无法将类型“[AnyObject]”的值转换为预期的参数类型“[String]”答案

【问题标题】：Cannot convert value of type '[AnyObject]' to expected argument type '[String]'无法将类型“[AnyObject]”的值转换为预期的参数类型“[String]”
【发布时间】：2016-07-08 19:29:06
【问题描述】：

当我尝试编译这段代码时：

func lookupPlayers() {
    print("Looking up \(match?.players.count)")
    
    // Loading ID from players connected in the match
    var idsArray = NSMutableArray()
    if (match != nil) {
        for players in match!.players {
            if let player = players as? GKPlayer {
                idsArray.addObject(player.playerID!)
            }
        }
        
    }
   
    GKPlayer.loadPlayersForIdentifiers(idsArray as [AnyObject] as [AnyObject], withCompletionHandler: { (players, error) -> Void in
        if (error != nil) {
            // Handle error here
            // if we fail to retrieve player info return and end the match
            print("Error retrieving player info: \(error.localizedDescription)")
            self.matchStarted = false
            self.delegate?.matchEnded?()
        }
        else {
            // Get info from all players and start the match
            self.playersDict = NSMutableDictionary(capacity: players.count)
            for player1 in players {
                if let player = player1 as? GKPlayer {
                    print("Found player: \(player.alias)")
                    self.playersDict.setObject(player, forKey: player.playerID)
                }
            }
            self.playersDict.setObject(self.localPlayer, forKey: self.localPlayer.playerID)
            
            self.matchStarted = true
            self.delegate?.matchStarted?()
        }
    })
}

我收到此错误：

无法在此行中将类型“[AnyObject]”的值转换为预期的参数类型“[String]”：
GKPlayer.loadPlayersForIdentifiers(idsArray as [AnyObject] as [AnyObject], withCompletionHandler: { (players, error) -> Void in

我做错了什么？

【问题讨论】：

首先错误告诉你[AnyObject]应该是[String]。其次，为什么会有as [AnyObject] as [AnyObject]。我认为第二个as [AnyObject] 没用。这就好比说把这个对象当成一辆车，它被当成一辆车。没有意义。您是否尝试过简单地将 [AnyObject] 替换为 [String] 并删除该行中的重复项？

标签： swift

【解决方案1】：

与这个问题非常相似： Problems with code when updating to Swift 2.0. “Cannot convert value..”

如您所知，您需要将[String] 传递给loadPlayersForIdentifiers(_:withCompletionHandler:) 的第一个参数。还有playerId! 绝对是String。为什么你NSMutableArray知道这个？

将idsArray的声明改为：

    var idsArray: [String] = []

导致错误的行：

    GKPlayer.loadPlayersForIdentifiers(idsArray, withCompletionHandler: { (players, error) -> Void in

【讨论】：

【解决方案2】：

尝试以下方法：

将var idsArray = NSMutableArray() 替换为var idsArray = [String]()。这样你就可以使用 Swift 数组，而不是 Obj-C NSArrays。
然后替换：

GKPlayer.loadPlayersForIdentifiers(idsArray as [AnyObject] as [AnyObject], withCompletionHandler: { (players, error) -> Void in if (error != nil) {

与：

GKPlayer.loadPlayersForIdentifiers(idsArray as [String], withCompletionHandler: { (players, error) -> Void in if (error != nil) {

【讨论】：

【解决方案3】：

尝试将 idArray 声明为 Array<String>() 而不是 NSMutableArray()。

像这样：

// Loading ID from players connected in the match
    var idsArray = Array<String>()
    if (match != nil) {
        for players in match!.players {
            if let player = players as? GKPlayer {
                idsArray.append(player.playerID!)
            }
        }

    }

    GKPlayer.loadPlayersForIdentifiers(idsArray, withCompletionHandler: { (players, error) -> Void in
        if (error != nil) {
            // Handle error here
         ...
}
    })

【讨论】：