如何在循环中快速保存在后台

Question

我将数据作为数组存储在 NSUserDefaults 中。我需要使用 Parse Server 获取这些数据并将其存储在数据库中。当我尝试遍历数组并使用 saveInBackgroundWithBlock 时，循环再次运行，在块完成之前设置新值。将此数据作为单个对象保存在数据库中的最佳方法是什么？

let other = PFObject(className: "Other")
if (NSUserDefaults.standardUserDefaults().objectForKey("otherTypes") != nil) && (NSUserDefaults.standardUserDefaults().objectForKey("otherCosts") != nil) {
        otherCosts = NSUserDefaults.standardUserDefaults().objectForKey("otherCosts") as! [Double]

        otherTypes = NSUserDefaults.standardUserDefaults().objectForKey("otherTypes") as! [String]

        for costs in otherCosts {

            other.setObject(PFUser.currentUser()!.objectId!, forKey: "userId")
            other.setObject(otherTypes[i], forKey: "otherName")
            let cost = String(costs)
            other.setObject(cost, forKey: "otherCost")
            i = i + 1
            other.saveInBackgroundWithBlock({ (success, error) -> Void in
                if error == nil {
                    print("Success")
                    NSUserDefaults.standardUserDefaults().setObject(nil, forKey: "otherTypes")
                    NSUserDefaults.standardUserDefaults().setObject(nil, forKey: "otherCosts")
                } else {
                    print("Fail")
                }
            })
        } 

Answer 1

您需要在 for 循环中分配PFObject inside，否则您只是一遍又一遍地处理同一个对象。

if (NSUserDefaults.standardUserDefaults().objectForKey("otherTypes") != nil) && (NSUserDefaults.standardUserDefaults().objectForKey("otherCosts") != nil) {
        otherCosts = NSUserDefaults.standardUserDefaults().objectForKey("otherCosts") as! [Double]

        otherTypes = NSUserDefaults.standardUserDefaults().objectForKey("otherTypes") as! [String]

        for costs in otherCosts {
            let other = PFObject(className: "Other")
            other.setObject(PFUser.currentUser()!, forKey: "userId")
            other.setObject(otherTypes[i], forKey: "otherName")
            let cost = String(costs)
            other.setObject(cost, forKey: "otherCost")
            i = i + 1
            other.saveInBackgroundWithBlock({ (success, error) -> Void in
                if error == nil {
                    print("Success")
                    NSUserDefaults.standardUserDefaults().setObject(nil, forKey: "otherTypes")
                    NSUserDefaults.standardUserDefaults().setObject(nil, forKey: "otherCosts")
                } else {
                    print("Fail")
                }
            })
        }

作为

Answer 2

您可以在后台线程上运行所有这些并使用信号量进行阻塞：

let semaphore = dispatch_semaphore_create(0)
for costs in otherCosts {
    //...
    other.saveInBackgroundWithBlock({ (success, error) -> Void in
        // ...
        dispatch_semaphore_signal(semaphore)
    })
    dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER)
}

请注意，由于这是一个长时间运行的操作，您绝对不希望在前台线程中执行此保存操作。

另一种可能性是将整个事情转换为工作队列排列，如下所示：

func tryToSend() {
    let defaults = NSUserDefaults.standardUserDefaults()
    if let otherTypes = defaults.objectForKey("otherTypes") as? [String],
        let otherCosts = defaults.objectForKey("otherCosts") as? [Double] {
            if otherTypes.count > 0 {
                let other = PFObject(className: "Other")
                other.setObject(PFUser.currentUser()!.objectId!, forKey: "userId")
                other.setObject(otherTypes[0], forKey:"otherName")
                other.setObject("\(otherCosts[0])", forKey:"otherCost")
                other.saveInBackgroundWithBlock({ (success, error) -> Void in
                    if error == nil {
                        print("Success")
                        otherTypes = otherTypes[1..<otherTypes.count]
                        otherCosts = otherCosts[1..<otherCosts.count]
                        defaults.setObject(otherTypes, forKey: "otherTypes")
                        defaults.setObject(otherCosts, forKey: "otherCosts")
                        tryToSend()
                    } else {
                        print("Fail")
                    }
                })
            }
    }
}

这样做的好处是您不必担心分离另一个线程，并且您可以动态地向 otherTypes 和 otherCosts 添加更多条目（通过适当的同步以确保 NSUserDefaults 在读取时不会被修改）

在这种情况下，最后一个想法是使用PFObject.saveAllInBackground 方法在一个网络操作中完成整个操作，如下所示：

let defaults = NSUserDefaults.standardUserDefaults()
if let otherTypes = defaults.objectForKey("otherTypes") as? [String],
    let otherCosts = defaults.objectForKey("otherCosts") as? [Double] {
        let others = zip(otherTypes, otherCosts).map { type, cost in
            let other = PFObject(className:"Other")
            other.setObject(PFUser.currentUser()!.objectId!, forKey: "userId")
            other.setObject(type, forKey: "otherName")
            other.setObject("\(cost)", forKey: "otherCost")
            return other
        }

        PFObject.saveAllInBackground(others) { (success, error) in
            if error == nil {
                print("Success")
                NSUserDefaults.standardUserDefaults().setObject(nil, forKey: "otherTypes")
                NSUserDefaults.standardUserDefaults().setObject(nil, forKey: "otherCosts")
            } else {
                print("Fail")
            }
        }
}