如何使用 redux 更新全局狀態並從全局狀態中刪除項目

Question

我正在嘗試學習 redux，但我對如何正確使用我在行動中擁有的deleteCar概念感到deleteCar 。 減速器運行良好，但問題出在cars的全局狀態，如何更新 Car 組件中汽車的狀態，然后調用deleteCar函數並修改cars的狀態。 當我在Car組件中打印汽車狀態時，它是空的。

我有一個名為 Cars 的組件，它是 Car（單車）的父組件

import React from "react";
import Car from "../Car";
import { connect } from "react-redux";

class Cars extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      cars: []
    };
  }
  componentDidMount() {
    fetch(url)
      .then(response => response.json())
      .then(data => this.setState({ cars: data }));
  }
  render() {
    const { cars } = this.state;
    return (
      <div>
        {cars.map(c => (
          <Car key={c.id} make={c.make} price={c.price} id={c.id} />
        ))}
      </div>
    );
  }
}

const mapStateToProps = reduxStoreState => {
  return {
    cars: reduxStoreState.cars
  };
};

export default connect(mapStateToProps)(Cars);

單車

import React from "react";
import { deleteCar } from "../../actions/delete";
import { connect } from "react-redux";

const Car = ({ deleteCar, make, price, id }) => {
  return (
    <div className="card m-4">
      <div className="row">
        <div className="col">
          <h3>{make}</h3>
          <p>{price}</p>
        </div>
      </div>
      <div className="row">
        <button
          className="btn btn-danger"
          onClick={() =>
            deleteCar({
              id: id,
              make: make,
              price: price
            })
          }
        >
          Delete Car
        </button>
      </div>
    </div>
  );
};
const mapStateToProps = reduxStoreState => {
  return {
    cars: reduxStoreState.cars
  };
};

export default connect(mapStateToProps, { deleteCar })(Car);

行動

import { DELETE } from "../constants";
export const deleteCar = (payload) => {
  return {
    type: DELETE,
    payload: payload
  };
};

減速器

import { ADD, DELETE, EDIT } from "../constants";

export default function(state = { cars: [] }, action) {
  switch (action.type) {
    case ADD:
      return {
        ...state,
        cars: [...state.cars, action.payload]
      };
    case DELETE:
      return {
        ...state,
        cars: state.cars.filter(obj => obj !== action.payload)
      };
    case EDIT:
      return {
        ...state,
        cars: action.payload
      };
    default:
      return state;
  }
}

Answer 1

下面的代碼不會像你期望的那樣工作：

cars: state.cars.filter(obj => obj !== action.payload)

在 JavaScript 中，對象作為引用存儲在變量中。 通過像這樣調用刪除操作：

deleteCar({
  id: id,
  make: make,
  price: price
})

您每次都在創建一個新對象，因此它們永遠不會匹配並且不會被過濾。

看起來好像比較是這樣的：

{ id: id, make: make, price: price } === { id: id, make: make, price: price }

但實際上，它更像是這樣的比較：

// Both objects contain the same values
// But will not evaluate as equal because the references are different
'object_reference_1' === 'object_reference_2'

相反，我建議通過id檢查，如下所示：

cars: state.cars.filter(obj => obj.id !== action.payload.id)

---

第二個問題是您在Cars復制了 local 和 redux 狀態。

不使用本地狀態，而是調度一個操作來填充 redux。 它可能看起來像這樣：

componentDidMount() {
  fetch(url)
  .then(response => response.json())
  // Or preferably create a new action and call it like you did `deleteCar`
  .then(data => this.props.dispatch({ type: 'INITIALIZE', cars: data }));
}

然后在減速器中添加這種情況：

switch (action.type) {
  case 'INITIALIZE':
    return {
      ...state,
      cars: action.payload
    };

確保刪除cars的本地狀態並替換const { cars } = this.state; 使用this.props 。