Test existence of objects in a grid

Question

In my main window's xaml, I use a grid with 3 rows and 2 columns. I have fonctions that load different UserControls.

Problem, I can end up loading many times the same UserControl in the grid, in the same cell.

I tried to create a test to verify that the cell in the grid is empty, but it is not working.

Could anybody help please?

P.S., I have only just begun programming in WPF, though I have some knowledge in C# and xml.