ios - 无法在强制转换中将类型 '[Record]' 的值转换为类型 'Record'

Question

我将使用 C# 和 Xamarin 制作的 iOS 应用重写到 Swift，原因很明显是 Xamarin 的定价和低文档。正在关注this tutorial因为在我的 UITableView 上包含一个 UISearchBar，我遇到了这个错误:Cannot convert value of type '[Record]' to type 'Record in coercion。 Record.swift 是我创建的一个结构文件，用于存储我将使用 cloudkit 检索的数据，但我不确定这个错误是怎么来的。

这是 MasterViewController.swift 的问题部分:

func updateSearchResultsForSearchController(searchController: UISearchController) {
    self.filteredRecords.removeAll(keepCapacity: false)

    let searchPredicate = NSPredicate(format: "SELF CONTAINS [c] %@", searchController.searchBar.text!)
    // Here is where the error shows
    let array = (self.records as Record).filteredArrayUsingPredicate(searchPredicate)
    self.filteredRecords = array as! [Record]

    self.tableView.reloadData()
}

这是完整的 MasterViewController.swift:

import UIKit

class MasterViewController: UITableViewController, UISearchResultsUpdating {

    var detailViewController: DetailViewController? = nil
    var resultSearchController = UISearchController()
    var records = [Record]()
    var filteredRecords = [Record]()

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

        let addButton = UIBarButtonItem(barButtonSystemItem: .Add, target: self, action: "insertNewObject:")
        self.navigationItem.rightBarButtonItem = addButton
        if let split = self.splitViewController {
            let controllers = split.viewControllers
            self.detailViewController = (controllers[controllers.count-1] as! UINavigationController).topViewController as? DetailViewController
        }

        // #REMOVE - Testing implementation until iCloud is setup
        self.records = [
            Record(album: "The Awakening", artist: "P.O.D.",  genre: "Hardcore Rock", year: 2015, speed: "33 1/3", size: 12),
            Record(album: "Attack of The Killer B-Sides", artist: "A Day to Remember",  genre: "Post-Hardcore", year: 2010, speed: "33 1/3", size: 7),
            Record(album: "All I Want", artist: "A Day to Remember",  genre: "Post-Hardcore", year: 2011, speed: "33 1/3", size: 7),
            Record(album: "The White Stripes", artist: "The White Stripes",  genre: "Rock", year: 2003, speed: "45", size: 7),
            Record(album: "Save Rock and Roll", artist: "Fall Out Boy",  genre: "Punk Rock", year: 2013, speed: "33 1/3", size: 10),
            Record(album: "A Perfect Sky", artist: "Yellowcard",  genre: "Pop-Punk", year: 2015, speed: "33 1/3", size: 10),
            Record(album: "Noise vs Beauty", artist: "Bassnectar",  genre: "Dubstep", year: 2014, speed: "33 1/3", size: 12)
        ]

        // Configure the search bar controller
        self.resultSearchController = UISearchController(searchResultsController: nil)
        self.resultSearchController.searchResultsUpdater = self
        self.resultSearchController.dimsBackgroundDuringPresentation = false
        self.resultSearchController.searchBar.sizeToFit()

        self.tableView.tableHeaderView = self.resultSearchController.searchBar

        // Reload the data upon startup
        self.tableView.reloadData()
    }

    override func viewWillAppear(animated: Bool) {
        self.clearsSelectionOnViewWillAppear = self.splitViewController!.collapsed
        super.viewWillAppear(animated)
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

//    func insertNewObject(sender: AnyObject) {
//        objects.insert(NSDate(), atIndex: 0)
//        let indexPath = NSIndexPath(forRow: 0, inSection: 0)
//        self.tableView.insertRowsAtIndexPaths([indexPath], withRowAnimation: .Automatic)
//    }

    // MARK: - Segues

    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
        if segue.identifier == "showDetail" {
            if let indexPath = self.tableView.indexPathForSelectedRow {
                let object = records[indexPath.row]
                let controller = (segue.destinationViewController as! UINavigationController).topViewController as! DetailViewController
                controller.detailItem = object
                controller.navigationItem.leftBarButtonItem = self.splitViewController?.displayModeButtonItem()
                controller.navigationItem.leftItemsSupplementBackButton = true
            }
        }
    }

    // MARK: - Table View

    override func numberOfSectionsInTableView(tableView: UITableView) -> Int {
        return 1
    }

    override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        if (self.resultSearchController.active) {
            return self.filteredRecords.count
        } else {
            return self.records.count
        }
    }

    override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCellWithIdentifier("Cell", forIndexPath: indexPath) as UITableViewCell

        if (self.resultSearchController.active) {
            let object = filteredRecords[indexPath.row]
            cell.textLabel!.text = object.album
            cell.detailTextLabel!.text = object.artist
            cell.accessoryType = UITableViewCellAccessoryType.DisclosureIndicator
        } else {
            let object = records[indexPath.row]
            cell.textLabel!.text = object.album
            cell.detailTextLabel!.text = object.artist
            cell.accessoryType = UITableViewCellAccessoryType.DisclosureIndicator
        }

        return cell
    }

    override func tableView(tableView: UITableView, canEditRowAtIndexPath indexPath: NSIndexPath) -> Bool {
        // Return false if you do not want the specified item to be editable.
        return true
    }

    override func tableView(tableView: UITableView, commitEditingStyle editingStyle: UITableViewCellEditingStyle, forRowAtIndexPath indexPath: NSIndexPath) {
        if editingStyle == .Delete {
            records.removeAtIndex(indexPath.row)
            tableView.deleteRowsAtIndexPaths([indexPath], withRowAnimation: .Fade)
        } else if editingStyle == .Insert {
            // Create a new instance of the appropriate class, insert it into the array, and add a new row to the table view.
        }
    }

    func updateSearchResultsForSearchController(searchController: UISearchController) {
        self.filteredRecords.removeAll(keepCapacity: false)

        let searchPredicate = NSPredicate(format: "SELF CONTAINS [c] %@", searchController.searchBar.text!)
        let array = (self.records as Record).filteredArrayUsingPredicate(searchPredicate)
        self.filteredRecords = array as! [Record]

        self.tableView.reloadData()
    }
}

和 Record.swift:

import Foundation

struct Record {
    let album : String
    let artist : String
    let genre : String
    let year : Int
    let speed : String
    let size : Int
}

希望这将是一个简单的修复。如果没有，是否有任何教程建议？或者其他地方我应该问这个？

Answer 1

filteredArrayUsingPredicate 是一个 NSArray 方法，因此您应该将其转换为 NSArray:

let array = (self.records as NSArray).filteredArrayUsingPredicate(searchPredicate)

但这仍然会产生错误“[Record] 无法转换为 NSArray”。这是因为 NSArray 只能包含 Objective-C 对象，而 Record 是 Swift 结构，不能转换为对象。有两种解决方案。

解决方案一:

将记录声明为一个对象

class Record: NSObject {
    let album : String
    let artist : String
    let genre : String
    let year : Int
    let speed : String
    let size : Int

    init(album : String, artist : String, genre : String, year : Int, speed : String, size : Int) {
        self.album = album
        self.artist = artist
        self.genre = genre
        self.year = year
        self.speed = speed
        self.size = size
    }
}

那么下面的代码应该可以工作了

let searchPredicate = NSPredicate(format: "SELF.artist CONTAINS [c] %@", searchController.searchBar.text!)
let array = (self.records as NSArray).filteredArrayUsingPredicate(searchPredicate)
self.filteredRecords = array as! [Record]

请注意，您的原始谓词没有意义，并且会导致运行时错误，因为 Record 不是字符串，所以我将其替换。

解决方案 2:

使用Swift方式过滤:

let searchText = searchController.searchBar.text!.lowercaseString
filteredRecords = self.records.filter { (aRecord) -> Bool in
    return aRecord.artist.lowercaseString.containsString(searchText)
}