swift - 为什么变量在循环内的解析查询中使用时不会改变它的值

Question

My problem is as follows: I have an argument class where all arguments have a parentId which are indeed objectId of other arguments. I would like to write a query where I can get a list of all arguments that are connected to each other with this kind of parent-child relationship. So i have tried this..

class ArgumentViewController: UIViewController {

var all = [String]()
var temporaryId = "vEKV1xCO09"

override func viewDidLoad() {
    super.viewDidLoad()
    
    for _ in 1...3 {
        let query = PFQuery(className: "Argument").whereKey("objectId", equalTo: temporaryId)
        
        query.findObjectsInBackground { (objects, error) in
            if let arguments = objects {
                for argument in arguments {
                    self.all.append(argument["parentId"] as! String)
                    print(self.all)
                    self.temporaryId = argument["parentId"] as! String
                }
            }
        }
    }

}

but the problem is temporaryId inside the loop does not update itself. It remains the same in all iterartions. Hence when i do print(self.all) i simply get an array of 3 strings which all are parent of my initial argument

My goal is to get an array that is [parent of my initial argument, parent of parent of my initial argument, parent of parent of parent of my ...]

I have searched similar topics but couldn't find a solution. Any help would be very appreciated.

Answer 1

由于 query.findObjectsInBackground 在后台线程中运行，因此无法在每个中使用新检索到的 @"parentId" 来更新 temporaryId for 循环。

所以我想你可以创建一个递归函数，例如:

func getParentId() {
    let query = PFQuery(className: "Argument").whereKey("objectId", equalTo: temporaryId)

    query.findObjectsInBackground { (objects, error) in
        if let arguments = objects {
            for argument in arguments {
                self.all.append(argument["parentId"] as! String)
                print(self.all)
                self.temporaryId = argument["parentId"] as! String
                while (all.count <= 3) {
                    getParentId()
                }
            }
        }
    }
}

作为一名 Objective-C 开发人员，我在 Swift 方面的练习还不够，所以如果我犯了一些语法错误，我很抱歉。