在主视图控制器中显示警报视图(从子类调用) [英] present alert view in main view controller (called from subclass)

问题描述

我的应用中有两个视图.一个主视图(ViewController.swift)和一个侧边栏(SideBar.swift).如果我点击侧边栏中的按钮，应该会显示 UIAlertView(我在 ViewController.swift 中调用了一个函数).但是应用程序崩溃了，因为主视图为零.你知道我该如何解决这个问题吗?

I have tow views in my app. A main view(ViewController.swift) and a sidebar(SideBar.swift). If I tapp a button in the sidebar an UIAlertViewshould be displayed (I call a function in ViewController.swift). But the app crashes because the main view is nil. Do you know how I can fix this?

我在函数中的代码(显示警报):

My code in the function (display alert):

    let alertView = UIAlertController(title: "You need to log in first", message: "To access the special features of the app you need to log in first.", preferredStyle: .Alert)
    alertView.addAction(UIAlertAction(title: "Login", style: .Default, handler: { (alertAction) -> Void in
    }))
    alertView.addAction(UIAlertAction(title: "Cancel", style: .Cancel, handler: nil))
    self.presentViewController(alertView, animated: true, completion: nil)

崩溃日志:

0x724160 <+60>:  bl     0x75961c                  ; function signature specialization <Arg[0] = Exploded, Arg[1] = Exploded> of Swift.(_fatalErrorMessage (Swift.StaticString, Swift.StaticString, Swift.StaticString, Swift.UInt) -> ()).(closure #2)
->  0x724164 <+64>:  trap   

推荐答案

我想到了两个解决方案.

There are two solutions that come to my mind.

1. 声明一个协议并使用委托将警报调用传递给 MainView.

首先，在我们的 SideBar.swift 中定义一个协议(我们称之为 AlertDelegate).

First, define a protocol in our SideBar.swift (Lets call it AlertDelegate).

 protocol AlertDelegate {

    func alertMain()

}

现在我们在 SideBar.swift 中创建一个委托变量.

Now we create a delegate variable in SideBar.swift.

var alertDelegate:AlertDelegate?

然后我们让 MainView (ViewController.swift) 遵守 AlertDelegate 协议.

Then we make our MainView (ViewController.swift) adhere to the AlertDelegate protocol.

class ViewController: UIViewController,foo,bar,AlertDelegate

并为 AlertDelegate 协议添加函数.您可以在此处放置 UIAlertController 代码.

And add in the function for the AlertDelegate protocol. Here is where you would put your UIAlertController code.

func alertMain(){

 //Present UIAlertController
}

最后，我们必须将 ViewController 设置为委托 alertDelegate

Finally, we have to set out ViewController to the delegate alertDelegate

1. 使用 AppDelegate KeyWindow 展示您的 UIAlertController.我可能不会推荐这种方法，但您可以这样做.

1. Present your UIAlertController using AppDelegate KeyWindow. I probably wouldn't recommend this method, but this is how you would do it.

 UIApplication.sharedApplication().keyWindow?.rootViewController?.presentViewController(alert, animated: true, completion: nil)

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