<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.");
  }
}

//ILogger is the facade. Behind the scenes,
//a framework of your choice is used
ILogger logger = LoggerService.Logger;
logger.Log("hello world");

//create a new logger instance
string file = @"C:logfile.txt";
ILogger logger = BitFactoryLogger.CreateSingleFileLogger(file);

//use the global LoggerService to store the logger
LoggerService.SetLogger(logger);


...


//this will store the info in the log file
LoggerService.Logger.Log("This is an information");

public void LogData(ILogger logger)
{
  logger.Log("An information");
  logger.Log("Something Happened", TraceEventType.Warning);

  //LogItem is the most verbose version
  LogItem item = new LogItem();
  item.Message = "My Message";
  item.EventId = 999;
  item.Categories.Add("Foo");
  item.Priority = 10;
  logger.Log(item); 

  try
  {
    DivideByZero();
  }
  catch(Exception e)
  {
    logger.Log(e);
    logger.Log("Additional message.", e);
    logger.Log("Additional message.", e, TraceEventType.Critical);
  } 
}

//init IOC container builder
var builder = new ContainerBuilder();

//register single logger instance
ILogger logger;

#if (DEBUG)
  logger = new ConsoleLogger();
#else
  logger = BitFactoryLogger.CreateSingleFileLogger(AppUtil.LogFile);
#endif

//register logger
builder.Register(logger).As<ILogger>();

public void InitApp()
{
  //create a file logger (use BitFactory facade)
  string logFile = @"C:MyLogFile.txt";
  ILogger logger = BitFactoryLogger.CreateSingleFileLogger(logFile);

  //register as globally used logger
  LoggerService.SetLogger(logger);
}



private void Foo()
{
  try
  {
    DoSomethingWrong();
  }
  catch(Exception e)
  {
    //get registered logger and log exception
    ILogger logger = LoggerService.Logger;
    logger.Log(e);
  }
}

namespace Hardcodet.Util.Logging
{
  /// <summary>
  /// Provides a global repository for a given <see cref="ILogger"/>
  /// instance. This class ensures that the <see cref="Logger"/>
  /// property is never nullo - in case no logger is defined, it
  /// automatically installs a <see cref="NullLogger"/>
  /// instance.
  /// </summary>
  public static class LoggerService
  {
    private static ILogger logger = new NullLogger();


    /// <summary>
    /// Gets the installed <see cref="ILogger"/> implementation.
    /// </summary>
    /// <remarks>This property always returns a valid
    /// logger.</remarks>
    public static ILogger Logger
    {
      get { return logger; }
    }


    /// <summary>
    /// Installs a given logger or resets the <see cref="Logger"/>
    /// to a <see cref="NullLogger"/> instance if the
    /// <paramref name="loggerImplementation"/> is a null
    /// reference.
    /// </summary>
    /// <param name="loggerImplementation">The logger to be
    /// used globally, or a null reference in order to reset
    /// the service.</param>
    public static void SetLogger(ILogger loggerImplementation)
    {
      logger = loggerImplementation ?? new NullLogger();
    }
  }
}

using System;

namespace Hardcodet.Util.Logging
{
  /// <summary>
  /// A very simple implementation of <see cref="ILogger"/>
  /// that outputs all messages to the system console.
  /// </summary>
  public class ConsoleLogger : LoggerBase
  {
    /// <summary>
    /// Logs a given item to the console.
    /// </summary>
    /// <param name="item">The item to be logged.</param>
    /// <exception cref="ArgumentNullException">If <paramref name="item"/>
    /// is a null reference.</exception>
    public override void Log(LogItem item)
    {
      if (item == null) throw new ArgumentNullException("item");
      Console.Out.WriteLine(item.ToLogMessage());
    }

  }
}

using Microsoft.Practices.EnterpriseLibrary.Logging;


namespace Hardcodet.Util.Logging.EntLibFacade
{
  /// <summary>
  /// An implementation of the <see cref="ILogger"/>
  /// interface which outputs logged data using
  /// the <see cref="Logger"/> of the MS Enterprise
  /// Library.
  /// </summary>
  public class EnterpriseLibraryLogger : LoggerBase
  {

    /// <summary>
    /// Writes a log entry to the Enterprise Library's
    /// logging block. Output depends on the logging
    /// block's configuration.
    /// </summary>
    /// <param name="item">An log item which encapsulates
    /// information to be logged.</param>
    public override void Log(LogItem item)
    {
      LogEntry entry = ConvertLogItem(item);
      Logger.Write(entry);
    }
    
    
    
    /// <summary>
    /// Creates a <c>LogEntry</c> instance which can be processed
    /// by the Enterprise Library based on a given log item. 
    /// </summary>
    /// <param name="item">An log item which encapsulates information
    /// to be logged.</param>
    /// <returns>An Enterprise Library item which corresponds
    /// to the submitted <c>LogItem</c>.</returns>
    private static LogEntry ConvertLogItem(LogItem item)
    {
      //assign properties
      LogEntry entry = new LogEntry();
      entry.Message = item.Message;
      entry.Title = item.Title;
      entry.AddErrorMessage(item.ErrorMessage);
      entry.EventId = item.EventId;
      entry.Priority = item.Priority;
      entry.Severity = item.Severity;
      entry.TimeStamp = item.TimeStamp;

      foreach (string category in item.Categories)
      {
        item.Categories.Add(category);
      }
      
      return entry;
    }
 
  }
}

<Image
  Source="..SharedImagesHelpSmall.png"
  ToolTip="{ext:Info Title=ShareNameTitleToolTip, Body=ShareNameInfoToolTip}"
  />

<Image Source="..SharedImagesHelpSmall.png">
  <Image.ToolTip>
    <MyToolTipControl Header="My Title" Body="This is a ToolTip" />
  </Image.ToolTip>
</Image>

/// <summary>
/// A markup extension that returns a
/// <see cref="InfoPopup"/> control preconfigured
/// with header and text information according to the
/// <see cref="Title"/> and <see cref="Body"/>
/// properties.
/// </summary>
public class Info : MarkupExtension
{
  /// <summary>
  /// Either a title text or a resource key that can be used
  /// to look up the title.
  /// </summary>
  public string Title { get; set; }

  /// <summary>
  /// Either a tooltips' main text or a resource key that can be used
  /// to look up the text.
  /// </summary>
  public string Body { get; set; }

  /// <summary>
  /// Empty default constructor.
  /// </summary>
  public Info()
  {
  }

  /// <summary>
  /// Inits the <see cref="Info"/> markup extension
  /// with the title and body.
  /// </summary>
  public Info(string title, string body)
  {
    Title = title;
    Body = body;
  }

  /// <summary>
  /// Performs a lookup for the defined <see cref="Title"/> and
  /// <see cref="Info"/> and creates the tooltip control.
  /// </summary>
  /// <returns>
  /// A tooltip control.
  /// </returns>
  public override object ProvideValue(IServiceProvider serviceProvider)
  {
    //create the user control that 
    InfoPopup popup = new InfoPopup();

    if (!String.IsNullOrEmpty(Title))
    {
      //look up title - if the string is not a
      //resource key, use it directly
      var result = Resources.ResourceManager.GetObject(Title) ?? Title;
      popup.HeaderText = (string)result;
    }

    if (!String.IsNullOrEmpty(Body))
    {
      //look up body text - if the string is not a
      //resource key, use it directly
      var result = Resources.ResourceManager.GetObject(Body) ?? Body;
      popup.BodyText = (string)result;
    }

    //create tooltip and make sure only the content is visible
    ToolTip tt = new ToolTip();
    tt.HasDropShadow = false;
    tt.BorderThickness = new Thickness(0);
    tt.Background = Brushes.Transparent;
    tt.Content = popup;

    return tt;
  }
}

<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"
/>