相关疑难解决方法(0)

我有一个动态高度的视图,我试图在运行时更改此视图高度优先级.

这是我的代码部分;

if (index == 0) {

    surveyViewHeightConstraint.constant = 0;
    surveyViewHeightConstraint.priority = 1000;

} else if (index == 1) {

    surveyViewHeightConstraint.constant = 163;
    surveyViewHeightConstraint.priority = 500;

}

我正在用按钮动作改变索引.当我运行此代码时,我收到此错误:

*** Assertion failure in -[NSLayoutConstraint setPriority:], /SourceCache/Foundation/Foundation-1141.1/Layout.subproj/NSLayoutConstraint.m:174

这里的错误是什么？

在iOS 12.2上。使用UIAlertController的actionSheet Xcode时，遇到此问题的人都会遇到约束错误

相同的代码在iOS 12.1上运行，没有错误

我已经在Xcode 10.2和10.1上测试了此代码

class ViewController: UIViewController {

    let Click : UIButton = {
        let button = UIButton(type: UIButton.ButtonType.system)
        button.translatesAutoresizingMaskIntoConstraints = false
        button.setTitle("OK", for: .normal)
        button.tintColor = UIColor.blue
        button.addTarget(self, action: #selector(click(_:)), for: UIControl.Event.touchUpInside)
        return button
    }()

    override func viewDidLoad() {
        super.viewDidLoad()
        view.addSubview(Click)
        Click.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
        Click.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true
    }


    @objc func click(_ sender: UIButton) {
        let optionMenu = UIAlertController(title: nil, message: "Choose Option", preferredStyle: .actionSheet)

        let deleteAction = UIAlertAction(title: "Delete", style: .default)
        let saveAction = …

每当在模拟手机中显示UIAlertController操作表时，都会收到此警告。该代码没什么花哨的。

let action1 = UIAlertAction(title: "Action 1", style: .default) { _ in }
let action2 = UIAlertAction(title: "Action 2", style: .default) { _ in }
let cancel = UIAlertAction(title: "Cancel", style: .cancel, handler: nil)
let alert = UIAlertController(title: "title", message: "message", preferredStyle: .actionSheet)

alert.addAction(action1)
alert.addAction(action2)
alert.addAction(cancel)

self.present(alert, animated: true)

我正在运行Xcode 10.2（10E125），Swift5。该约束似乎超出了我的控制范围，但是请告知我是否做错了。