为React函数组件创建新的MobX存储实例

Question

将MobX与React一起使用时，您可以在类组件实例上创建一个新的Store实例，如下所示：

const { extendObservable } = mobx;
const { Observer } = mobxReact;

class Store {
  constructor() {
    console.log("Created a store");
    extendObservable(this, {
      count: 0
    });
  }
}

class App extends React.Component {
  store = new Store();

  render() {
    const { store } = this;

    return (
      <Observer>
        {() => <button onClick={() => ++store.count}>{store.count}</button>}
      </Observer>
    );
  }
}

ReactDOM.render(<App />, document.getElementById("root"));

<script src="https://unpkg.com/react@16/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom@16/umd/react-dom.development.js"></script>
<script src="https://unpkg.com/[email protected]/lib/mobx.umd.min.js"></script>
<script src="https://unpkg.com/[email protected]/dist/index.min.js"></script>

<div id="root"></div>

将它转换为函数组件时，它仍然有效，但每次渲染都会创建一个新的Store实例，不会被使用。这不仅浪费，而且如果构造函数包含其他逻辑，则可能会产生不希望的行为。

const { extendObservable } = mobx;
const { observer, useObservable } = mobxReact;

class Store {
  constructor() {
    console.log("Created a store");
    extendObservable(this, {
      count: 0
    });
  }
}

const App = observer(() => {
  const store = useObservable(new Store());
  
  return <button onClick={() => ++store.count}>{store.count}</button>
});

ReactDOM.render(<App />, document.getElementById("root"));

<script src="https://unpkg.com/react@16/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom@16/umd/react-dom.development.js"></script>
<script src="https://unpkg.com/[email protected]/lib/mobx.umd.min.js"></script>
<script src="https://unpkg.com/[email protected]/dist/index.min.js"></script>

<div id="root"></div>

有没有办法在函数组件中的第一个渲染上创建一个单独的Store实例？

Answer 1

我们可以使用useObservable钩子而不是使用useState钩子，该钩子的函数返回一个新的Store作为参数。这个函数只会在第一次渲染时被调用一次，因此只能创建一个Store实例。

const { useState } = React;
const { extendObservable } = mobx;
const { observer, useObservable } = mobxReact;

class Store {
  constructor() {
    console.log("Created a store");
    extendObservable(this, {
      count: 0
    });
  }
}

const App = observer(() => {
  const [store] = useState(() => new Store());
  
  return <button onClick={() => ++store.count}>{store.count}</button>
});

ReactDOM.render(<App />, document.getElementById("root"));

<script src="https://unpkg.com/react@16/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom@16/umd/react-dom.development.js"></script>
<script src="https://unpkg.com/[email protected]/lib/mobx.umd.min.js"></script>
<script src="https://unpkg.com/[email protected]/dist/index.min.js"></script>

<div id="root"></div>