解析查询结果，不附加到新数组。

I'm using Swift and I'm trying to append a Parse Query's results to an array, however, the array only shows the appended value when it's printed within the query's for loop. When I try printing the array outside of the loop before the method's return, I get an empty array. How can I get the array with the appended value to show outside of the for loop?

我正在使用Swift，并试图将解析查询的结果追加到一个数组中，但是，该数组只显示在查询的for循环中打印时附加的值。当我尝试在方法返回之前在循环外打印数组时，我得到一个空数组。如何使用append值来显示for循环之外的数组?

class Task {   

    func all() -> Array<String> {
        var taskArray = Array<String>()
        var query = PFQuery(className:"Task")
        var currentUser = PFUser.currentUser() // this will now be nil
        let userId = currentUser?.objectId
        query.whereKey("userId", equalTo: currentUser!)
        query.findObjectsInBackgroundWithBlock {
            (objects: [AnyObject]?, error: NSError?) -> Void in

            if error == nil {
                // The find succeeded.
                println("Successfully retrieved \(objects!.count) tasks.")

                // Do something with the found objects
                if let objects = objects as? [PFObject] {
                    for object in objects {
//                        println(object.objectId)
                        let title = object["title"]! as! String
                        taskArray.append(title)
                        println("Array: \(taskArray)")
                    }
                }
            } else {
                // Log details of the failure
                println("Error: \(error!) \(error!.userInfo!)")
            }
        }
        println("Outside query array: \(taskArray)")


        return taskArray
    }
}

It looks like the outside query is being called before the query or something along the lines of that. Debug console:

它看起来就像在查询之前调用外部查询或类似的东西。调试控制台:

1 个解决方案

#1

As you said, the println("Outside query array: \(taskArray)") is called before println("Array: \(taskArray)") and there is a simple explanation to this.

正如您所说的，println(“外部查询数组:\(taskArray)”)在println(“数组:\(taskArray)”)之前被调用，这里有一个简单的解释。

findObjectsInBackgroundWithBlock is an asynchronous method, which means that it starts another thread and works on this one. This means that the moment you call findObjectsInBackgroundWithBlock, then it continues directly to println("Outside query array: \(taskArray)").

findObjectsInBackgroundWithBlock是一个异步方法，这意味着它启动另一个线程并在这个线程上工作。这意味着当您调用findObjectsInBackgroundWithBlock时，它会继续直接到println(“外部查询数组:\(taskArray)”)。

Now, it is possible to download stuff from Parse synchronously (so it will not skip directly to println("Outside query array: \(taskArray)")), but I will not recommend you to do this.

现在，可以同步地下载解析的内容(因此它不会直接跳转到println(“外部查询数组:\(taskArray)”)，但是我不会建议您这样做。

Instead I will recommend that you implement a closure which is called when the download is finished. Something similar to the following (PS, it's been written in Swift 2):

相反，我建议您实现一个闭包，在下载完成时调用该闭包。类似如下(PS，它是在Swift 2中写的):

//
//  ViewController.swift
//  ParseFun
//
//  Created by Stefan Veis Pennerup on 21/09/15.
//  Copyright (c) 2015 Kumuluzz. All rights reserved.
//

import UIKit

class ViewController: UIViewController {

    // MARK: - Lifecycle methods

    override func viewDidLoad() {
        super.viewDidLoad()

        all { (tasks) -> Void in
            print("The downloaded tasks are: \(tasks)")
        }
    }

    // MARK: - Download methods

    func all(completionHandler: ([String])->Void) {
        // Creates the query
        var taskArray = Array<String>()
        let query = PFQuery(className:"Task")
        let currentUser = PFUser.currentUser() // this will now be nil
        query.whereKey("userId", equalTo: currentUser!)

        // Starts the download
        query.findObjectsInBackgroundWithBlock {
            (objects: [AnyObject]?, error: NSError?) -> Void in

            if error == nil {
                // The find succeeded.
                print("Successfully retrieved \(objects!.count) tasks.")

                // Do something with the found objects
                if let objects = objects as? [PFObject] {
                    for object in objects {
                        let title = object["title"]! as! String
                        taskArray.append(title)
                        print("Array: \(taskArray)")
                    }
                }

                completionHandler(taskArray)

            } else {
                // Log details of the failure
                print("Error: \(error!) \(error!.userInfo)")
            }
        }
    }
}

#1