Hello Alexander,

I was able to see that rows keep their expanded state by default on post back. I have used below mark up and code to test the behavior you described: 

<ig:WebHierarchicalDataGrid ID="WebHierarchicalDataGrid1" runat="server" Height="350px"          Width="400px" DataKeyFields="ID" AutoGenerateBands="False" AutoGenerateColumns="False" InitialDataBindDepth="0">
<Columns>
 <ig:BoundDataField DataFieldName="ID" Header-Text="ID" Key="ID">                     </ig:BoundDataField>
<ig:BoundDataField DataFieldName="NumEditorID" Header-Text="NumEditorID" Key="NumEditorID" ></ig:BoundDataField>
</Columns>
<Bands>
<ig:Band DataMember="Locals" Key="Locals" AutoGenerateColumns="false"  DataKeyFields="ModID">
<Columns>
<ig:BoundDataField DataFieldName="ModID" Header-Text="ModID" Key="ModID" >
</ig:BoundDataField>
</Columns></ig:Band></Bands>
</ig:WebHierarchicalDataGrid>

protected void Page_Load(object sender, EventArgs e)
{
if (Session["data"] == null)
{
Session["data"] = GetEmployDepartmentDataSet();
}
this.WebHierarchicalDataGrid1.DataSource = Session["data"];
}
private DataSet GetEmployDepartmentDataSet()
{
DataSet ds = new DataSet("EmployeeRecords");
// Get the tables to use in the DataSet
DataTable Employees = new DataTable("Employess");
Employees.Columns.Add("ID", typeof(int));
Employees.Columns.Add("NumEditorID", typeof(int));
for (int i = 0; i < 10; i++)
{
Employees.Rows.Add(new object[] { i, i+i });
}
Employees.PrimaryKey = new DataColumn[] { Employees.Columns[0] };
DataTable Locals = new DataTable("Locals");
Locals.Columns.Add("ModID", typeof(int));
for (int i = 0; i < 10; i++)
{
Locals.Rows.Add(new object[] { i});
}
Locals.PrimaryKey = new DataColumn[] { Locals.Columns[0] };
// Add the tables to the DataSet
ds.Tables.Add(Employees);
ds.Tables.Add(Locals);
// Create the relationship between the tables.
ds.Relations.Add("DepartmentEmployee", Employees.Columns["ID"], Locals.Columns["ModID"]);
return ds;
}

However, you may write below lines of code that will keep the state of expanded grid:

if (this.WebHierarchicalDataGrid1.GridView.Rows.Count > 0)
{
foreach (ContainerGridRecord rec in this.WebHierarchicalDataGrid1.GridView.Rows)
{
if (rec.Expanded == true)
{ rec.ExpandChildren(); }}}

I hope this helps.

We had faced issues too where grid rowCounts and rows collection were not in sync. Due to which we started using grid.Rows.Clear().

did you say there was some workaround for grid.Rows.Clear() then? Because I have a similar issue with sorting child bands in WHDG and I use row clearing.

Thank you, David, Bhadresh!

You are right, I did Rows.Clear() to refresh data after postback.

On postpack the data binded to the grid is modified, but unfortunately simple grid.DataBind()  doesn't reflect the changes. So I have to do Rows.Clear().

In any case, I've workaround the problem. Thanks for clarification.

Alexander