Home / Community & Support / Developer Productivity Tools Forums / Silverlight > MediaPlayer > RadMediaPlayer System.NullReferenceException : Object reference not set to an instance of an object

• Catherine

  Posted on May 30, 2011 (permalink)

  Hi,
  
  I got an error with the RadMediaPlay.
  
  Here is the Stacktrace :
     à Telerik.Windows.Controls.RadMediaPlayer.HandleCanExecuteJumpCommands(RadMediaPlayer player, ICommand command, Object parameter)
     à Telerik.Windows.Controls.RadMediaPlayer.MediaCommandCanExecute(Object sender, CanExecuteRoutedEventArgs e)
     à Telerik.Windows.Controls.CanExecuteRoutedEventArgs.InvokeEventHandler(Delegate genericHandler, Object target)
     à Telerik.Windows.RadRoutedEventArgs.InvokeHandler(Delegate handler, Object target)
     à Telerik.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RadRoutedEventArgs routedEventArgs)
     à Telerik.Windows.RouteItem.InvokeHandler(RadRoutedEventArgs routedEventArgs)
     à Telerik.Windows.EventRoute.InvokeHandlersImpl(Object source, RadRoutedEventArgs args, Boolean raisedAgain)
     à Telerik.Windows.EventRoute.InvokeHandlers(Object source, RadRoutedEventArgs args)
     à Telerik.Windows.RadRoutedEventHelper.RaiseEvent(DependencyObject element, RadRoutedEventArgs args)
     à Telerik.Windows.DependencyObjectExtensions.RaiseEvent(DependencyObject element, RadRoutedEventArgs e)
     à Telerik.Windows.Controls.RoutedCommand.CanExecute(Object parameter, UIElement target)
     à Telerik.Windows.Controls.RadButton.CanExecuteApply()
     à Telerik.Windows.Controls.RadButton.CanExecuteChanged(Object sender, EventArgs e)
     à Telerik.Windows.Controls.WeakEventHandlerManager.CallHandler(Object sender, EventHandler eventHandler)
     à Telerik.Windows.Controls.WeakEventHandlerManager.CallWeakReferenceHandlers(Object sender, List`1 handlers)
     à Telerik.Windows.Controls.CommandManager.RaiseRequerySuggested(Object obj)
     à Telerik.Windows.Controls.CommandManager.<RaiseRequerySuggested>b__5()
  
  My scenario is to open player in a window, the playlist is loaded dynamically.
  First, I created a usercontrol that uses the RadMediaPlayer. His name is PlayerControl.
  Here is a part of the UserControl :

  <telerik:RadMediaPlayer x:Name="player" 

                                  Loaded="PlayerLoaded" 

                                  Unloaded="PlayerUnloaded"

                                  MediaOpened="PlayerMediaOpened"

                                  MediaEnded="PlayerMediaEnded"

                                  Header="{Binding RelativeSource={RelativeSource Self}, Path=MediaElement}"

                                  ItemsSource="{Binding Items}"

                                  AutoPlay="{Binding AutoPlay}"

                                  IsAutoPlaylistAdvance="{Binding IsAutoPlaylistAdvance}"

                                  IsAutoReverse="{Binding IsAutoReverse}"

                                  IsPlaylistVisible="{Binding IsPlaylistVisible}"

                                  Height="{Binding VideoHeight}"

                                  Width="{Binding VideoWidth}"

                                  SelectedIndex="{Binding SelectedIndex, Mode=TwoWay}"

                                  SelectedItem="{Binding SelectedMediaItem, Mode=TwoWay}"

                                  IsVideoPanelHidden="{Binding IsVideoPanelHidden}"

                                  IsVideoPanelPinned="{Binding IsVideoPanelPinned }"

                                  HeaderTemplate="{Binding HeaderTemplate}">

                

              <telerik:RadMediaPlayer.ItemTemplateSelector>

                  <Template:MediaTemplateSelector>

                      <Template:MediaTemplateSelector.MediaItemTemplate>

                          <DataTemplate>

                              <telerik:ContainerBinding.ContainerBindings>

                                  <telerik:ContainerBindingCollection>

                                      <telerik:ContainerBinding PropertyName="Source" Binding="{Binding Source}" />

                                      <telerik:ContainerBinding PropertyName="IsSelected" Binding="{Binding IsSelected,Mode=TwoWay}" />

                                      <telerik:ContainerBinding PropertyName="Tag" Binding="{Binding}" />

                                  </telerik:ContainerBindingCollection>

                              </telerik:ContainerBinding.ContainerBindings>

                              <StackPanel HorizontalAlignment="Left" Orientation="Horizontal">

                                  <Image Source="{Binding Image}" Stretch="Uniform" Margin="4" />

                                  <TextBlock Text="{Binding Title}" VerticalAlignment="Center" Margin="4" />

                              </StackPanel>

                          </DataTemplate>

                      </Template:MediaTemplateSelector.MediaItemTemplate>

                      <Template:MediaTemplateSelector.VideoMediaItemTemplate>

                          <DataTemplate>

                              <telerik:ContainerBinding.ContainerBindings>

                                  <telerik:ContainerBindingCollection>

                                      <telerik:ContainerBinding PropertyName="Source" Binding="{Binding Source}" />

                                      <telerik:ContainerBinding PropertyName="IsSelected" Binding="{Binding IsSelected,Mode=TwoWay}" />

                                      <telerik:ContainerBinding PropertyName="Tag" Binding="{Binding}" />

                                      <telerik:ContainerBinding PropertyName="IsStreamingSource" Binding="{Binding IsStreamingSource}" />

                                      <telerik:ContainerBinding PropertyName="VideoWidth" Binding="{Binding VideoWidth}" />

                                      <telerik:ContainerBinding PropertyName="VideoHeight" Binding="{Binding VideoHeight}" />

                                      <telerik:ContainerBinding PropertyName="VideoStretch" Binding="{Binding VideoStretch}" />

                                  </telerik:ContainerBindingCollection>

                              </telerik:ContainerBinding.ContainerBindings>

                              <StackPanel HorizontalAlignment="Left" Orientation="Horizontal">

                                  <Image Source="{Binding Image}" Stretch="Uniform" Margin="4" />

                                  <TextBlock Text="{Binding Title}" VerticalAlignment="Center" Margin="4" />

                              </StackPanel>

                          </DataTemplate>

                      </Template:MediaTemplateSelector.VideoMediaItemTemplate>

                  </Template:MediaTemplateSelector>

              </telerik:RadMediaPlayer.ItemTemplateSelector>

     

          </telerik:RadMediaPlayer>

  
  A ViewModel is used to set the RadMediaPlayer's properties .
  
  The ViewModel contains some features to add and remove MediaItems from the RadMediaPlayer.
  

  public ObservableCollection<MediaItem> Items { get; internal set; }

    

   public void AddMediaItem( MediaItem item )

   {

         Items.Add(item);

   }

    

  public void RemoveMediaItem( MediaItem item )

          {

              if (Items.Contains(item))

              {

                    Items.Remove(item);

              }

          }

    

  public void Clear()

          {

              Items.Clear();

          }

  
  Finally, I try to open the window that contains the usercontrol.
  It works for 3 or 4 times (this is random) then I got the error
  

  // Template declared as a resource

  <DataTemplate x:Key="PlayerVideoTemplate">

          <Grid>

              <Player:PlayerControl x:Name="PlayerControl" HorizontalAlignment="Left" Controller="{Binding Controller}"/>

          </Grid>

      </DataTemplate>

    

  // The code

    

  // ViewModel for the PlayControl usercontrol

  Controller = new PlayerController

              {

                  SelectedIndex = 0,

                  AutoPlay = true,

                  IsAutoPlaylistAdvance = true,

                  ShowCommandsPanel = true,

                  MediaEnded = LectureMediaTerminee,

                  MediaOpened = LectureMedia

              };

    

  // add  a video to the playlist             

  _playList.AddLast(new VideoMediaItem

                          {

                              Source = videoSource,

                              Title = SelectedAppointment.ElpTitreDiff,

                              VideoStretch = Stretch.Fill

                          });

    

  // add the first value

   Controller.AddMediaItem(_playList.First.Value);

    

  // diplay the window

   var window = new RadWindow

                      {

                          DataContext = this,

                          Content = ((DataTemplate)Application.Current.Resources["PlayerVideoTemplate"]).LoadContent(),

                          MaxWidth = 1024,

                          MaxHeight = 768,

                          Header = "Player vidéo",

                          WindowStartupLocation = WindowStartupLocation.CenterScreen

                      };

   window.Show();

  
  Can you help me.
  
  Best ragards,
  C.Leoni.

  Reply

• Catherine

  Posted on May 31, 2011 (permalink)

  Hi again,
  
  I solved my problem.
  I created a single instance of the usercontrol and the window and this fixes the problem.
  Now it works.
  
  Best regards.
  C.Léoni.

  Reply

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