Ios 在segue之后查看出口零

我正在参加斯坦福IOS在线开发课程，有一个bug我不知道如何处理。当我在分割视图控制器中切换到详图视图时，我能够从插座didSet中的详图UIViewController设置详图UIView的参数。稍后，当我尝试从控制器访问或修改细节视图时，视图变量（outlet）为零，即使视图仍在屏幕上并响应手势。 这是分割视图控制器中主视图的准备方法

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {  
    let destinationViewController = segue.destination  
    if let graphViewController = destinationViewController as? GraphViewController {  
        if let identifier = segue.identifier{  
            switch identifier {  
            case "DisplayGraph":  
                graphViewController.function = funcForGraphView(_:)  
            default:  
                break  
            }  
        }  
    }  
}  

这是详图视图控制器。我评论了有趣的部分

class GraphViewController: UIViewController {  
@IBOutlet weak var graphView: GraphView!{  
    didSet{  
        graphView.addGestureRecognizer(UITapGestureRecognizer(target: graphView, action: #selector(graphView.tap(recognizer:))))  
        graphView.addGestureRecognizer(UIPanGestureRecognizer(target: graphView, action: #selector(graphView.pan(recognizer:))))  
        graphView.addGestureRecognizer(UIPinchGestureRecognizer(target: graphView, action: #selector(graphView.zoom(recognizer:))))  
        graphView.function = cos //I can set variables in the view here  
        // After this didSet I am no longer able to set or read any variables from the graphView  
    }  
}  
var function: ((Double)->(Double))? {  
    didSet{  
        if let newfunction = function {  
            graphView.function = newfunction // I can not set or access variables in the view here since for some reason graphView is nil  
        }  
    }  
}  

这是详图视图中的相关变量

var function: ((Double) -> Double)? {  
    didSet{  
        setNeedsDisplay()  
    }  
}  

任何帮助都将不胜感激，希望这不是一个愚蠢的问题。如果更多的信息会有帮助，让我知道。

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谢谢

它将为零，因为在推送viewcontrolle时您的视图未完全加载。因此，您需要通过以下考试：

在图形视图控制器中

var yourValue : ((Double)->(Double))?

override func viewDidLoad() {
        super.viewDidLoad()
         self.function = yourValue
}

导航时设置值

 if let identifier = segue.identifier{  
            switch identifier {  
            case "DisplayGraph":  
                graphViewController.yourValue = funcForGraphView(_:)  
            default:  
                break  
            }  
        } 

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非常感谢你，真是帮了大忙。