我想创建一个加载器数据，在数据加载结束时屏幕将自动更改屏幕（使用导航器）。
但我有一些问题。
Unhandled Exception: NoSuchMethodError: The method 'ancestorStateOfType' was called on null.
在“getDataOfUser()”方法结束时，“print(a)”执行得很好，但是当它尝试更改屏幕时它崩溃了，我有这个错误：
E/flutter (32148): [ERROR:flutter/lib/ui/ui_dart_state.cc(148)] Unhandled Exception: NoSuchMethodError: The method 'ancestorStateOfType' was called on null.
E/flutter (32148): Receiver: null
E/flutter (32148): Tried calling: ancestorStateOfType(Instance of 'TypeMatcher<NavigatorState>')
E/flutter (32148): #0 Object.noSuchMethod (dart:core-patch/object_patch.dart:50:5)
E/flutter (32148): #1 Navigator.of (package:flutter/src/widgets/navigator.dart:1446:19)
E/flutter (32148): #2 LoginScreenPresenter.initState.<anonymous closure> (package:test_app/login_presenter.dart:35:17)
Unhandled Exception: NoSuchMethodError: The method 'ancestorStateOfType' was called on null.