What is the use of the ownProps arg in mapStateToP

问题:

I see that the mapStateToProps and mapDispatchToProps function which are passed to the connect function in Redux take ownProps as a second argument.

[mapStateToProps(state, [ownProps]): stateProps] (Function):

[mapDispatchToProps(dispatch, [ownProps]): dispatchProps] (Object or Function):

What is the optional [ownprops] argument for?

I am looking for an additional example to make things clear as there is already one in the Redux docs

回答1:

If the ownProps parameter is specified, react-redux will pass the props that were passed to the component into your connect functions. So, if you use a connected component like this:

import ConnectedComponent from './containers/ConnectedComponent'

<ConnectedComponent
  value="example"
/>

The ownProps inside your mapStateToProps and mapDispatchToProps functions will be an object:

{ value: 'example' }

And you could use this object to decide what to return from those functions.

---

For example, on a blog post component:

// BlogPost.js
export default function BlogPost (props) {
  return <div>
    <h2>{props.title}</h2>
    <p>{props.content}</p>
    <button onClick={props.editBlogPost}>Edit</button>
  </div>
}

You could return Redux action creators that do something to that specific post:

// BlogPostContainer.js
import { bindActionCreators } from 'redux'
import { connect } from 'react-redux'
import BlogPost from './BlogPost.js'
import * as actions from './actions.js'

const mapStateToProps = (state, props) =>
  // Get blog post data from the store for this blog post ID.
  getBlogPostData(state, props.id)

const mapDispatchToProps = (dispatch, props) => bindActionCreators({
  // Pass the blog post ID to the action creator automatically, so
  // the wrapped blog post component can simply call `props.editBlogPost()`:
  editBlogPost: () => actions.editBlogPost(props.id)
}, dispatch)

const BlogPostContainer = connect(mapStateToProps, mapDispatchToProps)(BlogPost)
export default BlogPostContainer

Now you would use this component like so:

import BlogPostContainer from './BlogPostContainer.js'

<BlogPostContainer id={1} />

回答2:

ownProps refers to the props that were passed down by the parent.

So, for example:

Parent.jsx:

...
<Child prop1={someValue} />
...

Child.jsx:

class Child extends Component {
  props: {
    prop1: string,
    prop2: string,
  };
...
}

const mapStateToProps = (state, ownProps) => {
  const prop1 = ownProps.prop1;
  const tmp = state.apiData[prop1]; // some process on the value of prop1
  return {
    prop2: tmp
  };
};

回答3:

goto-bus-stop's answer is good, but one thing to remember is that, according to the author of redux, Abramov/gaearon, using ownProps in those functions makes them slower because they must rebind the action creators when the props change.

See his comment in this link: https://github.com/reduxjs/redux-devtools/issues/250