using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Markup;
using System.ComponentModel;
using System.Windows.Controls;

namespace PropertiesAndMethods
{
  [DefaultProperty("MyContent"), ContentProperty("MyContent")]
  public class MyUIElement : Control
  {
    public static readonly DependencyProperty MyContentProperty;    
    /// <summary>
    /// Содержимое (строка), которое необходимо визуализировать
    /// </summary>
    [Bindable(true)]
    public string MyContent
    {
      get
      {
        return (string)base.GetValue(MyContentProperty);
      }
      set
      {
        base.SetValue(MyContentProperty, value);
      }
    }

    static MyUIElement()
    {
      FrameworkPropertyMetadata md = new FrameworkPropertyMetadata();
      md.AffectsArrange = true;
      md.AffectsMeasure = true;
      md.AffectsParentArrange = true;
      md.AffectsParentMeasure = true;
      md.CoerceValueCallback = CoerceValue;
      md.PropertyChangedCallback = PropChanged;
      md.AffectsRender = true;
      md.Inherits = true;
      md.DefaultValue = "sssss";
      MyContentProperty = DependencyProperty.Register("MyContent", typeof(string), typeof(MyUIElement), md, MyValidate);
    }

    private static object CoerceValue(DependencyObject d, object value)
    {
      if ((value == null) || ((string)value == string.Empty))
        return MyContentProperty.DefaultMetadata.DefaultValue;
      else
        return value;
    }

    private static bool MyValidate(object value)
    {
      return true;
    }


    private static void PropChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
      d.SetValue(MyContentProperty, "+++");
    }
  }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Media;
using System.Windows.Controls;

namespace PropertiesAndMethods
{
  public class Program
  {
    [STAThread]
    public static void Main()
    {
      Application app = new Application();
      Window win = new Window();

      MyUIElement me = new MyUIElement();
      me.MyContent = "wwwwww";
      me.Foreground = Brushes.Red;
      me.Background = Brushes.Green;
      me.FontSize = 12;
      me.HorizontalAlignment = HorizontalAlignment.Center;
      me.VerticalAlignment = VerticalAlignment.Center;
      me.Width = 80;
      me.Height = 40;

      //ContentControl me = new ContentControl();
      //me.Content = "wwwwww";
      //me.Foreground = Brushes.Red;
      //me.Background = Brushes.Green;
      //me.FontSize = 12;
      //me.HorizontalAlignment = HorizontalAlignment.Center;
      //me.VerticalAlignment = VerticalAlignment.Center;
      //me.Width = 80;
      //me.Height = 40;

      app.MainWindow = win;
      win.Content = me;
      win.Show();
      app.Run(win);
      //Console.Read();
    }
  }
}