Specify Command for MenuItem in a DataTemplate

I think you need to wrap your TextBlock in a MenuItem:

<DataTemplate x:Key="itemTemplate">
    <MenuItem Command={Binding ...}>
        <TextBlock Text={Binding ...} />
    </MenuItem>
</DataTemplate>

But I don't have an IDE in front of me right now to try this. Let me know how it goes.

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Looks like you need to use the ItemContainerStyle as seen here. Sorry for leading you down the wrong path at the start there - but I got in front of an IDE and this works:

<ContextMenu.ItemContainerStyle>
    <Style TargetType="MenuItem">
        <Setter Property="Command" Value="{Binding ...}"/>
    </Style>
</ContextMenu.ItemContainerStyle>

Although this is only a slight variation on Martin Harris's answer, I thought I'd share it anyway. I found it more useful specify a single command for the whole collection and also send along a CommandParameter:

<MenuItem.ItemContainerStyle>
    <Style TargetType="MenuItem">
       <Setter Property="Command" Value="{x:Static v:ViewModel.CommandForAll}"/>
       <Setter Property="CommandParameter" Value="{Binding ValueForCommand}"/>
    </Style>
</MenuItem.ItemContainerStyle>

Then you can determine what to do in the handler for the command:

private void CommandForAll_Executed(object sender, ExecutedRoutedEventArgs e)
{
    var cmdParam = e.Paramater as ExpectedType
    if (cmdParam != null)
        //DoStuff...
}