<Grid>
  <Grid.RowDefinitions>
    <RowDefinition Height="Auto"/>
    <RowDefinition/>
    <RowDefinition/>
    <RowDefinition/>
    <RowDefinition/>
    <RowDefinition/>
    <RowDefinition Height="2*"/>
  </Grid.RowDefinitions>
  <Grid.ColumnDefinitions>
    <ColumnDefinition Width="100"/>
    <ColumnDefinition/>
  </Grid.ColumnDefinitions>
 
  <TextBlock Text="User Details" FontSize="20"
          HorizontalAlignment="Center"
          Grid.ColumnSpan="2"/>
 
  <TextBlock Text="Forename:"
              Grid.Row="1"/>
  <TextBox Text="Jeremy"
            Grid.Column="1" Grid.Row="1"/>
 
  <TextBlock Text="Surname:"
              Grid.Row="2"/>
  <TextBox Text="James"
            Grid.Column="1" Grid.Row="2"/>
 
  <TextBlock Text="Age:"
              Grid.Row="3"/>
  <TextBox Text="24"
            Grid.Column="1" Grid.Row="3"/>
 
  <TextBlock Text="Phone:"
              Grid.Row="4"/>
  <TextBox Text="+44 191 555467"
            Grid.Column="1" Grid.Row="4"/>
 
  <TextBlock Text="Notes:"
              Grid.Row="5"/>
  <TextBox Text="A multi-line block of text ..." 
            TextWrapping="Wrap"
            Grid.Row="6" Grid.ColumnSpan="2"/>
</Grid>

<Grid local:GridUtils.ColumnDefinitions="100,"
      local:GridUtils.RowDefinitions="Auto,,,,,,2*">
 
  <TextBlock Text="User Details" FontSize="20"
          HorizontalAlignment="Center"
          Grid.ColumnSpan="2"/>
 
  <TextBlock Text="Forename:"
              Grid.Row="1"/>
  <TextBox Text="Jeremy"
            Grid.Column="1" Grid.Row="1"/>
 
  <TextBlock Text="Surname:"
              Grid.Row="2"/>
  <TextBox Text="James"
            Grid.Column="1" Grid.Row="2"/>
 
  <TextBlock Text="Age:"
              Grid.Row="3"/>
  <TextBox Text="24"
            Grid.Column="1" Grid.Row="3"/>
 
  <TextBlock Text="Phone:"
              Grid.Row="4"/>
  <TextBox Text="+44 191 555467"
            Grid.Column="1" Grid.Row="4"/>
 
  <TextBlock Text="Notes:"
              Grid.Row="5"/>
  <TextBox Text="A multi-line block of text ..." 
            TextWrapping="Wrap"
            Grid.Row="6" Grid.ColumnSpan="2"/>
</Grid>

using System.Windows;
using System.Windows.Controls;
 
namespace SimplifiedGrid
{
  public class GridUtils
  {
    #region RowDefinitions attached property
 
    /// <summary>
    /// Identified the RowDefinitions attached property
    /// </summary>
    public static readonly DependencyProperty RowDefinitionsProperty =
        DependencyProperty.RegisterAttached("RowDefinitions", typeof(string), typeof(GridUtils),
            new PropertyMetadata("", new PropertyChangedCallback(OnRowDefinitionsPropertyChanged)));
 
    /// <summary>
    /// Gets the value of the RowDefinitions property
    /// </summary>
    public static string GetRowDefinitions(DependencyObject d)
    {
      return (string)d.GetValue(RowDefinitionsProperty);
    }
 
    /// <summary>
    /// Sets the value of the RowDefinitions property
    /// </summary>
    public static void SetRowDefinitions(DependencyObject d, string value)
    {
      d.SetValue(RowDefinitionsProperty, value);
    }
 
    /// <summary>
    /// Handles property changed event for the RowDefinitions property, constructing
    /// the required RowDefinitions elements on the grid which this property is attached to.
    /// </summary>
    private static void OnRowDefinitionsPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
      Grid targetGrid = d as Grid;
 
      // construct the required row definitions
      targetGrid.RowDefinitions.Clear();
      string rowDefs = e.NewValue as string;
      var rowDefArray = rowDefs.Split(',');
      foreach (string rowDefinition in rowDefArray)
      {
        if (rowDefinition.Trim() == "")
        {
          targetGrid.RowDefinitions.Add(new RowDefinition());
        }
        else
        {
          targetGrid.RowDefinitions.Add(new RowDefinition()
          {
            Height = ParseLength(rowDefinition)
          });
        }
      }
    }
 
    #endregion
 
 
    #region ColumnDefinitions attached property
 
    /// <summary>
    /// Identifies the ColumnDefinitions attached property
    /// </summary>
    public static readonly DependencyProperty ColumnDefinitionsProperty =
        DependencyProperty.RegisterAttached("ColumnDefinitions", typeof(string), typeof(GridUtils),
            new PropertyMetadata("", new PropertyChangedCallback(OnColumnDefinitionsPropertyChanged)));
 
    /// <summary>
    /// Gets the value of the ColumnDefinitions property
    /// </summary>
    public static string GetColumnDefinitions(DependencyObject d)
    {
      return (string)d.GetValue(ColumnDefinitionsProperty);
    }
 
    /// <summary>
    /// Sets the value of the ColumnDefinitions property
    /// </summary>
    public static void SetColumnDefinitions(DependencyObject d, string value)
    {
      d.SetValue(ColumnDefinitionsProperty, value);
    }
 
    /// <summary>
    /// Handles property changed event for the ColumnDefinitions property, constructing
    /// the required ColumnDefinitions elements on the grid which this property is attached to.
    /// </summary>
    private static void OnColumnDefinitionsPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
      Grid targetGrid = d as Grid;
 
      // construct the required column definitions
      targetGrid.ColumnDefinitions.Clear();
      string columnDefs = e.NewValue as string;
      var columnDefArray = columnDefs.Split(',');
      foreach (string columnDefinition in columnDefArray)
      {
        if (columnDefinition.Trim() == "")
        {
          targetGrid.ColumnDefinitions.Add(new ColumnDefinition());
        }
        else
        {
          targetGrid.ColumnDefinitions.Add(new ColumnDefinition()
          {
            Width = ParseLength(columnDefinition)
          });
        }
      }
    }
 
    #endregion
 
    /// <summary>
    /// Parses a string to create a GridLength
    /// </summary>
    private static GridLength ParseLength(string length)
    {
      length = length.Trim();
 
      if (length.ToLowerInvariant().Equals("auto"))
      {
        return new GridLength(0, GridUnitType.Auto);
      }
      else if (length.Contains("*"))
      {
        length = length.Replace("*","");
        if (string.IsNullOrEmpty(length)) length = "1";
        return new GridLength(double.Parse(length), GridUnitType.Star);
      }
 
      return new GridLength(double.Parse(length), GridUnitType.Pixel);
    }
  }
}