By default NativeWindow loads some where on the screen. Loading an splash screen or application on center of the screen will gives better user experience.

Below code we are creating a native window and aligning in the screen center.

var _splashWindow:NativeWindow = new NativeWindow(nativeWindowOptions);

_splashWindow.width = 484;

_splashWindow.height = 289;

_splashWindow.stage.align = "TL";

_splashWindow.stage.scaleMode = "noScale";

_splashWindow.title = "Center on screen";
var screenBounds:Rectangle = Screen.mainScreen.bounds;

_splashWindow.x = (screenBounds.width - _splashWindow.width)/2;

_splashWindow.y = (screenBounds.height - _splashWindow.height)/2;
_splashWindow.activate();

Here,

var screenBounds:Rectangle = Screen.mainScreen.bounds;

Screen.mainScreen.bounds return the screen boundary.

_splashWindow.x = (screenBounds.width - _splashWindow.width)/2;

_splashWindow.y = (screenBounds.height - _splashWindow.height)/2;

Centering the application on screen.