


             self.view.frame = rect;


         }];

    }

}

现在，当我的 View 高度增加时，它的宽度也会增加，因为我已经为此设置了约束。请告诉我如何解决这个问题。在这种情况下，我不想增加 View 的宽度。

Answer 1

混合自动布局约束和直接帧操作通常是一个坏主意，您可能应该避免这种情况。我建议您为要移动/调整大小的 View 的高度或位置约束制作一些 IBOutlets，并在委托(delegate)回调中更改 constraint.constant 而不是更改帧。

此外，在处理键盘事件时，最好收听键盘通知(UIKeyboardWillShowNotification)，而不是使用文本字段委托(delegate)方法。

添加了一个 gif 以更好地说明 -



项目中的一些代码:

- (void)viewDidLoad {
    [super viewDidLoad];

    [self addKeyboardNotificationsObserver];
    // Do any additional setup after loading the view, typically from a nib.
}

- (void)addKeyboardNotificationsObserver {

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

}

- (void)handleKeyboardWillShow:(NSNotification *)paramNotification

{

    NSDictionary* info = [paramNotification userInfo];

    //when switching languages keyboard might change its height (emoji keyboard is higher than most keyboards).
    //You can get both sizes of the previous keyboard and the new one from info dictionary.

    // size of the keyb that is about to disappear
    __unused CGSize kbSize = [[info objectForKey:UIKeyboardFrameBeginUserInfoKey] CGRectValue].size;

    // size of the keyb that is about to appear
    CGSize kbSizeNew = [[info objectForKey:UIKeyboardFrameEndUserInfoKey] CGRectValue].size;

    //make adjustments to constraints here...

    self.redSquareBottomConstraint.constant = kbSizeNew.height;

    //and this is where magic happens!

    [self.view layoutIfNeeded];

}

- (void)handleKeyboardWillHide:(NSNotification *)paramNotification

{
    //adjust constraints

    self.redSquareBottomConstraint.constant = 0;

    [self.view layoutIfNeeded];

}

- (void)dealloc {

    [[NSNotificationCenter defaultCenter] removeObserver:self];

}

从代码中可以看出，我们从通知附带的 userInfo 字典中提取键盘的大小。正如 所指出的那样恩格里夫 ，您可以从中提取一些其他有值(value)的信息，例如键盘出现/消散时动画的持续时间(key - UIKeyboardAnimationDurationUserInfoKey)或曲线(key - UIKeyboardAnimationCurveUserInfoKey)。文档 here .如果您想要特定的动画行为，您可以将布局调用包装在动画 block 中，如下所示:

[UIView animateWithDuration:duration
                 animations:^{

    [self.view layoutIfNeeded];

}];