Question

可以通过以下简单项目重现该问题：

当用户单击导航栏上的+按钮时，代码将实例化并以操作表样式显示UIAlertController。

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
    }

    @IBAction func buttonTapped(_ sender: Any) {
        let actionSheet = UIAlertController(title: nil,
                                            message: nil,
                                            preferredStyle: .actionSheet)
        actionSheet.addAction(UIAlertAction(title: "Create Income",
                                            style: .default) { _ in
                                                print("Income!") })
        actionSheet.addAction(UIAlertAction(title: "Create Outcome",
                                            style: .default) { _ in
                                                print("Outcome!")})
        actionSheet.addAction(UIAlertAction(title: "Cancel", style: .cancel) { _ in })
        self.present(actionSheet, animated: true, completion: nil)
    }
}

UI正确显示。问题是出现操作表时，Xcode会发出以下自动布局警告：

2020-03-12 11:24:57.002113+0800 alertcontroler_test[12757:936231] [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:0x600002d11b30 UIView:0x7f851961c560.width == - 16   (active)>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x600002d11b30 UIView:0x7f851961c560.width == - 16   (active)>

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.

当操作表显示时，我检查Xcode中的UI层次结构，并发现一些子视图后带有感叹号：

我在Google上对此进行了搜索，但没有发现有人报告类似的问题（即UIAlertController出现时的自动布局警告）。我找到一些有关如何在UIViewAlertForUnsatisfiableConstraints()上设置断点以及如何调试汇编代码的信息。但是我认为这是UIAlertController中的一个内部问题，我创建和展示UIAlertController的方式是常见和典型的。有什么建议我应该做什么？

可以在最新版本的Xcode（11.3.1）和iOS（13.3）上找到。如果我将样式更改为警报，则问题不再存在。任何帮助将不胜感激。

Answer 1

这是Apple团队无法修复的错误，该错误与与动画有关的警报和操作表有关。您可以点击以下链接进行验证：-

UIAlertController's actionSheet gives constraint error on iOS 12.2 / 12.3

Swift default AlertViewController breaking constraints

解决方案是将动画值传递为false，例如：-

GetProperty("AEVL2021")

我展示了没有动画的UIAlertController，警告消失了。

或者您可以尝试在stackoverflow的链接之一中提到的此解决方案：-

1Maria Del Mundo290
2Jay Del Mundo2220

呈现UIAlertController（以动作表样式）引起神秘的自动布局警告

1 个答案: