iOS Swift 3 CompletionHandler 不工作

Question

我正在尝试在 Swift 中编写一个完成处理程序函数，这是我在 Swift 中的代码，其中包含一个名为 NBObject

的 class

typealias CompletionHandler = (_ success: Bool, _ data: [String:Any]) -> Void

// FIND OBJECTS IN BACKGROUND
func findObjectInBackground(completionHandler: CompletionHandler) {
    let tbNameStr = "table=" + theTableName
    var rStr = ""
    var theData = [String:Any]()

    for i in 0..<columns.count {
        rStr += "&c" + "\(i)" + "=" + columns[i] +
            "&r" + "\(i)" + "=" + records[i]
    }
    recordString = tbNameStr + rStr
    print("RECORD STRING: \(recordString)")

    let requestURL = URL(string: PATH_TO_API_FOLDER + "queryWhereKeyContains.php?" + recordString)

    //create the session object
    let session = URLSession.shared

    //now create the URLRequest object using the url object
    let request = URLRequest(url: requestURL!)

    //create dataTask using the session object to send data to the server
    let task = session.dataTask(with: request as URLRequest, completionHandler: { data, response, error in

        //exiting if there is some error
        if error != nil {
            print("Error is: \(error!.localizedDescription)")
            return
        } else {

        }

        do {
            if let json = try JSONSerialization.jsonObject(with: data!, options: .mutableContainers) as? [String: Any] {
                theData = json
                print("JSON: \(json)")
            }
        } catch let error { print("ERROR IN PARSING JSON: \(error.localizedDescription)") }

    })

    task.resume()


    let flag = true
    completionHandler(flag, theData)
}

我在 ViewController.swift 中调用该函数，如下所示：

let query = NJObject(tableName: HOTEL_TABLE_NAME)
query.whereKeyContains(columnName: HOTEL_NAME, record: "Hotel")
query.findObjectInBackground { (succ, objects) in
    print("OBJECTS: \(objects)")
    print("SUCCESS: \(succ)")
}

因此，在 Xcode 控制台中，我正确地获取了我的 JSON 数据，但是在打印完成处理程序时，data（打印为 OBJECTS）为空。

OBJECTS: [:]
SUCCESS: true
JSON: ["objects": <__NSArrayM 0x17004b4c0>(
{
    address = "<null>";
    createdAt = "2017-08-12 23:08:48";
    description = "lorem ipsec dolor sit";
    email = "<null>";
},
{
    address = "<null>";
    createdAt = "2017-08-14 06:19:10";
    description = "lorem ipsec dolor sit";
    email = "<null>";
})
]

我注意到的一件事是控制台首先打印 OBJECTS 和空 [:] 和 SUCCESS 日志，然后是 JSON 数据。

所以我确定我的 findObjectInBackground() 函数有问题，我只是想不出问题出在哪里。

Answer 1

问题是您在网络请求的完成处理程序之外调用完成处理程序，因此您的函数的完成处理程序 returns 在异步网络请求之前 return。您需要将其移动到请求的完成处理程序中。

do {
    if let json = try JSONSerialization.jsonObject(with: data!, options: .mutableContainers) as? [String: Any] {
        theData = json
        print("JSON: \(json)")
        completionHandler(true, theData)
    }
}

Answer 2

您必须将完成处理程序放入数据任务的完成处理程序

可以省略URLRequest的创建，GET是默认的，直接传URL:

let task = session.dataTask(with: requestURL!, completionHandler: { data, response, error in

    //exiting if there is some error
    if error != nil {
        print("Error is: \(error!.localizedDescription)")
        completionHandler(false, [:])
        return
    } 

    do {
        if let json = try JSONSerialization.jsonObject(with: data!) as? [String: Any] {
            print("JSON: \(json)")
            completionHandler(true, json) // the variable `theData` is not needed.
        }
    } catch let error { print("ERROR IN PARSING JSON: \(error.localizedDescription)") }
      completionHandler(false, [:])
})

task.resume()

并且不要传.mutableContainers，在Swift

中没有意义

旁注：在 Swift 3 中，这个闭包声明就足够了：

typealias CompletionHandler = (Bool, [String:Any]) -> Void

iOS Swift 3 CompletionHandler 不工作

iOS Swift 3 CompletionHandler not working

json

completionhandler

swift3