扩展执行似乎在 Windows 10 通用 JavaScript 应用程序中不起作用

Question

我有一个用 JavaScript 编写的 Windows 10 通用应用程序。该应用程序是一个位置跟踪器，需要在后台运行，我正在尝试使用 ExtendedExecution API 来实现这一点。不过，我发现这在 C#/XAML 应用程序中可以正常工作，但在 JavaScript 应用程序中不起作用。

作为一项实验，在 Visual Studio 2015 中，我通过创建了一个新的 C# 项目File -> New -> Project -> Visual C# -> Blank App (Universal Windows)并按如下方式对其进行了组装：

/// <summary>
/// An empty page that can be used on its own or navigated to within a Frame.
/// </summary>
public sealed partial class MainPage : Page
{
    private Geolocator locator;
    private ObservableCollection<string> coordinates = new ObservableCollection<string>();
    private ExtendedExecutionSession session;

    public MainPage()
    {
        this.InitializeComponent();

        // Start geo locating
        locator = new Geolocator();
        locator.DesiredAccuracy = PositionAccuracy.High;
        locator.DesiredAccuracyInMeters = 0;
        locator.MovementThreshold = 0;
        locator.PositionChanged += positionChanged;
        coords.ItemsSource = coordinates;

        // Request extended execution
        RequestExtendedExecution();
    }

    private async void RequestExtendedExecution()
    {

        // Request extended execution via the ExtendedExecution API
        session = new ExtendedExecutionSession();
        session.Description = "Location Tracker";
        session.Reason = ExtendedExecutionReason.LocationTracking;
        session.Revoked += ExtendedExecutionSession_Revoked;
        var result = await session.RequestExtensionAsync();
        if (result == ExtendedExecutionResult.Allowed)
            coordinates.Insert(0, "Extended execution SUCCESS");
        else if (result == ExtendedExecutionResult.Denied)
            coordinates.Insert(0, "Extended execution DENIED");
        else
            coordinates.Insert(0, "Extended execution unexpected return code");
    }

    private async void EndExtendedExecution()
    {
        if (session != null)
        {
            session.Dispose();
            session = null;
        }
    }

    private void ExtendedExecutionSession_Revoked(object sender, ExtendedExecutionRevokedEventArgs args)
    {
        var _ = Dispatcher.RunAsync(Windows.UI.Core.CoreDispatcherPriority.Normal, () =>
        {
            coordinates.Insert(0, "Extended execution REVOKED: " + ((args.Reason == ExtendedExecutionRevokedReason.Resumed) ? "Resumed" : (args.Reason == ExtendedExecutionRevokedReason.SystemPolicy) ? "Resources" : "Unknown reason"));
        });
        EndExtendedExecution();
    }

    private void positionChanged(Geolocator sender, PositionChangedEventArgs args)
    {
        var coord = args.Position;
        string position = string.Format("{0},{1}",
            args.Position.Coordinate.Point.Position.Latitude,
            args.Position.Coordinate.Point.Position.Longitude);
        var _ = Dispatcher.RunAsync(Windows.UI.Core.CoreDispatcherPriority.Normal, () =>
        {
            coordinates.Insert(0, position);
        });
    }
}

标记很简单：

<ListView x:Name="coords" />

这绝对按预期工作。当我请求扩展会话时，我得到“扩展执行成功”，当最小化时，应用程序继续向 ListView 添加坐标，当返回到前台时，我得到“扩展执行撤销：恢复”。超级骗子。回到 Visual Studio 2015，然后我通过创建一个新的 JavaScript 项目File -> New -> Project -> JavaScript -> Blank App (Universal Windows)并实现了相同的功能，如下所示：

(function () {
    "use strict";

    var app = WinJS.Application;
    var activation = Windows.ApplicationModel.Activation;
    var extendedExecution = Windows.ApplicationModel.ExtendedExecution;
    var session = null;
    var geolocator = null;

    app.onactivated = function (args) {
        if (args.detail.kind === activation.ActivationKind.launch) {
            if (args.detail.previousExecutionState !== activation.ApplicationExecutionState.terminated) {

                // TODO: This application has been newly launched. Initialize your application here.

                // Start geo tracking
                Windows.Devices.Geolocation.Geolocator.requestAccessAsync().done(
                    function (accessStatus) {
                        switch (accessStatus) {
                            case Windows.Devices.Geolocation.GeolocationAccessStatus.allowed:
                                geolocator = new Windows.Devices.Geolocation.Geolocator();
                                geolocator.ReportInterval = 1000;

                                // Subscribe to PositionChanged event to get updated tracking positions
                                geolocator.addEventListener("positionchanged", function (e) {
                                    var coord = e.position.coordinate;
                                    log("app.onactivated: coord = " + coord.point.position.latitude + ", " + coord.point.position.longitude, false, true, false);
                                });
                                break;

                            case Windows.Devices.Geolocation.GeolocationAccessStatus.denied:
                                log("Geolocator.requestAccessAsync: Access to location is denied.", false, true, false);
                                break;

                            case Windows.Devices.Geolocation.GeolocationAccessStatus.unspecified:
                                log("Geolocator.requestAccessAsync: Unspecified error.", false, true, false);
                                break;
                        }
                    },
                    function (err) {
                        log("Geolocator.requestAccessAsync: error " + err, false, true, false);
                    }
                );

                // Request extended execution
                requestExtendedExecution();

            } else {
                // TODO: This application was suspended and then terminated.
                // To create a smooth user experience, restore application state here so that it looks like the app never stopped running.
            }
            args.setPromise(WinJS.UI.processAll());
        }
    };

    app.oncheckpoint = function (args) {
        // TODO: This application is about to be suspended. Save any state that needs to persist across suspensions here.
        // You might use the WinJS.Application.sessionState object, which is automatically saved and restored across suspension.
        // If you need to complete an asynchronous operation before your application is suspended, call args.setPromise().
        log("app.oncheckpoint: application is about to be suspended");
    };

    function requestExtendedExecution() {

        // If we already have an extended session, close it before requesting a new one.
        if (session != null) {
            session.close();
            session = null;
        }

        // Request extended execution via the ExtendedExecution API
        session = new extendedExecution.ExtendedExecutionSession();
        session.description = "Background location tracking";
        session.reason = extendedExecution.ExtendedExecutionReason.locationTracking;
        session.onrevoked = function (args) {
            log("requestExtendedExecution: Background mode revoked: " + args.reason);
            requestExtendedExecution();
        };
        session.requestExtensionAsync().done(
            function success() {
                log("requestExtendedExecution: Successfully enabled background mode");
            },
            function error(error) {
                log("requestExtendedExecution: Could not enable background mode: " + error);
            }
        );      
    }

    function log (text) {
        var now = new Date();
        var timestamp = now.toLocaleDateString() + " " + now.toLocaleTimeString();
        var outputDiv = document.getElementById("divOutput");
        outputDiv.innerHTML = timestamp + " " + text + "<br/>" + outputDiv.innerHTML;
    }

    app.start();
})();

标记是：

<div id="divOutput"></div>

当我请求扩展会话时，我仍然得到“扩展执行成功”，是的，但是当我最小化应用程序时，app.oncheckpoint 被调用，应用程序被暂停并且没有进一步的活动，直到它返回到前台。我也尝试从 app.oncheckpoint 中请求扩展会话，但这也没有效果。

有人对此有所了解吗？提前致谢。

Answer 1

有用。实际问题是您的代码不侦听 revoke 事件。应该撤销。:)

并且您的代码中存在一些小问题。

请尝试以下操作：

function requestExtendedExecution() {

    // Request extended execution via the ExtendedExecution API
    session = new extendedExecution.ExtendedExecutionSession();
    session.description = "Background location tracking";
    session.reason = extendedExecution.ExtendedExecutionReason.locationTracking;
    session.onrevoked = function (args) {
        log("requestExtendedExecution: Background mode revoked: " + args.reason);
    };
    session.requestExtensionAsync().done(
        function success() {
            log("requestExtendedExecution: Successfully enabled background mode");
        },
        function error(error) {
            log("requestExtendedExecution: Could not enable background mode: " + error);
        }
    );
}