如何在React Native中组织导航结构?

我正在使用react导航库。当前导航的组织方式如下:

应用程序js:

const Layout = createRootNavigator(signedIn);
return (
  <AppFontLoader>
    <Layout />
  </AppFontLoader>
);

应用导航器:

export const createRootNavigator = (signedIn = false) => {
  return createSwitchNavigator(
    {
      SignedIn: {
        screen: SignedIn
      },
      SignedOut: {
        screen: SignedOut
      }
    },
    {
      initialRouteName: signedIn ? "SignedIn" : "SignedOut"
    }
  );
};

应用导航器:

export const SignedIn = createMaterialBottomTabNavigator(
  {
    MeetingsScreen: {
...
}

会议屏幕:

const MeetingNavigator = createStackNavigator({
  MeetingsListScreen: {
    screen: MeetingsListScreen,
    navigationOptions: {
    }
  },
  AddMeetingForm: {
    screen: AddMeetingFormScreen
  },
  MeetingScreen: {
    screen: MeetingScreen
  }
}, {initialRouteName: "MeetingsListScreen"});

当前结构显示错误:

You should only render one navigator explicitly in your app, and other navigators should by rendered by including them in that navigator.

如何组织导航以便在屏幕之间移动更多的导航层?