iOS applicationWillResignActive 任​​务在应用程序再次激活之前不会执行

Question

我正在尝试使用 applicationWillResignActive() 以便在应用程序进入后台之前将一些数据同步到我的 Firestore 数据库。

func applicationWillResignActive(_ application: UIApplication) {
        self.uploadWantToPlay()
}

当我从 applicationWillResignActive() 调用我的上传功能时，它 运行 但是在下一次应用程序激活之前没有数据添加到 Firestore。

当我出于测试目的而不是 运行 我的 ViewControllers 之一的相同功能时，数据会立即添加到 Firestore。

我也试过从 applicationDidEnterBackground() 调用该函数，我试过 运行 在它自己的 DispatchQueue 中调用它。但它有相同的结果。

当用户即将离开应用程序并让它正确执行数据库同步时，我如何运行此功能？

处理数据库同步的函数；

func uploadWantToPlay() {
    print ("Inside uploadWantToPlay")
    if let wantToPlay = User.active.wantToPlayList {
        if let listEntries = wantToPlay.list_entries {
            let cleanedEntries = listEntries.compactMap({ (entry: ListEntry) -> ListEntry? in
                if entry.game?.first_release_date != nil {
                    return entry
                } else {
                    return nil
                }
            })
            let gamesToUpload = cleanedEntries.filter {
                [=12=].game!.first_release_date! > Int64(NSDate().timeIntervalSince1970 * 1000)
            }
            DatabaseConnection().writeWantToPlayToDatabase(user: User.active,wantToPlay: gamesToUpload)
        }
    }
}

func writeWantToPlayToDatabase(user: User, wantToPlay: [ListEntry]) {
    firebaseSignIn()
    let deviceId = ["\(user.deviceId)": "Device ID"]
    for entry in wantToPlay {
        let wantToPlayGameRef = fireStore.collection(WANTTOPLAY).document("\(entry.game!.id!)")

        wantToPlayGameRef.updateData(deviceId) {(err) in
            if err != nil {
                wantToPlayGameRef.setData(deviceId) {(err) in
                    if let err = err {
                        Events().logException(withError: err, withMsg: "DatabaseConnection-writeWantToPlayToDatabase(user, [ListEntry]) Failed to write to database")
                    } else {
                        print("Document successfully written to WantToPlayGames")
                    }
                }
            } else {
                print("Document successfully updated in WantToPlayGames")
            }
        }
    }
}

Answer 1

根据Apple documentation

Apps moving to the background are expected to put themselves into a quiescent state as quickly as possible so that they can be suspended by the system. If your app is in the middle of a task and needs a little extra time to complete that task, it can call the beginBackgroundTaskWithName:expirationHandler: or beginBackgroundTaskWithExpirationHandler: method of the UIApplication object to request some additional execution time. Calling either of these methods delays the suspension of your app temporarily, giving it a little extra time to finish its work. Upon completion of that work, your app must call the endBackgroundTask: method to let the system know that it is finished and can be suspended.

所以，您在这里需要做的是在您的应用暂停时执行一个有限长度的任务。这将为您的应用赢得足够的时间将您的记录同步到服务器。

示例片段：

import UIKit

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?
    var backgroundTask: UIBackgroundTaskIdentifier!

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
        // Override point for customization after application launch.
        return true
    }

    func applicationWillResignActive(_ application: UIApplication) {
        self.registerBackgroundTask()

        // Do your background work here
        print("Do your background work here")

        // end the task when work is completed
        self.endBackgroundTask()
    }

    func registerBackgroundTask() {
        self.backgroundTask = UIApplication.shared.beginBackgroundTask { [weak self] in
            self?.endBackgroundTask()
        }
        assert(self.backgroundTask != UIBackgroundTaskInvalid)
    }

    func endBackgroundTask() {
        print("Background task ended.")
        UIApplication.shared.endBackgroundTask(backgroundTask)
        backgroundTask = UIBackgroundTaskInvalid
    }

}

有关详细信息，请参阅此 article。