RadControls for WinForms
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Custom grouping is a flexible mechanism for creating RadGridView groups by using custom logic. It has a higher priority than the applied GroupDescriptors (added either by code or by dragging columns to the group panel).

Custom grouping is applied if user grouping is enabled through the RadGridView.EnableGrouping or GridViewTemplate.EnableGrouping properties. By default, grouping is enabled at all levels.

RadGridView provides two mechanisms for custom grouping:

  • Handling the CustomGrouping event
  • Replacing the RadGridView grouping mechanism by providing a custom GroupPredicate

You can use the GroupSummaryEvaluate event to format the group header row text of the created custom groups.

Using the CustomGrouping event

The CustomGrouping event is fired if custom grouping is enabled through the RadGridView.EnableCustomGrouping or GridViewTemplate.EnableCustomGrouping properties. By default, custom grouping is disabled at all levels.

  • Template – the template that holds the rows that will be grouped
  • Row – the row which group is defined
  • Level – the level of the current group, represents zero-based depth of the group
  • GroupKey – identifier of the group
  • Handled – defines whether the row is processed by the custom algorithm or by the applied group descriptors.

The following example demonstrates how to handle the CustomGrouping event to group the RadGridView rows by the values of the Country column creating groups only for predefined countries:

Copy[C#]
this.radGridView1.EnableCustomGrouping = true;
this.radGridView1.CustomGrouping += new GridViewCustomGroupingEventHandler(radGridView1_CustomGrouping);

GroupDescriptor descriptor = new GroupDescriptor("Country");
this.radGridView1.GroupDescriptors.Add(descriptor);

this.radGridView1.GroupSummaryEvaluate += new GroupSummaryEvaluateEventHandler(radGridView1_GroupSummaryEvaluate);
Copy[C#]
private void radGridView1_CustomGrouping(object sender, GridViewCustomGroupingEventArgs e)
{
    string country = e.Row.Cells["Country"].Value.ToString();
    switch (country)
    {
        case "USA":
            e.GroupKey = "1. USA";
            break;
        case "Japan":
            e.GroupKey = "2. Japan";
            break;
        case "Germany":
            e.GroupKey = "3. Germany";
            break;
        default:
            e.GroupKey = "Other country";
            break;
    }
}

private void radGridView1_GroupSummaryEvaluate(object sender, GroupSummaryEvaluationEventArgs e)
{
    if (e.Value == null)
    {
        e.FormatString = e.Group.Key.ToString();
    }
}
Copy[VB.NET]
Me.RadGridView1.EnableCustomGrouping = True

Dim descriptor As New GroupDescriptor("Country")
Me.RadGridView1.GroupDescriptors.Add(descriptor)
Copy[VB.NET]
Private Sub RadGridView1_CustomGrouping(ByVal sender As Object, ByVal e As Telerik.WinControls.UI.GridViewCustomGroupingEventArgs) Handles RadGridView1.CustomGrouping
    Dim country As String = e.Row.Cells("Country").Value.ToString()
    Select Case country
        Case "USA"
            e.GroupKey = "1. USA"
            Exit Select
        Case "Japan"
            e.GroupKey = "2. Japan"
            Exit Select
        Case "Germany"
            e.GroupKey = "3. Germany"
            Exit Select
        Case Else
            e.GroupKey = "Other country"
            Exit Select
    End Select
End Sub

Private Sub RadGridView1_GroupSummaryEvaluate(ByVal sender As Object, ByVal e As Telerik.WinControls.UI.GroupSummaryEvaluationEventArgs) Handles RadGridView1.GroupSummaryEvaluate
    If e.Value Is Nothing Then
        e.FormatString = e.Group.Key.ToString()
    End If
End Sub
gridview-grouping-custom-grouping 001

Implementing grouping mechanism by using GroupPredicate

You can replace the grouping mechanism in RadGridView with a custom one by setting the GroupPredicate of the GridViewTemplate.

The following example demonstrates how to use a custom grouping mechanism in RadGridView to group the rows by the values of the ContactTitle column, creating groups only for the desired contact title categories:

Copy[C#]
GroupDescriptor descriptor = new GroupDescriptor("ContactTitle");
this.radGridView1.GroupDescriptors.Add(descriptor);

this.radGridView1.MasterTemplate.GroupPredicate = new GroupPredicate<GridViewRowInfo>(PerformGrouping);
this.radGridView1.GroupSummaryEvaluate += new GroupSummaryEvaluateEventHandler(radGridView1_GroupSummaryEvaluate);
Copy[C#]
private object PerformGrouping(GridViewRowInfo row, int level)
{
    string title = row.Cells["ContactTitle"].Value.ToString();
    string groupKey;
    if (title.StartsWith("Sales"))
    {
        groupKey = "1. Sales contacts";
    }
    else if (title.StartsWith("Marketing"))
    {
        groupKey = "2. Marketing contacts";
    }
    else if (title.StartsWith("Accounting"))
    {
        groupKey = "3. Accounting contacts";
    }
    else
    {
        groupKey = "Other contacts";
    }

    return groupKey;
}

private void radGridView1_GroupSummaryEvaluate(object sender, GroupSummaryEvaluationEventArgs e)
{
    if (e.Value == null)
    {
        e.FormatString = e.Group.Key.ToString();
    }
}
Copy[VB.NET]
Dim descriptor As New GroupDescriptor("ContactTitle")
Me.RadGridView1.GroupDescriptors.Add(descriptor)
Me.RadGridView1.MasterTemplate.GroupPredicate = New GroupPredicate(Of GridViewRowInfo)(AddressOf PerformGrouping)
Copy[VB.NET]
Private Function PerformGrouping(ByVal row As GridViewRowInfo, ByVal level As Integer) As Object
    Dim title As String = row.Cells("ContactTitle").Value.ToString()
    Dim groupKey As String
    If title.StartsWith("Sales") Then
        groupKey = "1. Sales contacts"
    ElseIf title.StartsWith("Marketing") Then
        groupKey = "2. Marketing contacts"
    ElseIf title.StartsWith("Accounting") Then
        groupKey = "3. Accounting contacts"
    Else
        groupKey = "Other contacts"
    End If

    Return groupKey
End Function

Private Sub RadGridView1_GroupSummaryEvaluate(ByVal sender As Object, ByVal e As Telerik.WinControls.UI.GroupSummaryEvaluationEventArgs) Handles RadGridView1.GroupSummaryEvaluate
    If e.Value Is Nothing Then
        e.FormatString = e.Group.Key.ToString()
    End If
End Sub
gridview-grouping-custom-grouping 002