如何在同一视图控制器中的常规搜索之间展开搜索？

Question

抱歉，标题有点模糊。我仍在学习快速和连续学习，并且有3个名为EarthViewController，MoonViewController和JupiterViewController的视图控制器。

这些是有效的segue：

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

但是从MoonViewController -> EarthViewController开始放宽搜索时，在尝试返回“地球”视图时，我在Thread 1: Signal SIGABRT处添加了注释，并不断抛出//ERROR HERE错误。这是到目前为止的布局和代码：

EarthViewController（ViewController）

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")
        }
    }
}

MoonViewController

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）

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！

Answer 1

[C0中的此功能：

MoonViewController

既称为常规segue，也涉及放松segue。当您选择

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

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

时，JupiterViewController的类型确实为segue.destination。但是当您放松到JupiterViewController时，ViewController的类型为segue.destination。

在第二种情况下，强制类型ViewController由于类型错误而崩溃。

一种解决方法是，在确定目标位置后，将as! JupiterViewController的声明移到des的内部：

if