我试图实现后台获取，希望可以不时唤醒应用程序。

我做了这些:

      func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
application.setMinimumBackgroundFetchInterval(UIApplicationBackgroundFetchIntervalMinimum)
        return true
      }

func application(_ application: UIApplication, performFetchWithCompletionHandler completionHandler: @escaping (UIBackgroundFetchResult) -> Void) {
    debugPrint("performFetchWithCompletionHandler")
    getData()
    completionHandler(UIBackgroundFetchResult.newData)
  }

  func getData(){
    debugPrint("getData")
  }

最佳答案

您已经完成了许多必要的步骤:

// AppDelegate.swift

import UIKit
import UserNotifications
import os.log

@UIApplicationMain
class AppDelegate: UIResponder {

    var window: UIWindow?

    /// The URLRequest for seeing if there is data to fetch.

    fileprivate var fetchRequest: URLRequest {
        // create this however appropriate for your app
        var request: URLRequest = ...
        return request
    }

    /// A `OSLog` with my subsystem, so I can focus on my log statements and not those triggered 
    /// by iOS internal subsystems. This isn't necessary (you can omit the `log` parameter to `os_log`,
    /// but it just becomes harder to filter Console for only those log statements this app issued).

    fileprivate let log = OSLog(subsystem: Bundle.main.bundleIdentifier!, category: "log")

}

// MARK: - UIApplicationDelegate

extension AppDelegate: UIApplicationDelegate {

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {

        // turn on background fetch

        application.setMinimumBackgroundFetchInterval(UIApplicationBackgroundFetchIntervalMinimum)

        // issue log statement that app launched

        os_log("didFinishLaunching", log: log)

        // turn on user notifications if you want them

        UNUserNotificationCenter.current().delegate = self

        return true
    }

    func applicationWillEnterForeground(_ application: UIApplication) {
        os_log("applicationWillEnterForeground", log: log)
    }

    func application(_ application: UIApplication, performFetchWithCompletionHandler completionHandler: @escaping (UIBackgroundFetchResult) -> Void) {
        os_log("performFetchWithCompletionHandler", log: log)
        processRequest(completionHandler: completionHandler)
    }

}

// MARK: - UNUserNotificationCenterDelegate

extension AppDelegate: UNUserNotificationCenterDelegate {

    func userNotificationCenter(_ center: UNUserNotificationCenter, willPresent notification: UNNotification, withCompletionHandler completionHandler: @escaping (UNNotificationPresentationOptions) -> Void) {
        os_log("willPresent %{public}@", log: log, notification)
        completionHandler(.alert)
    }

    func userNotificationCenter(_ center: UNUserNotificationCenter, didReceive response: UNNotificationResponse, withCompletionHandler completionHandler: @escaping () -> Void) {
        os_log("didReceive %{public}@", log: log, response)
        completionHandler()
    }
}

// MARK: - Various utility methods

extension AppDelegate {

    /// Issue and process request to see if data is available
    ///
    /// - Parameters:
    ///   - prefix: Some string prefix so I know where request came from (i.e. from ViewController or from background fetch; we'll use this solely for logging purposes.
    ///   - completionHandler: If background fetch, this is the handler passed to us by`performFetchWithCompletionHandler`.

    func processRequest(completionHandler: ((UIBackgroundFetchResult) -> Void)? = nil) {
        let task = URLSession.shared.dataTask(with: fetchRequest) { data, response, error in

            // since I have so many paths execution, I'll `defer` this so it captures all of them

            var result = UIBackgroundFetchResult.failed
            var message = "Unknown"

            defer {
                self.postNotification(message)
                completionHandler?(result)
            }

            // handle network errors

            guard let data = data, error == nil else {
                message = "Network error: \(error?.localizedDescription ?? "Unknown error")"
                return
            }

            // my web service returns JSON with key of `success` if there's data to fetch, so check for that

            guard
                let json = try? JSONSerialization.jsonObject(with: data),
                let dictionary = json as? [String: Any],
                let success = dictionary["success"] as? Bool else {
                    message = "JSON parsing failed"
                    return
            }

            // report back whether there is data to fetch or not

            if success {
                result = .newData
                message = "New Data"
            } else {
                result = .noData
                message = "No Data"
            }
        }
        task.resume()
    }

    /// Post notification if app is running in the background.
    ///
    /// - Parameters:
    ///
    ///   - message:           `String` message to be posted.

    func postNotification(_ message: String) {

        // if background fetch, let the user know that there's data for them

        let content = UNMutableNotificationContent()
        content.title = "MyApp"
        content.body = message
        let trigger = UNTimeIntervalNotificationTrigger(timeInterval: 1, repeats: false)
        let notification = UNNotificationRequest(identifier: "timer", content: content, trigger: trigger)
        UNUserNotificationCenter.current().add(notification)

        // for debugging purposes, log message to console

        os_log("%{public}@", log: self.log, message)  // need `public` for strings in order to see them in console ... don't log anything private here like user authentication details or the like
    }

}

import UIKit
import UserNotifications

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        // request authorization to perform user notifications

        UNUserNotificationCenter.current().requestAuthorization(options: [.sound, .alert]) { granted, error in
            if !granted {
                DispatchQueue.main.async {
                    let alert = UIAlertController(title: nil, message: "Need notification", preferredStyle: .alert)
                    alert.addAction(UIAlertAction(title: "OK", style: .default, handler: nil))
                    self.present(alert, animated: true, completion: nil)
                }
            }
        }

        // you actually have to do some request at some point for background fetch to be turned on;
        // you'd do something meaningful here, but I'm just going to do some random request...

        let url = URL(string: "http://example.com")!
        let request = URLRequest(url: url)
        let task = URLSession.shared.dataTask(with: request) { data, response, error in
            DispatchQueue.main.async {
                let alert = UIAlertController(title: nil, message: error?.localizedDescription ?? "Sample request finished", preferredStyle: .alert)
                alert.addAction(UIAlertAction(title: "OK", style: .default, handler: nil))
                self.present(alert, animated: true)
            }
        }
        task.resume()
    }

}

关于iOS10 后台获取，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/44313278/