ISVisible Property

Hi folks,

here my problem:

i have this xaml

behind it this piece of code available when i click a button

GridAct.IsVisible = true;
viewModel.RicalculateList();
GridAct.IsVisible = false;

the grid is not visible andthe property is true only when i change the code in this way

Device.BeginInvokeOnMainThread(() => {
//API calls to load lists

GridAct.IsVisible = true;
});

viewModel.RicalculateList();
GridAct.IsVisible = false;

but if i try to put the other two lines inside nothing works

advices...