React Native Fetch does not render response until after clicking screen

问题

So I've been building an app that uses the Fetch API to make a request. Unfortunately, I think the code shown in the Facebook docs are (may be?) incorrect.

Problem

When starting the app, Fetch makes a call to a URL to pull JSON data.

componentDidMount(){
 return fetch(REQUEST_URL)
  .then((response) => response.json())
  .then((responseJson) => {
    this.setState({
      isLoading: false,
      data: JSON.stringify(responseJson)
    })
  })
  .catch((error) => {
    console.error(error);
  });
}

This is similar to the code that Facebook docs give as an example.

The problem is that when I start the app, the data doesn't render in the render function.

render() {

 if (this.state.isLoading) {
   return (
    <View style={{flex: 1, paddingTop: 20}}>
      <ActivityIndicator />
    </View>
  );
 } 

var data = this.state.data;
return this.renderData(data); 
}

At least, it doesn't render until after I click/touch the screen. Once I touch the screen, the data renders. Otherwise, it just stays in a perpetual "loading" state.

Solution?

I remembered that sometime in the past, I had to bind event handlers to their respective controls (this.handleClick = this.handleClick.bind(this), for example)

And that got me thinking: Where is this in the promise request? Where does this point to?

componentDidMount(){
 return fetch(REQUEST_URL)
  .then((response) => response.json())
  .then((responseJson) => {
    this.setState({ <--- **Where are you going?**
      isLoading: false,
      data: JSON.stringify(responseJson)
    })
  })

I console.logged "this" within the responseJson promise, and it does point to the component, but I'm not convinced. With it being buried inside of the promise, I don't think the this.setState function is actually able to set the component's State.

So I made a variable before the fetch request.

const that = this;
return fetch(REQUEST_URL)

.then((response) => response.json())
.then((responseJson) => {

  that.setState({

    isLoading: false,
    data: JSON.stringify(responseJson)
  })
})

Now I'm not a software guru. I've been teaching myself this stuff for the last couple of years, so my logic is off half the time.

So if my reasoning is correct or incorrect, please let me know! What I do know is that this is working for me; once the data is fetched, it automatically sets the state and reloads, showing me the JSON data when rendered.

Any thoughts? Am I completely off here? Am I missing anything?

回答1:

I saw a problem like yours. It's not about your code. Are using the app in the Remote JS debugging mode? If so, disable it. If it didn't work, try to install a release version.

回答2:

(Posted on behalf of the OP).

Apparently it was due to running the app in debug mode. Running the app with this.setState works just fine when not in debug mode.

来源：https://stackoverflow.com/questions/44867336/react-native-fetch-does-not-render-response-until-after-clicking-screen

标签

javascript

react-native

fetch-api