如何绑定动态创建的扩展器的isexpanded属性

this is my first entry, so please be patient with me. My problem is that i have Expanders inside a DataGrid. The Expanders are used for Grouping. I also have a filter textfield which filters the View and shows only the matching lines. My problem is: the Grouping expanders isexpanded property should be true when the search finds entries and false if the search is not used. This is my DataGrid.GroupStyle:this is my first entry, so please be patient wi