Gridsplitter in combination with Scrollviewer

Hello,

Ich have a Grid with 3 Rows, the Grid is in a Scrollviewer. The second row is a Gridsplitter, when i move the Gridsplitter one row gets bigger the other shorter. What i need is that the Gridsplitter makes the row bigger without changing the Height of the other one, in order to scroll the whole grid with the Scrollviewer.

Does anyone has an Idea how to make that possible?

Thanks a lot.