Question

我有一个闭包作为添加到UIAlertController的项的处理程序。我按预期收到了闭包内的id值。（我不会在代码段中使用它。）

但我遇到的问题是我想切换到另一个视图控制器。但我在封闭内部做了这个调用。

我收到以下错误： Value of type '(ChooseProfile) -> () -> (ChooseProfile)' has no member 'present＆＃39;

如何从闭包中切换到另一个视图控制器？

class ChooseProfile: UIViewController {
    let closure = { (id: String) in { (action: UIAlertAction!) -> Void in        
        let storyBoard : UIStoryboard = UIStoryboard(name: "Main", bundle:nil)
        let nextViewController = storyBoard.instantiateViewController(withIdentifier: "test") as! UIViewController
        self.present(nextViewController, animated:true, completion:nil)
    }}
}

我使用这个闭包是因为：

override func viewDidAppear(_ animated: Bool) {

        let alert = UIAlertController(title: "Choose a Device", message: "Which device would you like to use in this app?", preferredStyle: UIAlertControllerStyle.alert)

        for dev in (DataSingleton.instance.getDevices())! {
            alert.addAction(UIAlertAction(title: dev.getName(), style: UIAlertActionStyle.default, handler: closure(dev.getId())))
        }

        alert.addAction(UIAlertAction(title: "Add a new Profile", style: UIAlertActionStyle.destructive, handler: nil))


        // show the alert
        self.present(alert, animated: true, completion: nil)
    }

我根据设备列表添加警报操作。我想在点击设备时检索id。

Answer 1

问题是你在关闭时使用self，但是自己并没有引用VC的实例，因为它还没有完全创建。相反，为什么不在调用它时将viewController传递给闭包呢？

class ChooseProfile: UIViewController {
    let closure = { (id: String, vc: UIViewController) in { [weak vc] (action: UIAlertAction!) -> Void in        
        let storyBoard : UIStoryboard = UIStoryboard(name: "Main", bundle:nil)
        let nextViewController = storyBoard.instantiateViewController(withIdentifier: "test")
        vc?.present(nextViewController, animated:true, completion:nil)
    }}
}

override func viewDidAppear(_ animated: Bool) {

    let alert = UIAlertController(title: "Choose a Device", message: "Which device would you like to use in this app?", preferredStyle: UIAlertControllerStyle.alert)

    for dev in (DataSingleton.instance.getDevices())! {
        alert.addAction(UIAlertAction(title: dev.getName(), style: UIAlertActionStyle.default, handler: closure(dev.getId(), self)))
    }

    alert.addAction(UIAlertAction(title: "Add a new Profile", style: UIAlertActionStyle.destructive, handler: nil))


    // show the alert
    self.present(alert, animated: true, completion: nil)
}

从闭包中呈现视图控制器

1 个答案: