How to insert a new row at the given position in a Grid?

Question

Hi,everyone. I have got a problem when used the Grid.RowDefinitions.Insert() method to add a new row at a given position. Each time I used the Insert(int index, RowDefinition value) method,it only added a new row at the last!The first parameter(index) seems to do not work! How can I do this? or is there any other property should to be set before uses this method? could you help me? Thank you!