Getting ID of button clicked inside itemSource?

Question

I have an observableCollection that I loop through using an itemSource inside my view. Each item in the observablecollection contains a button that sends a command (openSessionCommand) to the viewModel. My question is - how can I send and ID back to the viewModel of which button was clicked inside the itemSource?

<ItemsControl ItemsSource="{Binding AvailableSessions}" Margin="490,181,10.111,39.111">
<ItemsControl.ItemTemplate>
    <DataTemplate >
        <Border  BorderBrush="Black" Background="Gainsboro" BorderThickness="1" Margin="2">
            <Grid Background="#FFECECEC">
                <Grid.RowDefinitions>
                    <RowDefinition Height="Auto"/>
                    <RowDefinition Height="Auto"/>
                </Grid.RowDefinitions>

                <Button Command="{Binding RelativeSource={RelativeSource FindAncestor, 
                                    AncestorType={x:Type UserControl}}, Path=DataContext.OpenSessionCommand}" 
                        HorizontalAlignment="Left" Margin="10,10,0,0" 
                        VerticalAlignment="Top" Width="243" Height="42">
                    <TextBlock TextWrapping="Wrap">
                        <Run Text="{Binding SessionName}"/><LineBreak/>
                        <Run Text="{Binding Genre}"/><Run Text=" - "/><Run Text="{Binding Tempo}"/>
                    </TextBlock>
                </Button>

                <Label Content="{Binding AdminUsername}" HorizontalAlignment="Left" 
                    Margin="10,53,0,0" VerticalAlignment="Top" Width="243" Height="26"/>
                <Label Content="{Binding Client1Username}" HorizontalAlignment="Left" 
                    Margin="10,71,0,0" VerticalAlignment="Top" Width="243" Height="25"/>

            </Grid>
        </Border>
    </DataTemplate>
</ItemsControl.ItemTemplate>
<ItemsControl.Template>
    <ControlTemplate TargetType="ItemsControl">
        <ScrollViewer CanContentScroll="True">
            <ItemsPresenter/>
        </ScrollViewer>
    </ControlTemplate>
</ItemsControl.Template>

<ItemsControl.ItemsPanel>
    <ItemsPanelTemplate>
        <VirtualizingStackPanel/>
    </ItemsPanelTemplate>
</ItemsControl.ItemsPanel>

DelegateCommand:

public class DelegateCommand : ICommand
{
    private readonly Action _command;
    private readonly Func<bool> _canExecute;
    public event EventHandler CanExecuteChanged
    {
        add { CommandManager.RequerySuggested += value; }
        remove { CommandManager.RequerySuggested -= value; }
    }

    public DelegateCommand(Action command, Func<bool> canExecute = null)
    {
        if (command == null)
        throw new ArgumentNullException();
        _canExecute = canExecute;
        _command = command;
    }

    public void Execute(object parameter)
    {
        _command();
    }

    public bool CanExecute(object parameter)
    {
        return _canExecute == null || _canExecute();
    }
}

ICommand:

public ICommand OpenSessionCommand { get 
    { return new DelegateCommand(OpenSession); } 
}


public void OpenSession()
{
    ContinueReceiving = false;
    dispatcherTimer.Stop();

    Messenger.Default.Send<NavigateMessage>(
       new NavigateMessage(SessionViewModel.ViewName, this));
}

Answer 1

Use CommandParameter. Using {Binding} will pass the object in the observable collection that was clicked. More at MSDN

<Button Command="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type UserControl}}, Path=DataContext.OpenSessionCommand}" CommandParemeter="{Binding}" HorizontalAlignment="Left" Margin="10,10,0,0" VerticalAlignment="Top" Width="243" Height="42">
    <TextBlock TextWrapping="Wrap">
        <Run Text="{Binding SessionName}"/><LineBreak/>
        <Run Text="{Binding Genre}"/><Run Text=" - "/>
        <Run Text="{Binding Tempo}"/>
    </TextBlock>
</Button>

You will also need to adjust the OpenSessionCommand method signature to accept your parameter but that will depend on what Command implementation you are using.

UPDATE

Below is a generic implementation of DelegateCommand that accepts a parameter.

public class DelegateCommand<T> : ICommand where T : class
{
    private readonly Action<T> _command;
    private readonly Func<T, bool> _canExecute;
    public event EventHandler CanExecuteChanged
    {
        add { CommandManager.RequerySuggested += value; }
        remove { CommandManager.RequerySuggested -= value; }
    }

    public DelegateCommand(Action<T> command, Func<T, bool> canExecute = null)
    {
        if (command == null)
            throw new ArgumentNullException();
        _canExecute = canExecute;
        _command = command;
    }

    public void Execute(object parameter)
    {
        _command(parameter as T);
    }

    public bool CanExecute(object parameter)
    {
        return _canExecute == null || _canExecute(parameter as T);
    }
}

Now when you define your ICommand it should be something like this:

    public ICommand OpenSessionCommand { get { return new DelegateCommand<Button>(OpenSession); } }

    public void OpenSession(Button button)
    {
        ContinueReceiving = false;
        dispatcherTimer.Stop();

        Messenger.Default.Send<NavigateMessage>(new NavigateMessage(SessionViewModel.ViewName, this));
    }

Answer 2

I'm using something similar from within a listbox with a context menu.

<ContextMenu>
    <MenuItem Header ="Edit Exercise"   
              Command="{Binding EditExercise_Command}" 
      CommandParameter="{Binding SelectedExercise}"
/>

So, the method being called receives the exercise I was right clicking on as a parameter.

You can pass the button :)