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

[Catherine]

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.

[Catherine]

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.