<Window.Resources>

  <cmd:HelloWorldCommand x:Key="SayHello" />

</Window.Resources>

<Button Command="{StaticResource SayHello}" />

<Button Command="{cmd:HelloWorldCommand}" />

/// <summary>
/// Basic implementation of the <see cref="ICommand"/>
/// interface, which is also accessible as a markup
/// extension.
/// </summary>
public abstract class CommandExtension<T> : MarkupExtension, ICommand
    where T:class, ICommand, new()
{
  /// <summary>
  /// A singleton instance.
  /// </summary>
  private static T command;


  /// <summary>
  /// Gets a shared command instance.
  /// </summary>
  public override object ProvideValue(IServiceProvider serviceProvider)
  {
    if (command == null) command = new T();
    return command;
  }


  /// <summary>
  /// Fires when changes occur that affect whether
  /// or not the command should execute.
  /// </summary>
  public event EventHandler CanExecuteChanged
  {
    add { CommandManager.RequerySuggested += value; }
    remove { CommandManager.RequerySuggested -= value; }
  }
  

  /// <summary>
  /// Defines the method to be called when the command is invoked.
  /// </summary>
  /// <param name="parameter">Data used by the command.
  /// If the command does not require data to be passed,
  /// this object can be set to null.
  /// </param>
  public abstract void Execute(object parameter);


  /// <summary>
  /// Defines the method that determines whether the command
  /// can execute in its current state.
  /// </summary>
  /// <returns>
  /// This default implementation always returns true.
  /// </returns>
  /// <param name="parameter">Data used by the command.  
  /// If the command does not require data to be passed,
  /// this object can be set to null.
  /// </param>
  public virtual bool CanExecute(object parameter)
  {
    return true;
  }
}

public class HelloWorldCommand : CommandExtension<HelloWorldCommand>
{
  public override void Execute(object parameter)
  {
    MessageBox.Show("Hello world.");
  }
}

<Window ...>
  <Grid>
    <Grid.Resources>
      <r:RibbonCommand
        x:Key="MyCommand"
        Executed="OnRibbonClicked"
        LabelTitle="Click Me" />
    </Grid.Resources>

    <!-- a ribbon that only displays a command in the quick access toolbar -->
    <r:Ribbon>
      <r:Ribbon.QuickAccessToolBar>
        <r:RibbonQuickAccessToolBar>
          <r:RibbonButton
            Command="{StaticResource MyCommand}"
            r:RibbonQuickAccessToolBar.Placement="InToolBar" />
        </r:RibbonQuickAccessToolBar>
      </r:Ribbon.QuickAccessToolBar>
    </r:Ribbon>
  </Grid>
</Window>

private void OnRibbonClicked(object sender, ExecutedRoutedEventArgs e)
{
  MessageBox.Show("Ribbon command executing.");
}

///<summary>
/// Base class for custom <see cref="RibbonCommand"/>
/// implementations.
///</summary>
public abstract class RibbonCommandBase : RibbonCommand
{
  /// <summary>
  /// Creates the command and registers weak event listeners.
  /// </summary>
  protected RibbonCommandBase()
  {
    Executed += OnExecute;
    CanExecute += OnCanExecute;
  }


  /// <summary>
  /// Determines whether the command can be executed or not.
  /// The default implementation always allows that.
  /// </summary>
  protected virtual void OnCanExecute(object sender, CanExecuteRoutedEventArgs e)
  {
    e.CanExecute = true;
  }


  /// <summary>
  /// Command implementation - executes command logic.
  /// </summary>
  protected abstract void OnExecute(object sender, ExecutedRoutedEventArgs e);
}

public class MessageCommand : RibbonCommandBase
{
  protected override void OnExecute(object sender, ExecutedRoutedEventArgs e)
  {
    MessageBox.Show("Ribbon command executing.");
  }
}

<!-- Custom command - can be declared in a resource dictionary -->
<cmd:MessageCommand x:Key="MyCommand"
                    LabelTitle="Click Me"
                    SmallImageSource="About.png"
/>

<!-- the popup that is displayed if user moves rows -->
<Popup
  x:Name="popup1"
  IsHitTestVisible="False"
  Placement="RelativePoint"
  PlacementTarget="{Binding ElementName=me}"
  AllowsTransparency="True">
  <Border
    BorderBrush="{DynamicResource CellBorderBrush}"
    BorderThickness="2"
    Background="White"
    Opacity="0.75">
    <StackPanel
      Orientation="Horizontal"
      Margin="4,3,8,3">
      <Image
        Source="/Shared/Images/DragInsert.png"
        Width="16"
        Height="16" />
      <TextBlock
        Style="{DynamicResource DefaultLabel}"
        FontWeight="Bold"
        VerticalAlignment="Center"
        Text="{Binding ElementName=me, Path=DraggedItem.Name}"
        Margin="8,0,0,0" />
    </StackPanel>
  </Border>
</Popup>

<dg:DataGrid
  BeginningEdit="OnBeginEdit"
  CellEditEnding="OnEndEdit"
  .. />

/// <summary>
/// State flag which indicates whether the grid is in edit
/// mode or not.
/// </summary>
public bool IsEditing { get; set; }

private void OnBeginEdit(object sender, DataGridBeginningEditEventArgs e)
{
  IsEditing = true;
  //in case we are in the middle of a drag/drop operation, cancel it...
  if (IsDragging) ResetDragDrop();
}

private void OnEndEdit(object sender, DataGridCellEditEndingEventArgs e)
{
  IsEditing = false;
}

private void OnMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
  //exit if in edit mode
  if (IsEditing) return;

  //find the clicked row
  var row = UIHelpers.TryFindFromPoint<DataGridRow>((UIElement) sender,
                                                    e.GetPosition(shareGrid));
  if (row == null) return;

  //set flag that indicates we're capturing mouse movements
  IsDragging = true;
  DraggedItem = (IShareConfiguration) row.Item;
}

/// <summary>
/// Completes a drag/drop operation.
/// </summary>
private void OnMouseLeftButtonUp(object sender, MouseButtonEventArgs e)
{
  if (!IsDragging || IsEditing)
  {
    return;
  }

  //get the target item
  ShareConfiguration targetItem = (ShareConfiguration) shareGrid.SelectedItem;

  if (targetItem == null || !ReferenceEquals(DraggedItem, targetItem))
  {
    //remove the source from the list
    ShareList.Remove(DraggedItem);

    //get target index
    var targetIndex = ShareList.IndexOf(targetItem);

    //move source at the target's location
    ShareList.Insert(targetIndex, DraggedItem);

    //select the dropped item
    shareGrid.SelectedItem = DraggedItem;
  }

  //reset
  ResetDragDrop();
}

/// <summary>
/// Completes a drag/drop operation.
/// </summary>
private void OnMouseLeftButtonUp(object sender, MouseButtonEventArgs e)
{
  if (!IsDragging || IsEditing || shareGrid.SelectedItem == null)
  {
    return;
  }
  
  //get the target item
  IShareConfiguration targetItem = (IShareConfiguration)shareGrid.SelectedItem;

  if (!ReferenceEquals(DraggedItem, targetItem))
  {
    //the actual business logic that works on source and target
  }

  //reset
  ResetDragDrop();
}

/// <summary>
/// Closes the popup and resets the
/// grid to read-enabled mode.
/// </summary>
private void ResetDragDrop()
{
  IsDragging = false;
  popup1.IsOpen = false;
  shareGrid.IsReadOnly = false;      
}

<TextBox
    x:Name="name"
    Text="world" />

<TextBlock
    Text="{Binding ElementName=name,
                   Path=Text,
                   StringFormat=hello {0}}" />

//use resource file to create message
var msg = Resources.Ask_Whether_To_Connect_To_New_Share;
msg = String.Format(msg, configuration.Name);

//display dialog
MessageBoxResult doConnect = Dialogs.ShowYesNo(msg);

<!-- Display a formatted text -->
<TextBlock
  x:Name="Title"
  Text="{Binding Path=Name,
                 StringFormat={ext:Resource Ask_Whether_To_Connect_To_New_Share}}"
 />

/// <summary>
/// A markup extension that provides simple access to a given
/// entry in the application's <see cref="Resources"/> file.
/// </summary>
public class Resource : MarkupExtension
{
  /// <summary>
  /// The resource key to be used for the lookup.
  /// </summary>
  public string ResourceKey { get; set; }


  /// <summary>
  /// Inits the <see cref="Resource"/> markup extension
  /// with the key to be assigned.
  /// </summary>
  /// <param name="resourceKey">The resource key to be assigned.</param>
  public Resource(string resourceKey)
  {
    ResourceKey = resourceKey;
  }


  /// <summary>
  /// Performs a lookup for the defined <see cref="ResourceKey"/>.
  /// </summary>
  /// <returns>
  /// The value of the resource that is specified by the
  /// <see cref="ResourceKey"/> property. If the property is not
  /// set, a null reference is returned.
  /// </returns>
  public override object ProvideValue(IServiceProvider serviceProvider)
  {
    if (String.IsNullOrEmpty(ResourceKey)) return null;
    return Resources.ResourceManager.GetObject(ResourceKey);
  }
}