System.NullReferenceException Windows Phone 8 - windows-phone-8

Question

I am experiencing a strange issue, since normally this works like a charm on Windows Phone 7. I just upgraded the project to Windows Phone 8 for getting the XAP file, it crashes.
This is the part of the code which "fails":
/// Holds the push channel that is created or found.
HttpNotificationChannel pushChannel;
// The name of our push channel.
string channelName = "ToastSampleChannel";
InitializeComponent();
// Try to find the push channel.
pushChannel = HttpNotificationChannel.Find(channelName);
// If the channel was not found, then create a new connection to the push service.
if (pushChannel == null)
{
pushChannel = new HttpNotificationChannel(channelName);
// Register for all the events before attempting to open the channel.
pushChannel.ChannelUriUpdated += new EventHandler<NotificationChannelUriEventArgs>(PushChannel_ChannelUriUpdated);
pushChannel.ErrorOccurred += new EventHandler<NotificationChannelErrorEventArgs>(PushChannel_ErrorOccurred);
// Register for this notification only if you need to receive the notifications while your application is running.
//pushChannel.ShellToastNotificationReceived += new EventHandler<NotificationEventArgs>(PushChannel_ShellToastNotificationReceived);
pushChannel.Open();
// Bind this new channel for toast events.
pushChannel.BindToShellToast();
}
else
{
// The channel was already open, so just register for all the events.
pushChannel.ChannelUriUpdated += new EventHandler<NotificationChannelUriEventArgs>(PushChannel_ChannelUriUpdated);
pushChannel.ErrorOccurred += new EventHandler<NotificationChannelErrorEventArgs>(PushChannel_ErrorOccurred);
// Register for this notification only if you need to receive the notifications while your application is running.
//pushChannel.ShellToastNotificationReceived += new EventHandler<NotificationEventArgs>(PushChannel_ShellToastNotificationReceived);
// Display the URI for testing purposes. Normally, the URI would be passed back to your web service at this point.
System.Diagnostics.Debug.WriteLine(pushChannel.ChannelUri.ToString());
// MessageBox.Show(String.Format("Channel Uri is {0}", pushChannel.ChannelUri.ToString()));
}
string token = pushChannel.ChannelUri.ToString();
//System.Diagnostics.Debug.WriteLine("token");
//System.Diagnostics.Debug.WriteLine(token);
//int active = 1;
object uniqueID;
string deviceID;
if (Microsoft.Phone.Info.DeviceExtendedProperties.TryGetValue("DeviceUniqueId", out uniqueID) == true)
{
WB1.Navigated += WB1_Navigated;
//getting udid
byte[] bID = (byte[])uniqueID;
deviceID = Convert.ToBase64String(bID); // There you go
}
When it crash, the next line in being execute would be WB1.Navigated += WB1_Navigated;
So I think the error is in the previous if-condition, but I am not able to see what is wrong because before upgrading the target in project properties, it worked fine.
Any idea?
I add WB1_Navigated and other related methods:
void WB1_Navigated(object sender, System.Windows.Navigation.NavigationEventArgs e)
{
visitedUrls.Push(e.Uri);
}
private void WebBrowser_OnLoadCompleted(object sender, System.Windows.Navigation.NavigationEventArgs e)
{
this.CoverImage.Visibility = Visibility.Collapsed;
}
protected override void OnBackKeyPress(System.ComponentModel.CancelEventArgs e)
{
if (visitedUrls.Count > 1)
{
visitedUrls.Pop();
WB1.Navigate(visitedUrls.Pop());
e.Cancel = true;
}
}
As petition, I show my xml code:
<phone:PhoneApplicationPage
x:Class="WindowsPush.MainPage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:phone="clr-namespace:Microsoft.Phone.Controls;assembly=Microsoft.Phone"
xmlns:shell="clr-namespace:Microsoft.Phone.Shell;assembly=Microsoft.Phone"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d" FontFamily="{StaticResource PhoneFontFamilyNormal}"
FontSize="{StaticResource PhoneFontSizeNormal}"
Foreground="{StaticResource PhoneForegroundBrush}"
SupportedOrientations="Portrait" Orientation="Portrait"
shell:SystemTray.IsVisible="True" d:DesignHeight="768" d:DesignWidth="480">
<!--LayoutRoot is the root grid where all page content is placed-->
<!--Sample code showing usage of ApplicationBar-->
<!--<phone:PhoneApplicationPage.ApplicationBar>
<shell:ApplicationBar IsVisible="True" IsMenuEnabled="True">
<shell:ApplicationBarIconButton IconUri="/Images/appbar_button1.png" Text="Button 1"/>
<shell:ApplicationBarIconButton IconUri="/Images/appbar_button2.png" Text="Button 2"/>
<shell:ApplicationBar.MenuItems>
<shell:ApplicationBarMenuItem Text="MenuItem 1"/>
<shell:ApplicationBarMenuItem Text="MenuItem 2"/>
</shell:ApplicationBar.MenuItems>
</shell:ApplicationBar>
</phone:PhoneApplicationPage.ApplicationBar>-->
<Grid x:Name="LayoutRoot" Background="Transparent">
<Grid.RowDefinitions>
<RowDefinition Height="*"/>
</Grid.RowDefinitions>
<phone:WebBrowser Name="WB1" LoadCompleted="WebBrowser_OnLoadCompleted"/>
<Image x:Name="CoverImage" Width="Auto" Height="Auto" Source="\SplashScreenImage.jpg"></Image>
</Grid>
</phone:PhoneApplicationPage>

Answer 1

You are getting (probably) your Exception in line:
string token = pushChannel.ChannelUri.ToString();
You get your ChanelUri after some time, and before you get it it's null. Move your token to PushChannel_ChannelUriUpdated:
private void PushChannel_ChannelUriUpdated(object sender, NotificationChannelUriEventArgs e)
{
string token = pushChannel.ChannelUri.ToString();
}
EDIT - source information
According to this blog:
The Open channel (a few lines of code later) is an asynchronous operation (therefore the need to attach an event handler that gets triggered once the open operation completes). If it is successful, the ChannelUriUpdate event is raised, if it fails, most probably HttpNotificationChannel will raise an ExceptionOccurred event.