自动颤动的效果

Question

下午好，

我正在尝试从代码运行测试应用程序

当我扩展 State 时，它​​会在代码调用中给出错误，而当我扩展 StatelessWidget 时，它不会在调用中给出错误，但它在我的 'StateMyApp' 中出现错误。 coloquei State Myapp mais é 。 Quando eu coloco entre as <>一些

我在哪里调用代码

return Stack(
     fit: StackFit.loose,
     children: [
    PlaceholderHorarioMarcacoes(),

添加 StatelessWidget 时出错

class MyApp extends StatefulWidget {
  @override
  PlaceholderHorarioMarcacoes createState() => PlaceholderHorarioMarcacoes();
}

class PlaceholderHorarioMarcacoes extends StatelessWidget{
  String _timeString;

[给出状态时出错][3]

class MyApp extends StatefulWidget {
  @override
  PlaceholderHorarioMarcacoes createState() => PlaceholderHorarioMarcacoes();
}

class PlaceholderHorarioMarcacoes extends State<MyApp>{
  String _timeString;

}