public object GetMasterRowKeyValue()

Public Function GetMasterRowKeyValue As Object

protected void detailGrid_BeforePerformDataSelect(object sender, EventArgs e) {
    Session["CategoryID"] = (sender as ASPxGridView).GetMasterRowKeyValue();
}

Protected Sub detailGrid_BeforePerformDataSelect(ByVal sender As Object,_
ByVal e As System.EventArgs) Handles ASPxGridView1.BeforePerformDataSelect
    Session("CategoryID") = CType(sender, ASPxGridView).GetMasterRowKeyValue()
End Sub

<dx:ASPxGridView ID="ASPxGridView1" runat="server" AutoGenerateColumns="False" Width="511px">
    <Columns>
        <dx:GridViewDataTextColumn FieldName="ID" />
        <dx:GridViewDataTextColumn FieldName="ParentID" />
        <dx:GridViewDataTextColumn FieldName="Name" />
    </Columns>
    <SettingsDetail ShowDetailRow="True" />
    <Templates>
        <DetailRow>
            <dx:ASPxGridView ID="ASPxGridView2" runat="server" AutoGenerateColumns="False"
                KeyFieldName="ID" OnDataBinding="ASPxGridView2_DataBinding">
                <Columns>
                    <dx:GridViewDataTextColumn FieldName="ID" />
                    <dx:GridViewDataTextColumn FieldName="ParentID" />
                    <dx:GridViewDataTextColumn FieldName="Name" />
                </Columns>
                <SettingsDetail IsDetailGrid="True" />
            </dx:ASPxGridView>
        </DetailRow>
    </Templates>
</dx:ASPxGridView>

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using DevExpress.Web.ASPxGridView;

public partial class _Default : System.Web.UI.Page {
    DataSet ds;
    DataTable table;

    protected void Page_Load(object sender, EventArgs e) {
        ds = new DataSet();
        table = ds.Tables.Add("People");
        table.Columns.Add("ID", typeof(int));
        table.Columns.Add("ParentID", typeof(int));
        table.Columns.Add("Name", typeof(string));
        table.PrimaryKey = new DataColumn[] { table.Columns["ID"] };

        table.Rows.Add(new object[] { 1, DBNull.Value, "Bill" }) ;
        table.Rows.Add(new object[] { 2, DBNull.Value, "John" });
        table.Rows.Add(new object[] { 3, DBNull.Value, "Clive" });
        table.Rows.Add(new object[] { 4, 1, "Ann" });
        table.Rows.Add(new object[] { 5, 1, "Tom" });
        table.Rows.Add(new object[] { 6, 3, "Jane" });

        ds.Relations.Add("ParentChildren", table.Columns["ID"], table.Columns["ParentID"]);

        DataView dv = new DataView(table);
        dv.RowFilter = "[ParentID] Is Null";

        ASPxGridView1.KeyFieldName = "ID";
        ASPxGridView1.DataSource = dv;
        ASPxGridView1.DataBind();
    }

    protected void ASPxGridView2_DataBinding(object sender, EventArgs e) {
        ASPxGridView detailGrid = (ASPxGridView)sender;
        object id = detailGrid.GetMasterRowKeyValue();
        DataView detailData = new DataView(table);
        detailData.RowFilter = String.Format("[ParentID] = {0}", id);
        detailGrid.DataSource = detailData;
    }
}

Imports Microsoft.VisualBasic
Imports System
Imports System.Data
Imports System.Configuration
Imports System.Web
Imports System.Web.Security
Imports System.Web.UI
Imports System.Web.UI.WebControls
Imports System.Web.UI.WebControls.WebParts
Imports System.Web.UI.HtmlControls
Imports DevExpress.Web.ASPxGridView

Partial Public Class _Default
    Inherits System.Web.UI.Page
    Private ds As DataSet
    Private table As DataTable

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)
        ds = New DataSet()
        table = ds.Tables.Add("People")
        table.Columns.Add("ID", GetType(Integer))
        table.Columns.Add("ParentID", GetType(Integer))
        table.Columns.Add("Name", GetType(String))
        table.PrimaryKey = New DataColumn() { table.Columns("ID") }

        table.Rows.Add(New Object() { 1, DBNull.Value, "Bill" })
        table.Rows.Add(New Object() { 2, DBNull.Value, "John" })
        table.Rows.Add(New Object() { 3, DBNull.Value, "Clive" })
        table.Rows.Add(New Object() { 4, 1, "Ann" })
        table.Rows.Add(New Object() { 5, 1, "Tom" })
        table.Rows.Add(New Object() { 6, 3, "Jane" })

        ds.Relations.Add("ParentChildren", table.Columns("ID"), table.Columns("ParentID"))

        Dim dv As DataView = New DataView(table)
        dv.RowFilter = "[ParentID] Is Null"

        ASPxGridView1.KeyFieldName = "ID"
        ASPxGridView1.DataSource = dv
        ASPxGridView1.DataBind()
    End Sub

    Protected Sub ASPxGridView2_DataBinding(ByVal sender As Object, ByVal e As EventArgs)
        Dim detailGrid As ASPxGridView = CType(sender, ASPxGridView)
        Dim id As Object = detailGrid.GetMasterRowKeyValue()
        Dim detailData As DataView = New DataView(table)
        detailData.RowFilter = String.Format("[ParentID] = {0}", id)
        detailGrid.DataSource = detailData
    End Sub
End Class

ASPxGridView detailGridView = (ASPxGridView)sender;
dv.RowFilter = "MasterID = " + detailGridView.GetMasterRowKeyValue();
detailGridView.DataSource = dv;

cmd.Parameters.Add("@SupplierID", SqlDbType.Int).Value = randomizer.Next(1, 29);
cmd.Parameters.Add("@CategoryID", SqlDbType.Int).Value = senderGridView.GetMasterRowKeyValue();
cmd.Parameters.Add("@UnitPrice", SqlDbType.Decimal).Value = e.NewValues["UnitPrice"];

ASPxGridView grid = sender as ASPxGridView;
int masterKey = (int)grid.GetMasterRowKeyValue();
grid.DataSource = DataContext.Products.Where(p => p.CategoryID == masterKey).ToList();

ASPxGridView detailGrid = (ASPxGridView)sender;
int id = (int)detailGrid.GetMasterRowKeyValue();

Dim detailGridView As ASPxGridView = CType(sender, ASPxGridView)
dv.RowFilter = "MasterID = " & detailGridView.GetMasterRowKeyValue()
detailGridView.DataSource = dv

cmd.Parameters.Add("@SupplierID", SqlDbType.Int).Value = randomizer.Next(1, 29)
cmd.Parameters.Add("@CategoryID", SqlDbType.Int).Value = senderGridView.GetMasterRowKeyValue()
cmd.Parameters.Add("@UnitPrice", SqlDbType.Decimal).Value = e.NewValues("UnitPrice")

Dim grid As ASPxGridView = TryCast(sender, ASPxGridView)
Dim masterKey As Integer = CInt(grid.GetMasterRowKeyValue())
grid.DataSource = DataContext.Products.Where(Function(p) p.CategoryID = masterKey).ToList()

Dim detailGrid As ASPxGridView = CType(sender, ASPxGridView)
Dim id As Integer = CInt(detailGrid.GetMasterRowKeyValue())
Dim result = From q In ChildData Where q.ParentID = id Select q