ios - 如何在同一个 View Controller 中使常规任务在常规任务之间正常工作？

对不起，如果标题有点模糊。我还在学习swift和segues，我有3个视图控制器，分别叫做EarthViewController、MoonViewController和JupiterViewController。
以下是有效的部分：

EarthViewController -> MoonViewController
MoonViewController -> JupiterViewController
JupiterViewController -> MoonViewController,
and even JupiterViewController -> EarthViewController,

但是当我试图返回地球视图时，从MoonViewController -> EarthViewController开始的展开段不断抛出一个Thread 1: Signal SIGABRT错误。以下是迄今为止的布局和代码：

EarthViewController（视图控制器）

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
    }

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        let des = segue.destination as! MoonViewController

        if (segue.identifier == "toMoonView")
        {
            print("Went to the moon")
        }
    }

    @IBAction func backFromMoon(segue: UIStoryboardSegue){

        if let scVC = segue.source as? MoonViewController
        {
            print ("Back from the Moon to Earth")
        }
    }

    @IBAction func backFromJupiterToEarth(segue: UIStoryboardSegue){

        if let scVC = segue.source as? JupiterViewController
        {
            print ("Back from Jupiter to Earth")
        }
    }
}

月光控制器

import UIKit

class MoonViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.
    }

//------------------------------------------------------------------------
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        let des = segue.destination as! JupiterViewController //<- ERROR HERE

        if (segue.identifier == "toJupiterView")
        {
            print("Went to Jupiter")
        }
    }
//-----------------------------------------------------------------------
    @IBAction func backFromJupiter(segue: UIStoryboardSegue){

        if let scVC = segue.source as? JupiterViewController
        {
            print ("Back from Jupiter to the Moon")
        }
    }
}

JupiterViewController（尚未添加任何内容）

import UIKit

class JupiterViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.
    }


}

非常感谢您的帮助！谢谢您！

最佳答案

此函数在MoonViewController中：

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    let des = segue.destination as! JupiterViewController //<- ERROR HERE

    if (segue.identifier == "toJupiterView")
    {
        print("Went to Jupiter")
    }
}

称为规则分段和展开分段。当您开始JupiterViewController时，segue.destination确实是JupiterViewController类型。但当您展开到ViewController时，segue.destination属于ViewController类型。
在第二种情况下，force castas! JupiterViewController由于类型错误而崩溃。
解决这个问题的一种方法是，当您确定了目的地后，将des的声明移到if中：

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if segue.identifier == "toJupiterView"
    {
        let des = segue.destination as! JupiterViewController
        print("Went to Jupiter")
    }
}