Criando fatias com createSlice
Defina uma fatia com createSlice, declare o estado inicial e as funções redutoras e exporte os criadores de ações gerados automaticamente e o redutor.
Criando fatias com createSlice é uma aula grátis de React Native Academy no CoddyKit. Esta é a aula 2 de 4. Você pode ler a aula completa abaixo gratuitamente — depois pratica ao vivo no navegador com um editor de código integrado e um tutor de IA 24/7. Faz parte do caminho de aprendizado de React Native Academy, e seu progresso é sincronizado entre a web e o app CoddyKit. O curso de React Native Academy inclui 4 aulas no total.
Partes desta aula ainda não foram traduzidas e aparecem em inglês.
What Is a Redux Slice?
A slice is a self-contained piece of Redux logic for one feature of your app. It bundles the initial state, the reducer functions, and the auto-generated action creators together in a single file. The name comes from the idea that each slice represents a portion (slice) of the global Redux state tree.
Importing and Calling createSlice
createSlice is imported from @reduxjs/toolkit and accepts a configuration object with three required fields: name (a string prefix for action types), initialState (the starting value for this slice's state), and reducers (an object of reducer functions). It returns an object containing the slice reducer and the action creators.
import { createSlice } from '@reduxjs/toolkit';
const counterSlice = createSlice({
name: 'counter',
initialState: { value: 0 },
reducers: {},
});
export default counterSlice.reducer;Defining Reducer Functions
Each function you add to the reducers object becomes a case reducer that handles a specific action. RTK uses the Immer library under the hood, so you can write code that appears to mutate state directly — Immer converts it to an immutable update automatically. You never need to spread or copy the state object manually.
const counterSlice = createSlice({
name: 'counter',
initialState: { value: 0 },
reducers: {
increment(state) {
state.value += 1; // Immer makes this safe
},
decrement(state) {
state.value -= 1;
},
incrementByAmount(state, action) {
state.value += action.payload;
},
},
});Auto-Generated Action Creators
createSlice automatically generates an action creator for each reducer function you define. You export them from the slice and call them when dispatching. The action creator name matches the reducer key, and the generated action type string follows the pattern sliceName/reducerName, for example counter/increment.
export const { increment, decrement, incrementByAmount } = counterSlice.actions;
// Using in a component:
import { useAppDispatch } from '../../store/hooks';
import { increment } from './counterSlice';
const dispatch = useAppDispatch();
dispatch(increment()); // { type: 'counter/increment' }
dispatch(incrementByAmount(5)); // { type: 'counter/incrementByAmount', payload: 5 }Exporting the Reducer
The createSlice call returns an object with a reducer property. You export this as the default export and then import it in your store configuration. RTK composes all your slice reducers into the single root reducer automatically when you pass them to configureStore.
// counterSlice.ts
const counterSlice = createSlice({ /* ... */ });
export const { increment, decrement } = counterSlice.actions;
export default counterSlice.reducer;
// store/index.ts
import counterReducer from '../features/counter/counterSlice';
export const store = configureStore({
reducer: { counter: counterReducer },
});Defining TypeScript State Types
When using TypeScript, explicitly type your initialState so RTK can infer state and action types throughout the slice. Define an interface for your state and assign it as the type annotation on initialState. RTK will then infer the correct type for the state parameter in every reducer function automatically.
interface CounterState {
value: number;
status: 'idle' | 'loading' | 'failed';
}
const initialState: CounterState = {
value: 0,
status: 'idle',
};
const counterSlice = createSlice({
name: 'counter',
initialState,
reducers: {
increment(state) {
state.value += 1; // TypeScript knows state is CounterState
},
},
});Using PayloadAction for Typed Payloads
When a reducer receives data from the dispatched action, import PayloadAction from RTK to type the action parameter. PayloadAction<number> tells TypeScript that action.payload must be a number. This prevents accidental mismatches between what the action creator accepts and what the reducer expects.
import { createSlice, PayloadAction } from '@reduxjs/toolkit';
const counterSlice = createSlice({
name: 'counter',
initialState: { value: 0 },
reducers: {
incrementByAmount(state, action: PayloadAction<number>) {
state.value += action.payload;
},
},
});The prepare Callback
The prepare callback lets you customize the action creator before RTK dispatches the action. You use it when you need to generate an ID, format data, or add a timestamp to the payload. The object returned by prepare must have a payload field, and optionally meta and error fields.
import { nanoid } from '@reduxjs/toolkit';
const todosSlice = createSlice({
name: 'todos',
initialState: [],
reducers: {
addTodo: {
reducer(state, action: PayloadAction<{ id: string; text: string }>) {
state.push(action.payload);
},
prepare(text: string) {
return { payload: { id: nanoid(), text } };
},
},
},
});Resetting and Replacing State
Sometimes you need to reset a slice to its initial state — for example on user logout. You can return a completely new state value from a reducer instead of mutating. If you return a value, Immer uses it as the next state. This is the correct pattern for resetting or fully replacing state in a slice reducer.
const counterSlice = createSlice({
name: 'counter',
initialState: { value: 0, status: 'idle' },
reducers: {
reset() {
// Return the fresh initial value instead of mutating
return { value: 0, status: 'idle' };
},
},
});Responding to Actions from Other Slices
Slices can respond to actions defined in other slices using extraReducers. This avoids tight coupling — instead of importing one slice into another, you import only the action creator. Use the builder.addCase pattern to handle external action types inside your slice without adding them to the reducers key.
import { userSlice } from '../user/userSlice';
const cartSlice = createSlice({
name: 'cart',
initialState: { items: [] },
reducers: { /* own actions */ },
extraReducers: (builder) => {
builder.addCase(userSlice.actions.logout, (state) => {
state.items = []; // clear cart when user logs out
});
},
});Complete Counter Slice Example
Here is a complete, production-ready counter slice combining everything covered so far: a typed state interface, typed action creators with PayloadAction, and a reset action. Import this reducer into configureStore and its actions into components to have a fully working Redux feature.
import { createSlice, PayloadAction } from '@reduxjs/toolkit';
interface CounterState { value: number; }
const initialState: CounterState = { value: 0 };
export const counterSlice = createSlice({
name: 'counter',
initialState,
reducers: {
increment: (state) => { state.value += 1; },
decrement: (state) => { state.value -= 1; },
incrementByAmount: (state, action: PayloadAction<number>) => {
state.value += action.payload;
},
reset: () => initialState,
},
});
export const { increment, decrement, incrementByAmount, reset } = counterSlice.actions;
export default counterSlice.reducer;Quick Check
Test your understanding of React Native Mobile Development concepts from this lesson.
Lesson Recap
In this lesson you learned: createSlice bundles initial state, reducers, and action creators together, Immer lets you write mutating-style reducer code that stays immutable, and PayloadAction types the action payload for TypeScript safety. Next up we explore reading state with useSelector.
Perguntas Frequentes
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Defina uma fatia com createSlice, declare o estado inicial e as funções redutoras e exporte os criadores de ações gerados automaticamente e o redutor. Você pratica React Native Academy com código prático que executa diretamente no navegador, e um tutor de IA 24/7 responde suas dúvidas enquanto trabalha na aula.
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Todas as aulas deste curso
- Configurando o armazenamento e o Provider do Redux
- Criando fatias com createSlice
- Lendo o estado com useSelector
- Thunks assíncronos com createAsyncThunk