useEffect returns unhandled promise - react-native

Question

I have been for several hours trying to get an API to be called in ReactNative useEffect hook. Sometimes when I restart my app the value is resolved. But most of the time, I have an Unhandled promise rejection. I googled and tried various methods. I tried using .then etc.. I just can't figure it out.
import React, { useState, useContext, useEffect } from 'react';
import { View, Text, StyleSheet, TouchableOpacity, FlatList } from 'react-native';
import { EvilIcons } from '#expo/vector-icons';
import jsonServer from '../api/jsonServer';
const ShowScreen = ({ navigation }) => {
const id = navigation.getParam('id');
const [post, setPost] = useState([]);
const getBlog = async () => {
const result = await jsonServer.get(`http://0.0.0.0/blog/docroot/jsonapi/node/article/${id}`);
return result;
}
useEffect(() => {
async function setToState() {
const val = await getBlog();
setPost(val);
}
setToState();
},[]);
return (
<View>
<Text>Here { console.log(post) }</Text>
</View>
);
};
ShowScreen.navigationOptions = ({ navigation }) => {
return {
headerRight: (
<TouchableOpacity
onPress={() =>
navigation.navigate('Edit', { id: navigation.getParam('id')
})}
>
<EvilIcons name="pencil" size={35} />
</TouchableOpacity>
)
};
};
const styles = StyleSheet.create({});
export default ShowScreen;

Answer 1

What you could do is something like this:
....
....
const [post, setPost] = useState([]);
const [isMounted, setIsMounted] = useState(false);
const getBlog = async () => {
const result = await jsonServer.get(`http://0.0.0.0/blog/docroot/jsonapi/node/article/${id}`);
return result;
}
useEffect(() => {
setIsMounted(true)
async function setToState() {
// using try catch I'm handling any type of rejection from promises. All errors will move to catch block.
try{
const val = await getBlog();
// checking if component is still mounted. If mounted then setting a value. We shouldn't update state on an unmounted component.
if(isMounted){
setPost(val);
}
} catch(err){
console.log("Error", err)
}
}
setToState();
return () => {
// Setting is mounted to false as the component is unmounted.
setIsMounted(false)
}
},[]);
I believe this will solve your Unhandled promise rejection error. Please try if it still doesn't solve the issue will create the same in Sanck.

Answer 2

I think my issue was not just promise, the issue is also seems to be me not handling undefined/null in the state. The below code is working for me.
import React, { useState, useContext, useEffect } from 'react';
import { View, Text, StyleSheet, TouchableOpacity, FlatList } from 'react-native';
import { EvilIcons } from '#expo/vector-icons';
import jsonServer from '../api/jsonServer';
const ShowScreen = ({ navigation }) => {
const id = navigation.getParam('id');
const [post, setPost] = useState([]);
const getBlog = async () => {
const result = await jsonServer.get(`http://hello.com/jsonapi/node/article/${id}`).then(
res => {
setPost(res)
return res;
}, err => {
console.log(err);
});
}
useEffect(() => {
setPost(getBlog());
},[]);
return (
<View>
<Text>{ post.data ? post.data.data.id : "" }</Text>
</View>
);
};
export default ShowScreen;
Note: I am setting the state in useEffect as well as in the request. I am yet to check if I can just do it once.