ListView's count property not updating when the ListView is inside a Drawer and the model gets its data from a network request

I have a ListView that is inside a Drawer and whose model gets its data from a network request.
Outside the drawer I have a button that opens the drawer and its text is set to the ListView's count property.
The problem is that the button's text is 0 (zero) until the drawer is opened. 
If I move the ListView outside the drawer the button's text is updated as expected.