Redux：React Nativeにおける状態管理パターンの解説

import { configureStore } from '@reduxjs/toolkit'

interface CounterState {
  value: number
}

const initialState: CounterState = { value: 0 }

function counterReducer(
  state = initialState,
  action: { type: string }
): CounterState {
  switch (action.type) {
    case 'INCREMENT':
      return { value: state.value + 1 }
    default:
      return state
  }
}

const store = configureStore({ reducer: counterReducer })
store.dispatch({ type: 'INCREMENT' })
console.log(store.getState()) // { value: 1 }

import { createAsyncThunk } from '@reduxjs/toolkit'

export const fetchUser = createAsyncThunk(
  'users/fetchById',
  async (userId: number, { rejectWithValue }) => {
    const response = await fetch(`/api/users/${userId}`)
    if (!response.ok)
      return rejectWithValue('Failed to fetch')
    return await response.json()
  }
)

import { createSlice, PayloadAction } from '@reduxjs/toolkit'

const counterSlice = createSlice({
  name: 'counter',
  initialState: { value: 0 },
  reducers: {
    increment(state) { state.value += 1 },
    incrementByAmount(state, action: PayloadAction<number>) {
      state.value += action.payload
    }
  }
})

export const { increment, incrementByAmount } = counterSlice.actions
export default counterSlice.reducer