c# - Xamarin 表格 : Check if user inactive after some time log out app

Question

您好，我正在尝试使用 PCL 以 xamarin 形式构建应用程序。如果应用程序空闲时间超过 10 分钟或更长时间，我将尝试从我的应用程序中注销用户。我通过应用程序即将进入休眠状态时调用的事件进行了尝试。但是，如果设备屏幕超时设置为永不超时，那么它可能永远不会进入休眠状态。那么我该如何实现呢。我是 xamarin 表单的新手。当我为所有平台构建应用程序时，我很困惑如何管理此超时？

Answer 1

现在我使用以下方法。可能需要做一些额外的测试以确保一切都按预期工作。例如，我不确定如果应用程序(iOS 或 Android)在后台长时间运行会发生什么。计时器是否仍会每秒调用一次？也许当使用到期时间足够短(~5 分钟)的计时器时，这根本不是问题？等等……

我的方法基于我在网上找到的几段代码(一些 Xamarin 代码，一些 Swift/Java 代码)——似乎没有一个很好的综合解决方案。

无论如何，一些初步测试表明这种方法工作正常。

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首先，我创建了一个名为 SessionManager 的单例类。此类包含一个计时器(实际上只是一个每秒休眠的 while 循环)和启动、停止和延长计时器的方法。如果 session 到期计时器到期，它也会触发一个事件。

public sealed class SessionManager
{
    static readonly Lazy<SessionManager> lazy =
        new Lazy<SessionManager>(() => new SessionManager());

    public static SessionManager Instance { get { return lazy.Value; } }

    SessionManager() { 
        this.SessionDuration = TimeSpan.FromMinutes(5);
        this.sessionExpirationTime = DateTime.FromFileTimeUtc(0);
    }

    /// <summary>
    /// The duration of the session, by default this is set to 5 minutes.
    /// </summary>
    public TimeSpan SessionDuration;

    /// <summary>
    /// The OnSessionExpired event is fired when the session timer expires.
    /// This event is not fired if the timer is stopped manually using 
    /// EndTrackSession.
    /// </summary>
    public EventHandler OnSessionExpired;

    /// <summary>
    /// The session expiration time.
    /// </summary>
    DateTime sessionExpirationTime;

    /// <summary>
    /// A boolean value indicating wheter a session is currently active.
    /// Is set to true when StartTrackSessionAsync is called. Becomes false if 
    /// the session is expired manually or by expiration of the session 
    /// timer.
    /// </summary>
    public bool IsSessionActive { private set; get; }

    /// <summary>
    /// Starts the session timer.
    /// </summary>
    /// <returns>The track session async.</returns>
    public async Task StartTrackSessionAsync() {
        this.IsSessionActive = true;

        ExtendSession();

        await StartSessionTimerAsync();
    }

    /// <summary>
    /// Stop tracking a session manually. The OnSessionExpired will not be 
    /// called.
    /// </summary>
    public void EndTrackSession() {
        this.IsSessionActive = false;

        this.sessionExpirationTime = DateTime.FromFileTimeUtc(0);
    }

    /// <summary>
    /// If the session is active, then the session time is extended based 
    /// on the current time and the SessionDuration.
    /// duration.
    /// </summary>
    public void ExtendSession()
    {
        if (this.IsSessionActive == false) {
            return;
        }

        this.sessionExpirationTime = DateTime.Now.Add(this.SessionDuration);
    }

    /// <summary>
    /// Starts the session timer. When the session is expired and still 
    /// active the OnSessionExpired event is fired. 
    /// </summary>
    /// <returns>The session timer async.</returns>
    async Task StartSessionTimerAsync() {
        if (this.IsSessionActive == false) {
            return;
        }

        while (DateTime.Now < this.sessionExpirationTime) {
            await Task.Delay(1000);                
        }

        if (this.IsSessionActive && this.OnSessionExpired != null) {
            this.IsSessionActive = false;

            this.OnSessionExpired.Invoke(this, null);
        }
    }
}

然后，对于 Android 应用程序，我:

• 在 MainActivity 中配置 SessionManager 以在 session 过期时注销。

• 覆盖 MainActivity 中的 OnUserInteraction 方法以延长用户交互的 session 计时器。

  public class MainActivity /* ... */ {
      protected override void OnCreate(Bundle bundle)
      {   
          // ...
  
          SessionManager.Instance.SessionDuration = TimeSpan.FromSeconds(10);
          SessionManager.Instance.OnSessionExpired = HandleSessionExpired;
      }
  
      public override void OnUserInteraction()
      {
          base.OnUserInteraction();
  
          SessionManager.Instance.ExtendSession();
      }
  
      async void HandleSessionExpired(object sender, EventArgs e)
      {
          await App.Instance.DoLogoutAsync();
      }    
  }
  

对于 iOS，我执行以下操作:

• 在 AppDelegate 中配置 SessionManager 以在 session 过期时注销。

• 将自定义手势处理程序添加到键窗口以延长用户交互的 session 计时器。

  public partial class AppDelegate /* ... */
  {
      public override bool FinishedLaunching(UIApplication app, NSDictionary options)
      {
          // ...
  
          var success = base.FinishedLaunching(app, options);
  
          if (success) {
              SessionManager.Instance.SessionDuration = TimeSpan.FromSeconds(10);
              SessionManager.Instance.OnSessionExpired += HandleSessionExpired;
  
              var allGesturesRecognizer = new AllGesturesRecognizer(delegate
              {
                  SessionManager.Instance.ExtendSession();
              });
  
              this.Window.AddGestureRecognizer(allGesturesRecognizer);
          }
  
          return success;
      }
  
      async void HandleSessionExpired(object sender, EventArgs e)
      {
          await App.instance.DoLogoutAsync();
      }
  
      class AllGesturesRecognizer: UIGestureRecognizer {
          public delegate void OnTouchesEnded();
  
          private OnTouchesEnded touchesEndedDelegate;
  
          public AllGesturesRecognizer(OnTouchesEnded touchesEnded) {
              this.touchesEndedDelegate = touchesEnded;
          }
  
          public override void TouchesEnded(NSSet touches, UIEvent evt)
          {
              this.State = UIGestureRecognizerState.Failed;
  
              this.touchesEndedDelegate();
  
              base.TouchesEnded(touches, evt);
          }
      }
  }
  

---

编辑: Bolo 在下面提出了一个很好的问题，所以我将其添加到这里。一旦用户登录，就会调用 StartTrackSessionAsync。当然，当用户注销应用程序时，也应该调用 EndTrackSession。