<Page
…
xmlns:ig="http://schemas.infragistics.com/xaml"
xmlns:igPrim="http://schemas.infragistics.com/xaml/primitives"
…>
<Button
Content="Sort By Category"
ig:Commanding.CommandTarget="{Binding ElementName=xamPropertyGrid1}">
<ig:Commanding.Command>
<igPrim:PropertyGridCommandSource
EventName="Click"
CommandType="SortByCategory" />
</ig:Commanding.Command>
</Button>