Navigator is not working with this approach for navigating to another screen

[Rajakalla]

I wanted to Navigate to another screen. But it is throwing error.I am not understanding what to do now.Hoping quick response for my problem.

══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter (10712): The following assertion was thrown building StreamBuilder(dirty, state:
I/flutter (10712): _StreamBuilderBaseState<LoginScreenViewModel, AsyncSnapshot>#4385a):
I/flutter (10712): setState() or markNeedsBuild() called during build.
I/flutter (10712): This Overlay widget cannot be marked as needing to build because the framework is already in the
I/flutter (10712): process of building widgets. A widget can be marked as needing to be built during the build phase
I/flutter (10712): only if one of its ancestors is currently building. This exception is allowed because the framework
I/flutter (10712): builds parent widgets before children, which means a dirty descendant will always be built.
I/flutter (10712): Otherwise, the framework might not visit this widget during this build phase.
I/flutter (10712): The widget on which setState() or markNeedsBuild() was called was:
I/flutter (10712): Overlay-[LabeledGlobalKey#4f181](state: OverlayState#8bb69(entries:
I/flutter (10712): [OverlayEntry#c0a21(opaque: false; maintainState: false), OverlayEntry#3d106(opaque: false;
I/flutter (10712): maintainState: true), OverlayEntry#8b1fd(opaque: false; maintainState: false),
I/flutter (10712): OverlayEntry#a50bf(opaque: false; maintainState: true)]))
I/flutter (10712): The widget which was currently being built when the offending call was made was:
I/flutter (10712): StreamBuilder(dirty, state: _StreamBuilderBaseState<LoginScreenViewModel,
I/flutter (10712): AsyncSnapshot>#4385a)