没有使用自动布局的 LayoutConstraints 错误

Question

我没有在我的故事板中使用自动布局，也没有为此实现任何代码。我有一个UIAlertController 用于用户登录，并在键盘文本输入过程中收到LayoutConstraints 错误。

重要的是要注意，当我在 iPad 等实际设备上运行应用程序时不会发生此错误，只会在模拟器中发生。

我正在使用 Xcode 版本 10.1 (10B61) 并在 Debug 中放置了一个 UIViewAlertForUnsatisfiableConstraints 断点，它指示了许多约束错误。

单步执行所有断点后，我在控制台中收到此消息：

[LayoutConstraints] Unable to simultaneously satisfy constraints.
    Probably at least one of the constraints in the following list is one you don't want. 
    Try this: 
        (1) look at each constraint and try to figure out which you don't expect; 
        (2) find the code that added the unwanted constraint or constraints and fix it. 
    (Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints) 
(
    "<NSAutoresizingMaskLayoutConstraint:0x60000165fe80 h=--& v=--& UIKeyboardAssistantBar:0x7f922cd1aa30.height == 0   (active)>",
    "<NSLayoutConstraint:0x6000016768f0 V:|-(0)-[_UIButtonBarStackView:0x7f922cd1d6e0]   (active, names: '|':UIKeyboardAssistantBar:0x7f922cd1aa30 )>",
    "<NSLayoutConstraint:0x600001676a80 V:[_UIButtonBarStackView:0x7f922cd1d6e0]-(0)-|   (active, names: '|':UIKeyboardAssistantBar:0x7f922cd1aa30 )>",
    "<NSLayoutConstraint:0x60000165f340 'UIButtonBar.maximumAlignmentSize' _UIButtonBarButton:0x7f922cf87400.height == UILayoutGuide:0x600000c39260'UIViewLayoutMarginsGuide'.height   (active)>",
    "<NSLayoutConstraint:0x6000016764e0 'UIView-bottomMargin-guide-constraint' V:[UILayoutGuide:0x600000c39260'UIViewLayoutMarginsGuide']-(9)-|   (active, names: '|':_UIButtonBarStackView:0x7f922cd1d6e0 )>",
    "<NSLayoutConstraint:0x600001676440 'UIView-topMargin-guide-constraint' V:|-(10)-[UILayoutGuide:0x600000c39260'UIViewLayoutMarginsGuide']   (active, names: '|':_UIButtonBarStackView:0x7f922cd1d6e0 )>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x6000016764e0 'UIView-bottomMargin-guide-constraint' V:[UILayoutGuide:0x600000c39260'UIViewLayoutMarginsGuide']-(9)-|   (active, names: '|':_UIButtonBarStackView:0x7f922cd1d6e0 )>

Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKitCore/UIView.h> may also be helpful.

我煞费苦心地检查了我的故事板，并没有发现任何自动布局约束。

我在每个UIView 中实现了代码来禁用约束[self.view removeConstraints:self.view.constraints];

这可能是 Apple 的错误，因为它不会出现在实际设备上吗？

这是用户提示通过UIAlertController 进行登录和键盘输入的代码：

-(void) promptUserLogin
{
    NSString *alertTitle = @"User Login Required";
    NSString *alertMessage = @"Enter Email and Password";

    UIAlertController *alertController = [UIAlertController alertControllerWithTitle:alertTitle
                                                                             message:alertMessage
                                                                      preferredStyle:UIAlertControllerStyleAlert];

    [alertController addTextFieldWithConfigurationHandler:^(UITextField *textField)
     {
         textField.placeholder = @"User Email";
         [textField addTarget:self action:@selector(alertTextFieldDidChange:)
             forControlEvents:UIControlEventEditingChanged];
     }];

    [alertController addTextFieldWithConfigurationHandler:^(UITextField *textField)
     {
         textField.placeholder = @"User Password";
         textField.secureTextEntry = YES;
     }];

    UIAlertAction *cancelAction = [UIAlertAction actionWithTitle: @"Cancel"
                                                           style:UIAlertActionStyleCancel
                                                         handler:^(UIAlertAction *action)
                                   {
                                       NSLog(@"Cancel action");
                                   }];

    UIAlertAction *okAction = [UIAlertAction actionWithTitle: @"OK"
                                                       style:UIAlertActionStyleDefault
                                                     handler:^(UIAlertAction *action)
                               {
                                   UITextField *login = alertController.textFields.firstObject;
                                   UITextField *password = alertController.textFields.lastObject;

                                   NSLog(@"OK Action");
                                   NSLog(@"Login String: %@",login.text);
                                   NSLog(@"Password String: %@",password.text);
                               }];

    okAction.enabled = NO;
    [alertController addAction:cancelAction];
    [alertController addAction:okAction];

    //[self presentViewController:alertController animated:YES completion:nil];
    [self.navigationController presentViewController:alertController animated:YES completion:nil];
}

- (void)alertTextFieldDidChange:(UITextField *)sender
{
    UIAlertController *alertController = (UIAlertController *)self.presentedViewController;
    if (alertController)
    {
        UITextField *login = alertController.textFields.firstObject;
        UIAlertAction *okAction = alertController.actions.lastObject;
        okAction.enabled = login.text.length > 2;
    }
}

Answer 1

我认为这与您自己的布局问题无关。它与 InputAssistantItems（键盘上方）失败的自动布局约束有关。如果您查看自动布局错误中列出的第一个自动调整大小约束，它会引用 UIKeyboardAssistantBar。

关于如何重现它的更多细节：

当使用 inputAssistantItem 不包含任何自动更正建议的 UITextField 时（它是安全文本字段，或者它的 autocorrectionType 设置为 UIAutoCorrectionTypeNo），它会破坏自动布局约束（我只能在某些情况下重现它在 UITextFields 之间切换或辞职/变得活跃）。

这发生在两种情况下：

1. 文本字段的 autocorrectionType 设置为 UITextAutoCorrectionTypeNo。
2. 文本字段是安全文本字段。

在这两种情况下，中心 UIButtonBarStackView 都是空的（不包含自动更正建议）。

当您通过将前导/尾随 BarButtonGroups 设置为空数组来禁用 inputAssistantItem 或使用启用了自动更正的文本字段时，此问题不存在。

编辑：

详细说明一下，我不建议使用上述任何一种方法来解决此问题，因为您很可能会在安全文本字段中看到它，因为您引用了登录信息。相反，我的建议是忽略该警告，并在您认为合适的情况下将其报告为错误。