Apple WatchKit 扩展后台刷新示例代码
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【中文标题】Apple WatchKit 扩展后台刷新示例代码【英文标题】:Apple Sample Code for WatchKit Extension Background Refresh 【发布时间】:2017-09-07 01:30:12 【问题描述】:我一直在寻找这个问题的答案很长一段时间,所以我想我愿意冒着投反对票的风险来发布它。
基本上,我想让 Apple 提供的 Apple Watch 后台刷新示例代码真正起作用(下面的链接和代码)。
我已经在模拟器和带有 Apple Watch Series 2 的 iPhone 6s 上进行了尝试,但后台任务从未成功完成到时间更新的地步。我尝试将手表应用程序固定到扩展坞上,并且尝试将应用程序保持在前台并将其发送到后台,无论是在模拟器中还是在实际手表上。我什至试着等了将近一年,看看 Xcode 或 Apple Watch 是否会收到更新以使其正常工作。
是否有人成功修改了 Apple 提供的代码以使其正常工作?
您可以在这里下载整个可运行的示例项目:WatchBackgroundRefresh: Using WKRefreshBackgroundTask to update WatchKit apps in the background
/*
Copyright (C) 2016-2017 Apple Inc. All Rights Reserved.
See LICENSE.txt for this sample’s licensing information
Abstract:
The main interface controller.
*/
import WatchKit
import Foundation
class MainInterfaceController: WKInterfaceController, WKExtensionDelegate, URLSessionDownloadDelegate
// MARK: Properties
let sampleDownloadURL = URL(string: "http://devstreaming.apple.com/videos/wwdc/2015/802mpzd3nzovlygpbg/802/802_designing_for_apple_watch.pdf?dl=1")!
@IBOutlet var timeDisplayLabel: WKInterfaceLabel!
private let dateFormatter: DateFormatter =
let formatter = DateFormatter()
formatter.dateStyle = .none
formatter.timeStyle = .long
return formatter
()
// MARK: WKInterfaceController
override func awake(withContext context: Any?)
super.awake(withContext: context)
// Configure interface objects here.
WKExtension.shared().delegate = self
updateDateLabel()
// MARK: WKExtensionDelegate
func handle(_ backgroundTasks: Set<WKRefreshBackgroundTask>)
for task : WKRefreshBackgroundTask in backgroundTasks
print("received background task: ", task)
// only handle these while running in the background
if (WKExtension.shared().applicationState == .background)
if task is WKApplicationRefreshBackgroundTask
// this task is completed below, our app will then suspend while the download session runs
print("application task received, start URL session")
scheduleURLSession()
else if let urlTask = task as? WKURLSessionRefreshBackgroundTask
let backgroundConfigObject = URLSessionConfiguration.background(withIdentifier: urlTask.sessionIdentifier)
let backgroundSession = URLSession(configuration: backgroundConfigObject, delegate: self, delegateQueue: nil)
print("Rejoining session ", backgroundSession)
// make sure to complete all tasks, even ones you don't handle
task.setTaskCompleted()
// MARK: Snapshot and UI updating
func scheduleSnapshot()
// fire now, we're ready
let fireDate = Date()
WKExtension.shared().scheduleSnapshotRefresh(withPreferredDate: fireDate, userInfo: nil) error in
if (error == nil)
print("successfully scheduled snapshot. All background work completed.")
func updateDateLabel()
let currentDate = Date()
timeDisplayLabel.setText(dateFormatter.string(from: currentDate))
// MARK: URLSession handling
func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didFinishDownloadingTo location: URL)
print("NSURLSession finished to url: ", location)
updateDateLabel()
scheduleSnapshot()
func scheduleURLSession()
let backgroundConfigObject = URLSessionConfiguration.background(withIdentifier: NSUUID().uuidString)
backgroundConfigObject.sessionSendsLaunchEvents = true
let backgroundSession = URLSession(configuration: backgroundConfigObject)
let downloadTask = backgroundSession.downloadTask(with: sampleDownloadURL)
downloadTask.resume()
// MARK: IB actions
@IBAction func ScheduleRefreshButtonTapped()
// fire in 20 seconds
let fireDate = Date(timeIntervalSinceNow: 20.0)
// optional, any SecureCoding compliant data can be passed here
let userInfo = ["reason" : "background update"] as NSDictionary
WKExtension.shared().scheduleBackgroundRefresh(withPreferredDate: fireDate, userInfo: userInfo) (error) in
if (error == nil)
print("successfully scheduled background task, use the crown to send the app to the background and wait for handle:BackgroundTasks to fire.")
以下是在模拟器上运行时的输出。在其他配置下运行时的类似输出(但不一定完全相同):
successfully scheduled background task, use the crown to send the app to the background and wait for handle:BackgroundTasks to fire.
received background task: <WKSnapshotRefreshBackgroundTask: 0x7b019030>
received background task: <WKApplicationRefreshBackgroundTask: 0x7a711290>
application task received, start URL session
【问题讨论】:
一些一般性建议:使用 Swift 命名约定,函数名称使用小写字母 (scheduleRefreshButtonTapped()
)。关于您的问题:请提供更多关于什么不起作用的上下文。调度成功了吗? handle(backgroundTasks:
) 有没有被调用过?请更具体。
@DávidPásztor 谢谢,当我将任何可用的 Apple 代码合并到我自己的项目中时,我一定会修正命名约定。至于不起作用的细节,我已经编辑了问题以添加相应输出的示例。
您是否在连接真 iPhone 的手表模拟器或连接 iPhone 的真 Apple Watch 上尝试过此代码。
@AasimKhan 谢谢,是的,我有。
此演示的 Apple 示例代码已被删除。谁有副本的链接。我能找到的最接近的是 Microsoft-Xamarin 转换:docs.microsoft.com/en-us/xamarin/ios/watchos/platform/…
【参考方案1】:
对于可能发现此问题的任何人,我看到了 2 个问题,都与 URLSession 调度有关。通过这些更改,我认为 Apple 示例代码实际上可以工作,至少在模拟器上是这样。
-sampleDownloadURL
需要安全,因此需要使用 HTTPS 的 URL。这个有效:https://api.weather.gov/points/42.3584,-71.0598/forecast
-在我看来,URLSession
的代表从未设置为 self
,因此以下更改修复了该问题:
let backgroundSession = URLSession(configuration: backgroundConfigObject, delegate: self, delegateQueue: nil)
以下工作(虽然不太完整)代码非常有帮助:What's New in watchOS 3: Background Tasks
编辑:可能出现的另一个问题是任务在收到后立即完成。在实践中,它们应该被保存(例如,在局部变量中),然后在该任务的所有处理完成后完成。对于这段代码,我认为这意味着挂在WKApplicationRefreshBackgroundTask
上,直到调用scheduleSnapshot
之后才调用setTaskCompleted()
。
【讨论】:
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