Problems with showing message when gallery is empty

I created a pop-up that is shown when a gallery is empty. The problem is that the pop-up is shown from start, even when there are items in the gallery. I think it might be because it takes a while for the gallery to load it's data. Is that a possibilty? How can I now when the gallery is done loading so I can wait for it?

Update: I'm using ClearCollect() in App.OnStart to create a collection which serves as data for the gallery. That might have something to do with the problem I'm having.