We already answered your support ticket on the subject. For convenience we will paste our answer here as well:
Indeed the sample project does not implement what you are looking for, it is just the description my colleague gave. I will try to explain in details.
First of all you need to store all expanded groups - RadGridView.GroupRowIsExpanded is the perfect event for that. Indeed the code pasted below is not the "full" solution, since one group could be expanded and collapsed several times. You will need to handle all the possible cases.
Then you should expand the saved groups one by one.
this.radGridView.GroupRowIsExpandedChanged += new EventHandler<
> expandedGroups = new List<
void radGridView_GroupRowIsExpandedChanged(object sender, Telerik.Windows.Controls.GridView.GroupRowEventArgs e)
the Telerik team