React Native: Possible unhandled promise rejection
React NativeReact Native Problem Overview
I'm getting the following error:
>Possible unhandled promise rejection (id:0: Network request failed)
Here's the promise code, I don't see what's wrong here, any ideas?
return fetch(url)
.then(function(response){
return response.json();
})
.then(function(json){
return {
city: json.name,
temperature: kelvinToF(json.main.temp),
description: _.capitalize(json.weather[0].description)
}
})
.catch(function(error) {
console.log('There has been a problem with your fetch operation: ' + error.message);
});
}
Edit:
I added a catch function and got a better error:
>You passed an undefined or null state object; instead, use forceUpdate(). index.ios.js:64 undefined
Here's the index.ios.js code. The url is fine and giving me the correct json data. I can see with console log that both region.latitude
and region.longitude
are available in Api(region.latitude, region.longitude)
. But data
is undefined.
I'm still not sure what's going on, why there's a problem with data
and why it's undefined.
// var React = require('react-native'); --deprecated
// updated
import React from 'react';
// updated
import {
AppRegistry,
MapView,
View,
Text,
StyleSheet,
} from 'react-native';
/*
var {
AppRegistry,
MapView,
View,
Text,
StyleSheet
} = React;
*/ // -- depreciated
var Api = require('./src/api');
var Weather = React.createClass({
getInitialState: function() {
return {
pin: {
latitude: 0,
longitude: 0
},
city: '',
temperature: '',
description: ''
};
},
render: function() {
return <View style={styles.container}>
<MapView
annotations={[this.state.pin]}
onRegionChangeComplete={this.onRegionChangeComplete}
style={styles.map}>
</MapView>
<View style={styles.textWrapper}>
<Text style={styles.text}>{this.state.city}</Text>
<Text style={styles.text}>{this.state.temperature}</Text>
<Text style={styles.text}>{this.state.description}</Text>
</View>
</View>
},
onRegionChangeComplete: function(region) {
this.setState({
pin: {
longitude: region.longitude,
latitude: region.latitude
}
});
Api(region.latitude, region.longitude)
.then((data) => {
console.log(data);
this.setState(data);
});
}
});
var styles = StyleSheet.create({
container: {
flex: 1,
justifyContent: 'center',
alignItems: 'stretch',
backgroundColor: '#F5FCFF'
},
map: {
flex: 2,
marginTop: 30
},
textWrapper: {
flex: 1,
alignItems: 'center'
},
text: {
fontSize: 30
}
});
AppRegistry.registerComponent('weather', () => Weather);
React Native Solutions
Solution 1 - React Native
catch function in your api should either return some data which could be handled by Api call in React class or throw new error which should be caught using a catch function in your React class code. Latter approach should be something like:
return fetch(url)
.then(function(response){
return response.json();
})
.then(function(json){
return {
city: json.name,
temperature: kelvinToF(json.main.temp),
description: _.capitalize(json.weather[0].description)
}
})
.catch(function(error) {
console.log('There has been a problem with your fetch operation: ' + error.message);
// ADD THIS THROW error
throw error;
});
Then in your React Class:
Api(region.latitude, region.longitude)
.then((data) => {
console.log(data);
this.setState(data);
}).catch((error)=>{
console.log("Api call error");
alert(error.message);
});
Solution 2 - React Native
You should add the catch() to the end of the Api call. When your code hits the catch() it doesn't return anything, so data is undefined when you try to use setState() on it. The error message actually tells you this too :)
Solution 3 - React Native
According to this post, you should enable it in XCode.
- Click on your project in the Project Navigator
- Open the Info tab
- Click on the down arrow left to the "App Transport Security Settings"
- Right click on "App Transport Security Settings" and select Add Row
- For created row set the key “Allow Arbitrary Loads“, type to boolean and value to YES.
Solution 4 - React Native
Adding here my experience that hopefully might help somebody.
I was experiencing the same issue on Android emulator in Linux with hot reload. The code was correct as per accepted answer and the emulator could reach the internet (I needed a domain name).
Refreshing manually the app made it work. So maybe it has something to do with the hot reloading.
Solution 5 - React Native
In My case, I am running a local Django backend in IP 127.0.0.1:8000
with Expo start.
Just make sure you have the server in public domain
not hosted lcoally on your machine
Solution 6 - React Native
delete build folder projectfile\android\app\build
and run project