swift - 无法避免 optional() 用于字符串打印语句？

Question

我有一个包含一些字符串参数的数据结构。结构如下:

struct pulledMessage{
    var convoWithUserID: String
    var convoWithUserName: String
}

我有一个函数，它根据特定 pulledMessage 中的值为变量赋值。由于某些更复杂、超出问题范围的原因，这些值来自 [pulledMessage] 数组。 pulledMessage 在实际函数中总是会发生变化，但为了便于说明，我将其写为常量:

var messageArray = [pulledMessage]()


func assignValues(){
    messageArray.append(pulledMessage(convoWithUserID: "abc123", convoWithUserName: "Kevin"))
    let convoWithUserID = messageArray[0].convoWithUserID
    let convoWithUserName = messageArray[0].convoWithUserName
    print(convoWithUserID) //returns optional("abc123")
    print(convoWithUserName) // returns optional("Kevin")
}

我尝试添加 ! 以不同方式解包值:

messageArray[0]!.convoWithUserID

这告诉我一个错误，我无法打开非可选类型的 pulledMessage。

messageArray[0].convoWithUserID!

这给了我一个错误，我无法打开非可选类型的字符串。
This stack question建议利用 if let 摆脱可选的:

if let convoWithUserIDCheck = messageArray[0].convoWithUserID{
    convoWithUserID = convoWithUserIDCheck
}

这给了我一个警告，没有理由对非可选类型的字符串执行 if let。我不知道如何让它停止返回 optional() 包装的值。

更新:更复杂、更完整的代码

SQL 数据库函数:

class FMDBManager: NSObject {
    static let shared: FMDBManager = FMDBManager()


let databaseFileName = "messagesBetweenUsers.sqlite"

var pathToDatabase: String!

var database: FMDatabase!

override init() {
    super.init()

    let documentsDirectory = (NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)[0] as NSString) as String
    pathToDatabase = documentsDirectory.appending("/\(databaseFileName)")
}
func loadMessageData(){//will need a struct to load the data into a struct


    if openDatabase(){
        let query = "select * from messages order by messageNumber asc"
        do{
            print(database)
            let results: FMResultSet = try database.executeQuery(query, values: nil)

            while results.next(){

                let message = pulledMessage(convoWithUserID: String(describing: results.string(forColumn: "convoWithUserID")), convoWithUserName: String(describing: results.string(forColumn: "convoWithUserName")), messageString: String(describing: results.string(forColumn: "messageString")), senderID: String(describing: results.string(forColumn: "senderID")), timeSent: String(describing: results.string(forColumn: "timeSent")), messageNumber: Int(results.int(forColumn: "messageNumber")))
                if messagesPulled == nil{
                    messagesPulled = [pulledMessage]()
                }
                messagesPulled.append(message)
                print("The message that we have pulled are \(message)")
            }

        }
        catch{
            print(error.localizedDescription)
        }

        database.close()
    }


}
}

在应用启动时运行数据填充:

    func applicationDidBecomeActive(_ application: UIApplication) {
//        if FMDBManager.shared.createDatabase() {
//            FMDBManager.shared.insertMessageData()
//        }else{
//            print("Not a chance, sonny")
//            FMDBManager.shared.insertMessageData()
//        }
        FMDBManager.shared.loadMessageData()
    }

按顺序组织 SQL 数据:

struct pulledMessage{//global struct
    var convoWithUserID: String
    var convoWithUserName: String
    var messageString: String
    var senderID: String
    var timeSent: String
    var messageNumber: Int
}

var messagesPulled: [pulledMessage]!

var messageConvoDictionary = [String: [pulledMessage]]()
//For the individual message convos
    var fullUnorderedMessageArray = [[pulledMessage]]()
    var fullOrderedMessageArray = [[pulledMessage]]()

    //For the message table
    var unorderedLastMessageArray = [pulledMessage]()
    var orderedLastMessageArray = [pulledMessage]()




    //For the table messages... FROM HERE..........................................
    func organizeSQLData(messageSet: [pulledMessage]){
        var i = 0
        var messageUserID = String()
        while i < messageSet.count{
            if (messageSet[i]).convoWithUserID != messageUserID{
                print("It wasn't equal")
                print(messageSet[i])
                messageUserID = messageSet[i].convoWithUserID
                if messageConvoDictionary[messageUserID] != nil{
                    messageConvoDictionary[messageUserID]?.append(messageSet[i])
                }else{
                    messageConvoDictionary[messageUserID] = []
                    messageConvoDictionary[messageUserID]?.append(messageSet[i])
                }
                i = i + 1
            }else{
                messageConvoDictionary[messageUserID]?.append(messageSet[i])
                i = i + 1
            }
        }

    }


    func getLastMessages(messageSet: [String:[pulledMessage]]){

        for (_, messages) in messageSet{
            let orderedMessages = messages.sorted(by:{ $0.timeSent.compare($1.timeSent) == .orderedAscending})
            let finalMessage = orderedMessages[0]
            unorderedLastMessageArray.append(finalMessage)
        }
        print(unorderedLastMessageArray)
    }

    func orderLastMessage(messageSet: [pulledMessage]){
        orderedLastMessageArray = messageSet.sorted(by:{ $0.timeSent.compare($1.timeSent) == .orderedDescending})
        messagesListTableView.reloadData()
        print("It wasn't\(orderedLastMessageArray)")
    }


    func getMessagesReady(){//for observer type function calls
        organizeSQLData(messageSet: messagesPulled)
        getLastMessages(messageSet: messageConvoDictionary)
        orderLastMessage(messageSet: unorderedLastMessageArray)
        //This one is for the individual full convos for if user clicks on a cell... its done last because its not required for the page to show up
        orderedFullMessageConvos(messageSet: messageConvoDictionary)
        let openedMessageConversation = fullOrderedMessageArray[(indexPath.row)]//not placed in its appropriate location, but it is just used to pass the correct array (actually goes in a prepareforSegue)

    }
     override func viewDidLoad() {
            super.viewDidLoad()
           getMessagesReady()
        }

然后转到新 Controller (将 openedMessageConversation 传递给 messageConvo)并在单击按钮时运行此过程:

let newMessage = pulledMessage(convoWithUserID: messageConvo[0].convoWithUserID, convoWithUserName: messageConvo[0].convoWithUserName, messageString: commentInputTextfield.text!, senderID: (PFUser.current()?.objectId)!, timeSent: String(describing: Date()), messageNumber: 0)
            messageConvo.append(newMessage)
            let newMessageSent = PFObject(className: "UserMessages")
            newMessageSent["convoWithUserID"] = newMessage.convoWithUserID
            newMessageSent["convoWithUserName"] = newMessage.convoWithUserName
            newMessageSent["messageString"] = newMessage.messageString
            newMessageSent["senderID"] = newMessage.senderID
            let acl = PFACL()
            acl.getPublicWriteAccess = true
            acl.getPublicReadAccess = true
            acl.setWriteAccess(true, for: PFUser.current()!)
            acl.setReadAccess(true, for: PFUser.current()!)
            newMessageSent.acl = acl
            newMessageSent.saveInBackground()

是newMessageSent["convoWithUserID"]和newMessageSent["convoWithUserName"]在数据库中用optional()读取。

Answer 1

原来这个原因源于loadMessageData运行的函数。 String(describing: results.string(forColumn:) 的使用需要对 results.String(forColumn:)! 进行解包。此问题在整个数据修改过程中传播整个应用程序并导致我看到的打印语句的 optional() 包装。