使用 Parse 在 PFQuery 之外重新调整空白数组的数组. [英] Array retuning a blank array outside of PFQuery with Parse.

问题描述

数组在 PFQuery 之外返回空数组.出于某种原因，项目在编译时没有被传递到数组.

Array returning a blank array when outside of the PFQuery. For some reason, the items are not being passed to the array when compiled.

class DriverViewController: UIViewController {
var placesArr : Array<Place> = []


    override func viewDidLoad() {
    super.viewDidLoad()
    self.window = UIWindow(frame: UIScreen.mainScreen().bounds)


    var query = PFQuery(className:"places")
    query.whereKey("username", equalTo:"[e-mail]")
    query.findObjectsInBackgroundWithBlock {
        (objects: [AnyObject]?, error: NSError?) -> Void in

        if error == nil {
            println("Successfully retrieved (objects!.count) scores.")

            if let objects = objects as? [PFObject] {
                for object in objects {
             let x = Place(aIdent: (object["Ident"] as! Int), aName: (object["name"] as! String), aAddress: (object["originAddress"] as! String), aCity: (object["originCity"] as! String), aCategoryName: (object["catName"] as! String), aLat: (object["aLat"] as! String), aLng: (object["aLng"] as! String))

                    self.placesArr.append(x)
                    println(placesArr) //****It works here and prints an array****
                }
            }
        } else {
            // Log details of the failure
            println("Error: (error!) (error!.userInfo!)")
        }
    }
 println(placesArr) //****But here it returns a blank array and this is where I need it to return an array****

推荐答案

这是一个非常常见的与线程相关的误解，问题是事件运行的顺序:

This a very common misunderstanding relating to threading, the issue is what order events run:

// Runs 1st
query.findObjectsInBackgroundWithBlock {
    (objects: [AnyObject]?, error: NSError?) -> Void in
    // Runs 3rd
}
// Runs 2nd
println(placesArr)

当您调用 findObjectsInBackground 时，程序的执行不会停止，它会查找对象:inBackground 这意味着繁重的网络请求被分派到不同的队列，以便用户仍然可以与屏幕交互.一个简单的方法是这样做:

The execution of the program doesn't halt when you call findObjectsInBackground, it finds objects: inBackground which means the heavy lifting of a network request is dispatched to a different queue so that the user can still interact with the screen. A simple way to do this would be to do:

var placesArray: [Place] = [] {
    didSet {
        // Do any execution that needs to wait for places array here.
    }
}

您还可以在解析响应块中触发后续操作，我个人认为依赖于在 didSet 中执行的属性更新的执行行为是一种控制流程的好方法.

You can also trigger subsequent actions within the parse response block, I just personally find executing behavior dependent on a property update being executed in didSet to be a nice way to control flow.

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