How to: Implement Custom Grouping

• Nov 13, 2018
• 3 minutes to read

Assume that a Grid View’s “Order Sum” column contains numbers. When grouping is applied to this column, the rows which have values between 0 and 99 in this column should be combined into a single group, the rows whose values fall between 100 and 199 should be combined into another group, etc. To provide custom grouping logic the column’s GridColumn.SortMode property should be set to ColumnSortMode.Custom and the GridView.CustomColumnGroup event should be handled to implement the algorithm. In the following example the event’s Result parameter is set to 0 if the two rows being compared should be placed within the same group.

The ColumnView.CustomColumnDisplayText event is handled to replace the default text displayed within group rows.

The result of data being custom grouped is shown below:

C#

using DevExpress.XtraGrid;
using DevExpress.XtraGrid.Views.Base;
using DevExpress.XtraGrid.Views.Grid;
using DevExpress.XtraGrid.Views.Grid.ViewInfo;

// ...
gridView1.Columns["Order Sum"].SortMode = ColumnSortMode.Custom;

private void gridView1_CustomColumnGroup(object sender, CustomColumnSortEventArgs e) {
   if(e.Column.FieldName == "Order Sum") {
      double x = Math.Floor(Convert.ToDouble(e.Value1) / 100);
      double y = Math.Floor(Convert.ToDouble(e.Value2) / 100);
      int res = Comparer.Default.Compare(x, y);
      if(x > 14 && y > 14) res = 0;
      e.Result = res;
      e.Handled = true;
   }
}

private void gridView_CustomColumnDisplayText(object sender, DevExpress.XtraGrid.Views.Base.CustomColumnDisplayTextEventArgs e) {
    GridView view = sender as GridView;
    if(view == null) return;
    if (e.Column.FieldName == "Order Sum" && e.IsForGroupRow) {
        double rowValue = Convert.ToDouble(view.GetGroupRowValue(e.GroupRowHandle, e.Column));
        double val = Math.Floor(rowValue / 100);
        string groupRowInterval = string.Format("{0:c} - {1:c} ", val * 100, (val + 1) * 100);
        if (val > 14)
            groupRowInterval = string.Format(">= {0:c} ", val * 100);
        e.DisplayText = "Order Sum: " + groupRowInterval;
    }
}

VB.NET

Imports DevExpress.XtraGrid
Imports DevExpress.XtraGrid.Views.Base
Imports DevExpress.XtraGrid.Views.Grid
Imports DevExpress.XtraGrid.Views.Grid.ViewInfo

   ' ...
   GridView1.Columns("Order Sum").SortMode = ColumnSortMode.Custom

Private Sub GridView1_CustomColumnGroup(ByVal sender As Object, _
ByVal e As CustomColumnSortEventArgs) Handles GridView1.CustomColumnGroup
   If e.Column.FieldName = "Order Sum" Then
      Dim x As Double = Math.Floor(Convert.ToDouble(e.Value1) / 100)
      Dim y As Double = Math.Floor(Convert.ToDouble(e.Value2) / 100)
      Dim res As Integer = Comparer.Default.Compare(x, y)
      If x > 14 And y > 14 Then res = 0
      e.Result = res
      e.Handled = True
   End If
End Sub

Private Sub GridView1_CustomColumnDisplayText(ByVal sender As Object, _
ByVal e As DevExpress.XtraGrid.Views.Base.CustomColumnDisplayTextEventArgs) Handles GridView1.CustomColumnDisplayText
    Dim view As GridView = sender
    If view Is Nothing Then
        Return
    End If
    If e.Column.FieldName = "Order Sum" AndAlso e.IsForGroupRow Then
        Dim rowValue As Double = Convert.ToDouble(view.GetGroupRowValue(e.GroupRowHandle, e.Column))
        Dim val As Double = Math.Floor(rowValue / 100)
        Dim groupRowInterval As String = String.Format("{0:c} - {1:c} ", val * 100, (val + 1) * 100)
        If val > 14 Then
            groupRowInterval = String.Format(">= {0:c} ", val * 100)
        End If
        e.DisplayText = Convert.ToString("Order Sum: ") & groupRowInterval
    End If
End Sub