无法将 UIViewController 类型的值转换为 PatternDetailViewController [英] Can't cast value of type UIViewController to PatternDetailViewController

问题描述

我试图将视图控制器向下转换为详细视图控制器，但不能.我正在使用 Core Data(第一次).错误在 prepareForSegue 方法中，内容为:无法将类型为‘UIViewController’(0x1b81cdc)的值转换为‘Patternz.PatternDetailViewController’(0x32488).(lldb) "

Am trying to downcast a view controller to a detail view controller but can't. Am using Core Data (for the first time). The error is in the prepareForSegue method and reads: "Could not cast value of type 'UIViewController' (0x1b81cdc) to 'Patternz.PatternDetailViewController' (0x32488). (lldb) "

希望解释为什么它不起作用.这是文件.

Would appreciate an explanation of why it doesn't work. Here are the files.

ViewController.swift

ViewController.swift

import UIKit
import CoreData

class ViewController: UIViewController, UITableViewDataSource, UITableViewDelegate {

    @IBOutlet weak var tableView: UITableView!

    var patterns : [Pattern] = []

    var selectedPattern : Pattern? = nil


    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        self.tableView.dataSource = self
        self.tableView.delegate = self

        createTestPatterns()

        var context = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext!

        var request = NSFetchRequest(entityName: "Pattern")

        var results = context.executeFetchRequest(request, error: nil)

        if results != nil {
            self.patterns = results! as! [Pattern]
        }
    }

    func createTestPatterns() {
        var context = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext!

        var pattern = NSEntityDescription.insertNewObjectForEntityForName("Pattern", inManagedObjectContext: context) as! Pattern
        pattern.name = "Dress Shirt"
        pattern.frontimage = UIImageJPEGRepresentation(UIImage(named: "examplePattern.jpg"), 1)
        context.save(nil)
    }


    func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return self.patterns.count
    }

    func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
        var cell = UITableViewCell()
        var pattern = self.patterns[indexPath.row]
        cell.textLabel!.text = pattern.name
        cell.imageView!.image = UIImage(data: pattern.frontimage)
        return cell
    }

    func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
        self.selectedPattern = self.patterns[indexPath.row]
        self.performSegueWithIdentifier("patternDetailSegue", sender: self)
    }

    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
        if segue.identifier == "patternDetailSegue" {
            var detailViewController = segue.destinationViewController as! PatternDetailViewController // Could not cast value of type 'UIViewController' to 'Patternz.PatternDetailViewController'
            detailViewController.pattern = self.selectedPattern
        }
    }



}

PatternDetailViewController.swift

PatternDetailViewController.swift

import UIKit

class PatternDetailViewController: UIViewController {

    var pattern : Pattern? = nil

    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.

        self.navigationItem.title = self.pattern!.name
    }



}

推荐答案

正如您所说，问题出在以下几行:

The problem, as you have said, is in these lines:

if segue.identifier == "patternDetailSegue" {
    var detailViewController = segue.destinationViewController as! PatternDetailViewController 
    // Could not cast value of type 'UIViewController' to 'Patternz.PatternDetailViewController'

错误信息告诉你这个segue的destinationViewControllernot，实际上是一个PatternDetailViewController.你可能认为它是，但它不是.您需要检查故事板中的这个转场，看看它的目标端真正是什么.

The error message tells you that the destinationViewController of this segue is not, in fact, a PatternDetailViewController. You may think it is, but it isn't. You need to examine this segue in the storyboard and see what's really at the destination end of it.

错误消息将其描述为 UIViewController 的事实让我怀疑您忘记在故事板的此视图控制器的身份检查器中输入任何视图控制器类型:

The fact that the error message describes it as a UIViewController makes me suspect that you forgot to enter any view controller type in this view controller's Identity inspector in the storyboard:

这篇关于无法将 UIViewController 类型的值转换为 PatternDetailViewController的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！