如何在运行时更改子报表源？

I'm creating some report in C# and I have 2 types of them. The header and footer are the same but the middle part is different. I have a type parameter to determine which type report is it. But I don't know how to change the source subreport. The field "Use this report as subreport" unfortunately doesn't allow to enter the expression so I cannot define the necessary report by condition. And I don't know how to do that from the code.I'm creating some report in C# and I have 2 typ