Background:
Arrow buttons for expansion/collapse are actually C1ExpanderButton that are part of C1Expander element present in each category. C1Expander has property IsExpanded that defines whether a category is expanded or collapsed.
So, access these C1Expander through C1PropertyGrid’s CategoryContainers and set the IsExpanded property for the specific category
Steps to Complete:
private void SetGroupState(C1PropertyGrid propGrd, string grpName, GroupState grpState) { foreach(KeyValuePair kvp in propGrd.CategoryContainers.Where(x=>x.Key== grpName)) { C1Expander expander = kvp.Value; if(expander != null) { if(grpState == GroupState.Expanded) expander.IsExpanded = true; else expander.IsExpanded = false; } } } public enum GroupState { Expanded = 0, Collapsed }