react-redux的一个问题

Question

const mapStateToProps = (state) => ({   todos: getVisibleTodos(state.todos, state.visibilityFilter) })官方案例TODOS中 state.todos state.visibilityFilter是怎么来的？const visibilityFilter = (state = 'SHOW_ALL', action) => {  switch (action.type) {    case 'SET_VISIBILITY_FILTER':       return action.filter    default:      return state   } }export default visibilityFilter是reducer里的这个方法吗const todoApp = combineReducers({   todos,   visibilityFilter })然后state.visibilityFilter可以直接取到state值show_all?