protected override Size MeasureOverride(Size availableSize)
        {
            Panel panel = this.GroupLevelIndicatorPaneHost;

            if (panel == null)
            {
                return(base.MeasureOverride(availableSize));
            }

            DataGridContext dataGridContext = DataGridControl.GetDataGridContext(this);

            if (dataGridContext != null)
            {
                ObservableCollection <GroupDescription> groupDescriptions = DataGridContext.GetGroupDescriptionsHelper(dataGridContext.Items);

                int leafGroupLevel = GroupLevelIndicatorPane.GetGroupLevel(this);

                // If Indented is true (default), we use the total groupDescriptions.Count for this DataGridContext
                int correctedGroupLevel = (this.Indented == true) ? groupDescriptions.Count : leafGroupLevel;

                // Ensure that the GroupLevel retrieved does not exceeds the number of group descriptions for the DataGridContext
                correctedGroupLevel = Math.Min(correctedGroupLevel, groupDescriptions.Count);

                // Then finally, if the GroupLevel is -1, then indent at maximum.
                if (correctedGroupLevel == -1)
                {
                    correctedGroupLevel = groupDescriptions.Count;
                }

                if ((correctedGroupLevel > 0) &&
                    (this.AreGroupsFlattened))
                {
                    correctedGroupLevel = (this.Indented) ? 1 : 0;
                }

                UIElementCollection children = panel.Children;
                int childrenCount            = children.Count;

                // If we need to add/remove GroupLevelIndicators from the panel
                if (correctedGroupLevel != childrenCount)
                {
                    // When grouping change, we take for granted that the group deepness will change,
                    // so we initialize DataContext of the margin only in there.

                    // Clear all the panel's children!
                    children.Clear();

                    // Create 1 group margin content presenter for each group level
                    for (int i = correctedGroupLevel - 1; i >= 0; i--)
                    {
                        GroupLevelIndicator groupMargin = new GroupLevelIndicator();
                        groupMargin.DataContext = dataGridContext.GroupLevelDescriptions[i];
                        children.Insert(0, new GroupLevelIndicator());
                    }

                    childrenCount = correctedGroupLevel;
                    this.SetCurrentIndicatorCount(childrenCount);
                }

                object item = dataGridContext.GetItemFromContainer(this);

                for (int i = 0; i < childrenCount; i++)
                {
                    GroupLevelIndicator groupMargin = children[i] as GroupLevelIndicator;

                    CollectionViewGroup groupForIndicator = GroupLevelIndicatorPane.GetCollectionViewGroupHelper(
                        dataGridContext, groupDescriptions, item, i);

                    GroupConfiguration groupLevelConfig = GroupConfiguration.GetGroupConfiguration(
                        dataGridContext, groupDescriptions, dataGridContext.GroupConfigurationSelector, i, groupForIndicator);

                    if (groupLevelConfig != null)
                    {
                        Binding groupLevelIndicatorStyleBinding = BindingOperations.GetBinding(groupMargin, GroupLevelIndicator.StyleProperty);

                        if ((groupLevelIndicatorStyleBinding == null) || (groupLevelIndicatorStyleBinding.Source != groupLevelConfig))
                        {
                            groupLevelIndicatorStyleBinding        = new Binding("GroupLevelIndicatorStyle");
                            groupLevelIndicatorStyleBinding.Source = groupLevelConfig;
                            groupMargin.SetBinding(GroupLevelIndicator.StyleProperty, groupLevelIndicatorStyleBinding);
                        }
                    }
                    else
                    {
                        groupMargin.ClearValue(GroupLevelIndicator.StyleProperty);
                    }

                    // If the ShowIndicators property is False or there is already leafGroupLevel GroupLevelIndicators in the panel,
                    // the current newGroupMargin must be hidden.
                    if ((!GroupLevelIndicatorPane.GetShowIndicators(this)) || ((i >= leafGroupLevel) && (leafGroupLevel != -1)))
                    {
                        groupMargin.Visibility = Visibility.Hidden;
                    }
                    else
                    {
                        groupMargin.Visibility = Visibility.Visible;
                    }
                }
            }

            return(base.MeasureOverride(availableSize));
        }
    protected override Size MeasureOverride( Size availableSize )
    {
      Panel panel = this.GroupLevelIndicatorPaneHost;

      if( panel == null )
        return base.MeasureOverride( availableSize );

      DataGridContext dataGridContext = DataGridControl.GetDataGridContext( this );

      if( dataGridContext != null )
      {
        ObservableCollection<GroupDescription> groupDescriptions = DataGridContext.GetGroupDescriptionsHelper( dataGridContext.Items );

        int leafGroupLevel = GroupLevelIndicatorPane.GetGroupLevel( this );

        // If Indented is true (default), we use the total groupDescriptions.Count for this DataGridContext
        int correctedGroupLevel = ( this.Indented == true ) ? groupDescriptions.Count : leafGroupLevel;

        // Ensure that the GroupLevel retrieved does not exceeds the number of group descriptions for the DataGridContext
        correctedGroupLevel = Math.Min( correctedGroupLevel, groupDescriptions.Count );

        // Then finally, if the GroupLevel is -1, then indent at maximum.
        if( correctedGroupLevel == -1 )
          correctedGroupLevel = groupDescriptions.Count;

        if( ( correctedGroupLevel > 0 )
          && ( this.AreGroupsFlattened ) )
        {
          correctedGroupLevel = ( this.Indented ) ? 1 : 0;
        }

        UIElementCollection children = panel.Children;
        int childrenCount = children.Count;

        // If we need to add/remove GroupLevelIndicators from the panel
        if( correctedGroupLevel != childrenCount )
        {
          // When grouping change, we take for granted that the group deepness will change, 
          // so we initialize DataContext of the margin only in there.

          // Clear all the panel's children!
          children.Clear();

          // Create 1 group margin content presenter for each group level
          for( int i = correctedGroupLevel - 1; i >= 0; i-- )
          {
            GroupLevelIndicator groupMargin = new GroupLevelIndicator();
            groupMargin.DataContext = dataGridContext.GroupLevelDescriptions[ i ];
            children.Insert( 0, new GroupLevelIndicator() );
          }

          childrenCount = correctedGroupLevel;
          this.SetCurrentIndicatorCount( childrenCount );
        }

        object item = dataGridContext.GetItemFromContainer( this );

        for( int i = 0; i < childrenCount; i++ )
        {
          GroupLevelIndicator groupMargin = children[ i ] as GroupLevelIndicator;

          CollectionViewGroup groupForIndicator = GroupLevelIndicatorPane.GetCollectionViewGroupHelper( 
            dataGridContext, groupDescriptions, item, i );

          GroupConfiguration groupLevelConfig = GroupConfiguration.GetGroupConfiguration( 
            dataGridContext, groupDescriptions, dataGridContext.GroupConfigurationSelector, i, groupForIndicator );

          if( groupLevelConfig != null )
          {
            Binding groupLevelIndicatorStyleBinding = BindingOperations.GetBinding( groupMargin, GroupLevelIndicator.StyleProperty );

            if( ( groupLevelIndicatorStyleBinding == null ) || ( groupLevelIndicatorStyleBinding.Source != groupLevelConfig ) )
            {
              groupLevelIndicatorStyleBinding = new Binding( "GroupLevelIndicatorStyle" );
              groupLevelIndicatorStyleBinding.Source = groupLevelConfig;
              groupMargin.SetBinding( GroupLevelIndicator.StyleProperty, groupLevelIndicatorStyleBinding );
            }
          }
          else
          {
            groupMargin.ClearValue( GroupLevelIndicator.StyleProperty );
          }

          // If the ShowIndicators property is False or there is already leafGroupLevel GroupLevelIndicators in the panel,
          // the current newGroupMargin must be hidden.
          if( ( !GroupLevelIndicatorPane.GetShowIndicators( this ) ) || ( ( i >= leafGroupLevel ) && ( leafGroupLevel != -1 ) ) )
          {
            groupMargin.Visibility = Visibility.Hidden;
          }
          else
          {
            groupMargin.Visibility = Visibility.Visible;
          }
        }
      }

      return base.MeasureOverride( availableSize );
    }