Prism command binding not executing

Question

in my project i used wpf + prism.Inside a view,i must invoke a command inside a context menu, the command is defined into the viewmodel class.this is the view:

<UserControl x:Class="GrigoLync.Modules.LyncClient.Contatti.ContattiView"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
         xmlns:infr="clr-namespace:GrigoLync.infrastructure.Model.Lync;assembly=GrigoLync.infrastructure"
         xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"
         xmlns:diag="clr-namespace:System.Diagnostics;assembly=WindowsBase"
         mc:Ignorable="d"
         d:DesignHeight="300" d:DesignWidth="300" 

         >

<Grid>
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="*" />
    </Grid.ColumnDefinitions>
    <Grid.RowDefinitions>
        <RowDefinition />
    </Grid.RowDefinitions>
    <Label Grid.Column="0" Grid.Row="0" FontSize="12" Margin="5">Contatti</Label>

    <TreeView x:Name="groupTreeView" Margin="10" ItemsSource="{Binding GruppiLync}" >
        <TreeView.ItemTemplate>
            <HierarchicalDataTemplate ItemsSource="{Binding Path=ContattiLync}">
                <TextBlock Text="{Binding Path=Nome}" />
                <HierarchicalDataTemplate.ItemTemplate>
                    <DataTemplate>
                        <TextBlock Text="{Binding Path=Uri}" Tag="{Binding}">
                        <TextBlock.ContextMenu>
                            <ContextMenu> 
                                <MenuItem Header ="Invia messaggio istantaneo" 
                                          Command="{Binding PlacementTarget.Tag.SendInstantMessageCommand,RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=ContextMenu}, diag:PresentationTraceSources.TraceLevel=High}"/>                                         
                            </ContextMenu>
                        </TextBlock.ContextMenu>
                        </TextBlock>
                    </DataTemplate>
                </HierarchicalDataTemplate.ItemTemplate>
            </HierarchicalDataTemplate>
        </TreeView.ItemTemplate>
    </TreeView> 

</Grid>

the following is the viewmodel class:

 [Export(typeof(ContattiViewModel))]
[PartCreationPolicy(CreationPolicy.Shared)]
public class ContattiViewModel : NotificationObject
{

    private readonly ILyncClientService lyncClientService;
    private readonly IRegionManager regionManager;
    private readonly IEventAggregator eventAggregator;
    private List<GruppoLync> gruppiLync;
    private ICommand sendInstantMessageCommand;



     [ImportingConstructor]
    public ContattiViewModel(ILyncClientService lyncClientService, IRegionManager regionManager, IEventAggregator eventAggregator)
    {
        if (lyncClientService == null)
        {
            throw new ArgumentNullException("lyncClientService");
        }

        if (regionManager == null)
        {
            throw new ArgumentNullException("regionManager");
        }

        if (eventAggregator == null)
        {
            throw new ArgumentNullException("eventAggregator");
        }

        this.lyncClientService = lyncClientService;
        this.regionManager = regionManager;
        this.eventAggregator = eventAggregator;
        this.gruppiLync = lyncClientService.elencoGruppiLync();
        this.sendInstantMessageCommand = new DelegateCommand<object>(this.SendInstantMessage);

        //groupTreeView.DataItems = this.gruppiLync;

     }

     public ICommand SendInstantMessageCommand { get { return this.sendInstantMessageCommand; } }
     public List<GruppoLync> GruppiLync
     {
         get
         {
             return this.gruppiLync;
         }             
     }

     private void SendInstantMessage(object aContattoLync)
     {
         //This point is not executed!
     }



}

}

When i select from the user interface the menu item "Invia Messaggio istantaneo" the command is not invoke, This point is not executed can help me please?!!!!
this is the GruppoLync class:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.ComponentModel;
using System.Collections.ObjectModel;

namespace GrigoLync.infrastructure.Model.Lync
{
public class GruppoLync : INotifyPropertyChanged
{
    private string nome;
    public string Nome
    {
        get { return nome; }

        set { nome = value;
        OnPropertyChanged(new PropertyChangedEventArgs("Nome"));

        }
    }

    private ObservableCollection<ContattoLync> contattiLync;
    public ObservableCollection<ContattoLync> ContattiLync
    {
        get { return contattiLync; }
        set
        {
            contattiLync = value;
            OnPropertyChanged(new PropertyChangedEventArgs("ContattiLync"));
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;
    public void OnPropertyChanged(PropertyChangedEventArgs e)
    {
        if (PropertyChanged != null)
            PropertyChanged(this, e);
    }

    public GruppoLync(string nome, ObservableCollection<ContattoLync> contattiLync)
    {
        Nome = nome;
        ContattiLync = contattiLync;
    }
}

}

and this is ContattoLync class:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Input;
using Microsoft.Practices.Prism.Commands;

namespace GrigoLync.infrastructure.Model.Lync
{
public class ContattoLync
{

    public string Uri { get; set; }
    public string Stato { get; set; }

}
}

I report also the trace log of the binding:

System.Windows.Data Warning: 54 : Created BindingExpression (hash=37997052) for Binding (hash=17879784)
System.Windows.Data Warning: 56 :   Path: 'PlacementTarget.Tag.SendInstantMessageCommand'
System.Windows.Data Warning: 58 : BindingExpression (hash=37997052): Default mode resolved to OneWay
System.Windows.Data Warning: 59 : BindingExpression (hash=37997052): Default update trigger resolved to PropertyChanged
System.Windows.Data Warning: 60 : BindingExpression (hash=37997052): Attach to System.Windows.Controls.MenuItem.Command (hash=47163810)
System.Windows.Data Warning: 64 : BindingExpression (hash=37997052): RelativeSource (FindAncestor) requires tree context
System.Windows.Data Warning: 63 : BindingExpression (hash=37997052): Resolve source deferred
System.Windows.Data Warning: 54 : Created BindingExpression (hash=18607377) for Binding (hash=17879784)
System.Windows.Data Warning: 56 :   Path: 'PlacementTarget.Tag.SendInstantMessageCommand'
System.Windows.Data Warning: 58 : BindingExpression (hash=18607377): Default mode resolved to OneWay
System.Windows.Data Warning: 59 : BindingExpression (hash=18607377): Default update trigger resolved to PropertyChanged
System.Windows.Data Warning: 60 : BindingExpression (hash=18607377): Attach to System.Windows.Controls.MenuItem.Command (hash=32025604)
System.Windows.Data Warning: 64 : BindingExpression (hash=18607377): RelativeSource (FindAncestor) requires tree context
System.Windows.Data Warning: 63 : BindingExpression (hash=18607377): Resolve source deferred
System.Windows.Data Warning: 65 : BindingExpression (hash=37997052): Resolving source 
System.Windows.Data Warning: 68 : BindingExpression (hash=37997052): Found data context element: <null> (OK)
System.Windows.Data Warning: 71 :     Lookup ancestor of type ContextMenu:  queried ContextMenu (hash=46231978)
System.Windows.Data Warning: 70 :   RelativeSource.FindAncestor found ContextMenu (hash=46231978)
System.Windows.Data Warning: 76 : BindingExpression (hash=37997052): Activate with root item ContextMenu (hash=46231978)
System.Windows.Data Warning: 106 : BindingExpression (hash=37997052):   At level 0 - for ContextMenu.PlacementTarget found accessor DependencyProperty(PlacementTarget)
System.Windows.Data Warning: 102 : BindingExpression (hash=37997052): Replace item at level 0 with ContextMenu (hash=46231978), using accessor DependencyProperty(PlacementTarget)
System.Windows.Data Warning: 99 : BindingExpression (hash=37997052): GetValue at level 0 from ContextMenu (hash=46231978) using DependencyProperty(PlacementTarget): <null>
System.Windows.Data Warning: 104 : BindingExpression (hash=37997052):   Item at level 1 is null - no accessor
System.Windows.Data Warning: 101 : BindingExpression (hash=37997052): Replace item at level 2 with {NullDataItem}
System.Windows.Data Warning: 78 : BindingExpression (hash=37997052): TransferValue - got raw value {DependencyProperty.UnsetValue}
System.Windows.Data Warning: 86 : BindingExpression (hash=37997052): TransferValue - using fallback/default value <null>
System.Windows.Data Warning: 87 : BindingExpression (hash=37997052): TransferValue - using final value <null>
System.Windows.Data Warning: 65 : BindingExpression (hash=18607377): Resolving source 
System.Windows.Data Warning: 68 : BindingExpression (hash=18607377): Found data context element: <null> (OK)
System.Windows.Data Warning: 71 :     Lookup ancestor of type ContextMenu:  queried ContextMenu (hash=64235)
System.Windows.Data Warning: 70 :   RelativeSource.FindAncestor found ContextMenu (hash=64235)
System.Windows.Data Warning: 76 : BindingExpression (hash=18607377): Activate with root item ContextMenu (hash=64235)
System.Windows.Data Warning: 105 : BindingExpression (hash=18607377):   At level 0 using cached accessor for ContextMenu.PlacementTarget: DependencyProperty(PlacementTarget)
System.Windows.Data Warning: 102 : BindingExpression (hash=18607377): Replace item at level 0 with ContextMenu (hash=64235), using accessor DependencyProperty(PlacementTarget)
System.Windows.Data Warning: 99 : BindingExpression (hash=18607377): GetValue at level 0 from ContextMenu (hash=64235) using DependencyProperty(PlacementTarget): <null>
System.Windows.Data Warning: 104 : BindingExpression (hash=18607377):   Item at level 1 is null - no accessor
System.Windows.Data Warning: 101 : BindingExpression (hash=18607377): Replace item at level 2 with {NullDataItem}
System.Windows.Data Warning: 78 : BindingExpression (hash=18607377): TransferValue - got raw value {DependencyProperty.UnsetValue}
System.Windows.Data Warning: 86 : BindingExpression (hash=18607377): TransferValue - using fallback/default value <null>
System.Windows.Data Warning: 87 : BindingExpression (hash=18607377): TransferValue - using final value <null>

Answer 1

I solve the problem!!!!

 <TreeView x:Name="groupTreeView" Margin="10" ItemsSource="{Binding GruppiLync}">
        <TreeView.ItemTemplate>
            <HierarchicalDataTemplate ItemsSource="{Binding Path=ContattiLync}">
                <TextBlock Text="{Binding Path=Nome}" />
                <HierarchicalDataTemplate.ItemTemplate>
                    <DataTemplate>
                        <TextBlock Text="{Binding Path=Uri}" 
                                   Tag="{Binding DataContext, RelativeSource={RelativeSource AncestorType=TreeView}}">
                        <TextBlock.ContextMenu>
                            <ContextMenu DataContext="{Binding PlacementTarget.Tag, RelativeSource={RelativeSource Self}}"> 
                                <MenuItem Header ="Invia messaggio istantaneo" 
                                          Command="{Binding SendInstantMessageCommand, diag:PresentationTraceSources.TraceLevel=High}"
                                          CommandParameter="{Binding PlacementTarget.DataContext, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type ContextMenu}}}"/>
                            </ContextMenu>
                        </TextBlock.ContextMenu>
                        </TextBlock>
                    </DataTemplate>
                </HierarchicalDataTemplate.ItemTemplate>
            </HierarchicalDataTemplate>
        </TreeView.ItemTemplate>
    </TreeView> 

Thanks to All!!!

Answer 2

That's because ContextMenus are on a separate logical tree.
This means they don't "inherit" the DataContext of the element they act upon.

A workaround is this:

<TextBlock Tag="{Binding}"> <!-- You may have to use RelativeSource on this Binding, depending on which DataContext you're trying to reach -->
   <TextBlock.ContextMenu>
      <ContextMenu>
         <MenuItem Header="Name of the item" 
                  Command="{Binding PlacementTarget.Tag.MyCommand, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=ContextMenu}" />
      </ContextMenu>
   </TextBlock.ContextMenu>
</TextBlock>

This goes fetching MyCommand on the Tag of the PlacementTarget, in the ContextMenu of this MenuItem.

The PlacementTarget poiting to the TextBlock, and its Tag pointing to the DataContext of your view.

Answer 3

check the datacontext of the menuitem to see if its the correct one

Answer 4

I think to use binding with "RelativeSource={RelativeSource FindAncestor..." is a little strange, you'd rather bind directly to a property of the item set as the datacontext of your hierchical datatemplate.