Adding UIView on top of react native navigation

Question

I am using react-native-navigation and trying to add a native view on the top of everything. I initialized the Swift class in AppDelegate and call swift func:

func showUp() {
    let window = UIApplication.shared.keyWindow!
    let rect = UIView(frame: CGRect(x: 50, y: 50, width: 100, height: 50))
    rect.backgroundColor = UIColor.white
    window.addSubview(rect) }

The View seemed to be appeared while loading app and then disappears after app is loaded.

Thanks in advance)