警告 - 尝试在 Swift 中呈现 UIAlertController null

Question

我有一个 UIAlertController 在我的项目中运行，它通过 UIButton 连接。我的代码工作正常。但是，每次当我按下按钮时，Xcode 控制台都会打印如下所示的警报，并且我经历了在 stackOverflow 中提出的所有类似问题但是没有答案。Attempt to present UIAlertController on UIViewController whose view is not in the window hierarchy

2016-10-03 19:14:35.854 xxxxxx[85186:7214348] Warning: Attempt to present<UIAlertController: 0x7f8d99450820>  on <yyyyyyy.ViewController: 0x7f8d9a025200> which is already presenting (null)

下面是我的代码：

    override func viewDidLoad() {
    super.viewDidLoad()

    self.moreButton.frame = CGRect(x:view.frame.width / 2, y: view.frame.height / 2, width: 100, height: 40)

    moreButton.center = view.center
    moreButton.backgroundColor = UIColor.darkText.withAlphaComponent(0.4)
    moreButton.layer.masksToBounds = true
    moreButton.setTitle("More", for: UIControlState())
    moreButton.setTitleColor(UIColor.white, for: UIControlState())
    moreButton.showsTouchWhenHighlighted = true
    moreButton.layer.cornerRadius = 5.0
    moreButton.addTarget(self, action: #selector(ViewController.moreButtonAction(_:)), for: .allTouchEvents)

    self.view.addSubview(self.moreButton)
    }


    func moreButtonAction(_ sender: UIButton) {

    DispatchQueue.main.async(execute: {

    let myAlert = UIAlertController(title: nil, message: nil, preferredStyle: UIAlertControllerStyle.actionSheet)
    myAlert.view.tintColor = UIColor.purple.withAlphaComponent(0.8)

    let myAction_1 = UIAlertAction(title: " Title 1", style: UIAlertActionStyle.default, handler: {
        (action: UIAlertAction!) in

    })

    let myAction_2 = UIAlertAction(title: " Title 2", style: UIAlertActionStyle.default, handler: {
        (action: UIAlertAction!) in

    })

    let myAction_3 = UIAlertAction(title: " Title 3", style: UIAlertActionStyle.default, handler: {
        (action: UIAlertAction!) in

    })

    let myAction_4 = UIAlertAction(title: "Cancel", style: UIAlertActionStyle.cancel, handler: {
        (action: UIAlertAction!) in
    })

    myAlert.addAction(myAction_1)
    myAlert.addAction(myAction_2)
    myAlert.addAction(myAction_3)
    myAlert.addAction(myAction_4)

    self.present(myAlert, animated: true, completion: nil)

    })
}

提前致谢

Answer 1

错误是告诉您您正在尝试呈现一个已经活动的alertController。您可以检查您的控制器是否有活动警报，否则会显示它。这将删除警告。所以基本上用以下内容移动你的self.present row：

if !(self.navigationController?.visibleViewController?.isKind(of: UIAlertController.self))! {
   self.present(myAlert, animated: true, completion: nil)
}

将您的 moreActionButton 函数替换为以下内容：

func moreButtonAction(_ sender: UIButton) {
    let myAlert = UIAlertController(title: nil, message: nil, preferredStyle: UIAlertControllerStyle.actionSheet)
    myAlert.view.tintColor = UIColor.purple.withAlphaComponent(0.8)

    let myAction_1 = UIAlertAction(title: " Title 1", style: UIAlertActionStyle.default, handler: {
        (action: UIAlertAction!) in

    })

    let myAction_2 = UIAlertAction(title: " Title 2", style: UIAlertActionStyle.default, handler: {
        (action: UIAlertAction!) in

    })

    let myAction_3 = UIAlertAction(title: " Title 3", style: UIAlertActionStyle.default, handler: {
        (action: UIAlertAction!) in
        print("3")

    })

    let myAction_4 = UIAlertAction(title: "Cancel", style: UIAlertActionStyle.cancel, handler: {
        (action: UIAlertAction!) in
    })

    myAlert.addAction(myAction_1)
    myAlert.addAction(myAction_2)
    myAlert.addAction(myAction_3)
    myAlert.addAction(myAction_4)

    if !(self.navigationController?.visibleViewController?.isKind(of: UIAlertController.self))! {
        self.present(myAlert, animated: true, completion: nil)
    }
}