Null reference exception running system tray message WP8

Question

My WP8 app displays a message in the system tray for a few seconds when navigated to. But the following method I use to display the message always throws an System.NullReferenceException: Object reference not set to an instance of an object. I'm baffled to why this is, maybe someone can point out maybe whats wrong? The code is:

    private void runSystrayMessage(bool isVisible, string text, int length)
    {
        try
        {
            SystemTray.ProgressIndicator.IsVisible = true;
            SystemTray.ProgressIndicator.IsIndeterminate = isVisible;
            SystemTray.ProgressIndicator.Text = text;
        }
        catch (Exception e)
        {
            Debug.WriteLine("Exception caught" + e);
        }


        DispatcherTimer timer = new DispatcherTimer();
        try
        {
            timer.Interval = TimeSpan.FromMilliseconds(length);
        }
        catch(ArgumentOutOfRangeException e)
        {
            Debug.WriteLine("ArgumentOutOfrangeException caught" + e);
        }

        timer.Tick += (sender, args) =>
        {
            try
            {
                SystemTray.ProgressIndicator.IsVisible = false;
            }
            catch(System.InvalidOperationException e)
            {
                Debug.WriteLine("InvalidOperationException caught" + e);
            }
            timer.Stop();
        };
        timer.Start();
    }

The full Exception message is:

System.NullReferenceException: Object reference not set to an instance of an object.

at ContosoSocial.StartPage.<>c__DisplayClass1.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)

Why are you catching those exceptions? You're basically ignoring them. What if one of those exceptions means that something is wrong? — John Saunders, Sep 01 '14 at 02:54

score 4 · Accepted Answer · answered Sep 01 '14 at 03:40

4

Your problem is you have not created a new instance of the ProgressIndicator in your app. You have to instantiate one. Do it in the OnNavigatedTo method.

protected override void OnNavigatedTo(NavigationEventArgs e)
{
    base.OnNavigatedTo(e);
    SystemTray.ProgressIndicator = new ProgressIndicator();
}

That should fix your problem.

answered Sep 01 '14 at 03:40

Kasun Kodagoda

3,902
5
27
54

thanks I had tried it there earlier but working now!! – TripVoltage Sep 01 '14 at 04:03

Null reference exception running system tray message WP8

1 Answers1