# mapDispatchToProps

`mapDispatchToProps`是`connect`函数的第二个参数，用来建立 UI 组件的参数到`store.dispatch`方法的映射。也就是说，它定义了哪些用户的操作应该当作 Action，传给 Store。它可以是一个函数，也可以是一个对象。

`mapDispatchToProps`是`connect`函数的第二个参数，用来建立 UI 组件的参数到`store.dispatch`方法的映射。也就是说，它定义了哪些用户的操作应该当作 Action，传给 Store。它可以是一个函数，也可以是一个对象。

```javascript
const mapDispatchToProps = (
  dispatch,
  ownProps
) => {
  return {
    onClick: () => {
      dispatch({
        type: 'SET_VISIBILITY_FILTER',
        filter: ownProps.filter
      });
    }
  };
}
```

从上面代码可以看到，`mapDispatchToProps`作为函数，应该返回一个对象，该对象的每个键值对都是一个映射，定义了 UI 组件的参数怎样发出 Action。

如果`mapDispatchToProps`是一个对象，它的每个键名也是对应 UI 组件的同名参数，键值应该是一个函数，会被当作 Action creator ，返回的 Action 会由 Redux 自动发出。举例来说，上面的`mapDispatchToProps`写成对象就是下面这样。

```javascript
const mapDispatchToProps = {
  onClick: (filter) => {
    type: 'SET_VISIBILITY_FILTER',
    filter: filter
  };
}
```


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