Question

在我的应用程序中的页面导航期间，我在系统托盘中向用户显示一条消息以及进度条以指示正在进行的操作。

我遇到的问题是在调试期间我随机收到以下错误：

{System.NullReferenceException: Object reference not set to an instance of an object.
at ContosoSocial.SetProgressIndicator.<>c__DisplayClass1.<runSystrayMessage>b__0(Object sender, EventArgs args)
at MS.Internal.CoreInvokeHandler.InvokeEventHandler(Int32 typeIndex, Delegate handlerDelegate, Object sender, Object args)
at MS.Internal.JoltHelper.FireEvent(IntPtr unmanagedObj, IntPtr unmanagedObjArgs, Int32 argsTypeIndex, Int32 actualArgsTypeIndex, String eventName)}    System.Exception {System.NullReferenceException}

堆栈跟踪：

        StackTrace  "   at ContosoSocial.SetProgressIndicator.<>c__DisplayClass1.<runSystrayMessage>b__0(Object sender, EventArgs args)\r\n   at MS.Internal.CoreInvokeHandler.InvokeEventHandler(Int32 typeIndex, Delegate handlerDelegate, Object sender, Object args)\r\n   at MS.Internal.JoltHelper.FireEvent(IntPtr unmanagedObj, IntPtr unmanagedObjArgs, Int32 argsTypeIndex, Int32 actualArgsTypeIndex, String eventName)" string

我还是VS2013和Windows Phone编程的新手，所以在这里需要一些帮助来确定如何跟踪和解决这个问题？

错误似乎是随机的，这是显示系统托盘消息和调用方法的类的示例：

     class SetProgressIndicator
{

    public void runSystrayMessage(bool isVisible, string text, int length)
    {
        try
        {
            SystemTray.ProgressIndicator = new ProgressIndicator();
            SystemTray.ProgressIndicator.IsVisible = true;
            SystemTray.ProgressIndicator.Text = text;
            SystemTray.ProgressIndicator.IsIndeterminate = isVisible;
        }
        catch (System.InvalidOperationException e)
        {
            Debug.WriteLine("Exception caught in runSystrayMessage(): \r\n" + e);
        }


        DispatcherTimer timer = new DispatcherTimer();
        try
        {
            timer.Interval = TimeSpan.FromMilliseconds(length);
        }
        catch(ArgumentOutOfRangeException e)
        {
            Debug.WriteLine("Exception caught in runSystrayMessage(): \r\n" + e);
        }

        timer.Tick += (sender, args) =>
        {
            try
            {
                SystemTray.ProgressIndicator.IsVisible = false;
            }
            catch(System.InvalidOperationException e)
            {
                Debug.WriteLine("Exception caught in runSystrayMessage(): \r\n" + e);
            }
            timer.Stop();
        };

        timer.Start();
    }

}

}

调用方法示例：

    protected override void OnNavigatedTo(NavigationEventArgs e)
    {
        SetProgressIndicator progInd = new SetProgressIndicator();
        // Check for full licnece before removing ad's
        if (TrialExperienceHelper.LicenseMode == TrialExperienceHelper.LicenseModes.Full)
        {
            GOTPubCenter10.Visibility = Visibility.Collapsed;
        }

        // Dispaly message in system tray
        if (hasBeenVisited)
        {
            progInd.runSystrayMessage(true, "Entering house selection menu...", 2500);
        }
        else
        {
            progInd.runSystrayMessage(true, "Select house library to enter...", 8000);
            hasBeenVisited = true;
        }
    }

关于如何解决问题的想法和建议。

导航神秘时的Windows Phone NullReferenceException

0 个答案: