import TabStack from './TabStack'
    let MainStack = createStackNavigator({
        TabStack: TabStack,
        screenA: screenA,
        screenB: screenB

      },{
        headerMode: 'none',
        lazy:true,
        initialRouteName:'TabStack'
      });
export default createAppContainer(MainStack);

import { createBottomTabNavigator, createAppContainer } from 'react-navigation';

let TabStack = createBottomTabNavigator(
    {
        TabA: TabA,
        TabB: TabB,
    }
)
export default createAppContainer(TabStack);

let dispatch = StackActions.reset({
        index: 0,
        actions: [
            NavigationActions.navigate({ routeName: 'TabStack',
                action: NavigationActions.navigate({
                    routeName: 'TabB',
                  })
            }),
        ]
    })
    this.props.navigation.dispatch(dispatch)