安全解决方案

Question

我正在尝试使用样式为 .actionSheet 的默认AlertViewController。由于某种原因，该警报会导致约束错误。只要没有通过按钮触发（显示）alertController，整个视图就不会出现约束错误。难道这是Xcode的 bug？

我得到的确切错误如下：

2019-04-12 15:33:29.584076+0200 Appname[4688:39368] [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. 
(
    "<NSLayoutConstraint:0x6000025a1e50 UIView:0x7f88fcf6ce60.width == - 16   (active)>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x6000025a1e50 UIView:0x7f88fcf6ce60.width == - 16   (active)>

这是我使用的代码：

@objc func changeProfileImageTapped(){
        print("ChangeProfileImageButton tapped!")
        let alert = UIAlertController(title: "Change your profile image", message: nil, preferredStyle: .actionSheet)

        alert.addAction(UIAlertAction(title: "Photo Library", style: .default, handler: nil))
        alert.addAction(UIAlertAction(title: "Online Stock Library", style: .default, handler: nil))
        alert.addAction(UIAlertAction(title: "Cancel", style: .cancel, handler: nil))
        alert.view.tintColor = ColorCodes.logoPrimaryColor

        self.present(alert, animated: true)
    }

如您所见，它是非常基础。这就是为什么我对我得到的奇怪行为感到非常困惑，因为这种默认实现不会引起任何错误，对吧？

尽管通过打破限制，警报可以在所有屏幕尺寸上正确显示，但我非常感谢我能提供的任何帮助。

Answer 1

以下内容删除了警告，而无需禁用动画。并且假设苹果最终解决了警告的根本原因，那么它就不会破坏其他任何东西。

-:77.294: Opening and ending tag mismatch: img line 77 and a
 middle;" src="/Content/images/gongshangbiaoshi.gif" alt="" class="footpic"></a>
                                                                               ^
-:77.301: Opening and ending tag mismatch: a line 77 and span
;" src="/Content/images/gongshangbiaoshi.gif" alt="" class="footpic"></a></span>
                                                                               ^
-:77.332: Opening and ending tag mismatch: span line 77 and p
i.gif" alt="" class="footpic"></a></span><br />©2014-2018中国知网(CNKI) </p
                                                                               ^
-:79.15: Opening and ending tag mismatch: p line 74 and div
        </div>
              ^
-:92.8: Opening and ending tag mismatch: div line 61 and body
</body>
       ^
-:93.8: Opening and ending tag mismatch: body line 11 and html
</html>
       ^
-:94.1: Premature end of data in tag html line 2

^

然后可以这样使用：

            var findResult = _coll.Find(cnFilter & orderDateFilter & deliveryDateFilter & statusFilter & keywordFilter);
            var countResult = _coll.Find(cnFilter & orderDateFilter & deliveryDateFilter & statusFilter & keywordFilter).CountDocumentsAsync();

Answer 2

此错误并不严重，似乎是Apple修复的错误。出现后，此约束以动画样式显示。我尝试在呈现之前对其进行捕获和更改（更改值，关系，优先级）–由于这种动态添加的限制，因此没有成功。

当您在self.present(alert, animated: false)中关闭动画并使用alert.view.addSubview(UIView())时，错误消失了。我无法解释，但是可以！

let alert = UIAlertController(title: "Change your profile image", message: nil, preferredStyle: .actionSheet)

alert.addAction(UIAlertAction(title: "Photo Library", style: .default, handler: nil))
alert.addAction(UIAlertAction(title: "Online Stock Library", style: .default, handler: nil))
let cancel = UIAlertAction(title: "Cancel", style: .destructive, handler: nil)

alert.addAction(cancel)
alert.view.addSubview(UIView()) // I can't explain it, but it works!

self.present(alert, animated: false)

Answer 3

添加到this答案...这似乎为我消除了该问题，并且不需要对现有代码进行任何更改。

extension UIAlertController {
    override open func viewDidLoad() {
        super.viewDidLoad()
        pruneNegativeWidthConstraints()
    }

    func pruneNegativeWidthConstraints() {
        for subView in self.view.subviews {
            for constraint in subView.constraints where constraint.debugDescription.contains("width == - 16") {
                subView.removeConstraint(constraint)
            }
        }
    }
}

Answer 4

这是iOS版本中的新错误：

12.2
12.3
12.4
13.0
13.1
13.2
13.2.3
13.3

我们唯一能做的就是向Apple提交错误报告（我只是这样做，您也应该这样做）。

我将尝试发布新版本的iOS的答案。

Answer 5

安全解决方案

您不应删除该约束，因为将来会以正确的值使用该约束。

或者，您可以将其常数更改为正值：

class PXAlertController: UIAlertController {
    override func viewDidLoad() {
        super.viewDidLoad()

        for subview in self.view.subviews {
            for constraint in subview.constraints {
                if constraint.firstAttribute == .width && constraint.constant == -16 {
                    constraint.constant = 10 // Any positive value
                }
            }
        }
    }
}

然后使用以下命令初始化您的控制器：

let controller = PXAlertController(title: "Title", message: "Message", preferredStyle: .actionSheet)

Answer 6

摆脱NSLayoutConstraint错误的另一种方法是使用preferredStyle: .alert而不是preferredStyle: .actionSheet。此方法不会产生警告，但会以模态显示菜单。

Answer 7

Objective-C的解决方案：

从UIAlertController继承您自己的警报控制器

定义修剪功能，如上一个回复

@implementation TemplateAlertController

-(void) viewDidLoad {

    [super viewDidLoad];
    [self mPruneNegativeWithConstraints];
}

-(void) mPruneNegativeWithConstraints {

    for (UIView* iSubview in [self.view subviews]) {
        for (NSLayoutConstraint* iConstraint in [iSubview constraints]) {
            if ([iConstraint.debugDescription containsString:@"width == - 16"]) {
                [iSubview removeConstraint:iConstraint];
            }
        }
    }
}

@end

Answer 8

有趣的想法在这里。我个人不喜欢删除约束或更改其值（大小）的想法。

由于问题取决于约束解决方案被迫达到必须打破强制性（优先级1000）约束的位置，因此，一种比较不残酷的方法只是告诉框架，如果需要，可以打破此约束。

所以（基于Josh的“安全”类）：

class PXAlertController: UIAlertController {
    override func viewDidLoad() {
        super.viewDidLoad()
        tweakProblemWidthConstraints()
    }
    
    func tweakProblemWidthConstraints() {
        for subView in self.view.subviews {
            for constraint in subView.constraints {
                // Identify the problem constraint
                // Check that it's priority 1000 - which is the cause of the conflict.
                if constraint.firstAttribute == .width &&
                    constraint.constant == -16 &&
                    constraint.priority.rawValue == 1000 {
                    // Let the framework know it's okay to break this constraint
                    constraint.priority = UILayoutPriority(rawValue: 999)
                }
            }
        }
    }
}

它的优点是它不会更改任何布局尺寸，而且在框架修复的情况下，也很有可能表现良好。

在iPhone SE模拟器中进行了测试（这使我遇到了最初的问题）-与约束相关的调试已消失。

Answer 9

如果要保留动画和所有约束，则应在呈现警报控制器之前找到一个负约束并将其设为正。

// Find negative constraint and make it positive
for subview in alert.view.subviews {
    for constraint in subview.constraints {
        if constraint.constant < 0 {
            constraint.constant = -constraint.constant
        }
    }
}

// Present alert controller
present(alert, animated: true)

Answer 10

这里是我用来解决问题的函数。出现问题是因为约束是负的，我不知道为什么。

    func showActionSheet(title: String, message: String, actions: [UIAlertAction]) {
        let alertController = UIAlertController(title: title, message: message, preferredStyle: .actionSheet)
        actions.forEach { alertController.addAction($0) }
        let subviewConstraint = alertController.view.subviews
            .flatMap({ $0.constraints })
            .filter({ $0.constant < 0 })
        for subviewConstraint in subviewConstraint {
            subviewConstraint.constant = -subviewConstraint.constant // this is the answer
        }
        self.present(alertController, animated: true)
    }

Answer 11

创建视图扩展以获取所有约束

extension UIView {
   func callRecursively(_ body: (_ subview: UIView) -> Void) {
      body(self)
      subviews.forEach { $0.callRecursively(body) }
}}

创建 UIAlertController 扩展以查找所有具有 -16 常量的约束并将其优先级更改为 999

extension UIAlertController {
   func fixConstraints() -> UIAlertController {
      view.callRecursively { subview in
         subview.constraints
            .filter({ $0.constant == -16 })
            .forEach({ $0.priority = UILayoutPriority(rawValue: 999)})
    }
    return self
}}

创建您的提醒并在演示时调用 fixConstraints()：

let alert = UIAlertController(...
...
present(alert.fixConstraints(), animated: true, completion: nil)

Swift默认AlertViewController突破约束

11 个答案:

安全解决方案