I am using hooks in React Native. This is my code:
useEffect(() => {
if (var1.length > 0 ){
let sym = [];
var1.map((items) => {
let count = 0;
state.map((stateItems) => {
if(items === stateItems.name) {
count = count + 1;
}
})
if (count === 0) {
sym.push(items)
}
});
async function getAllStates (sym) {
let stateValues = [];
await Promise.all(sym.map(obj =>
axios.get(ServerURL + "/note?name=" + obj).then(response => {
stateValues.push(response.data[0]);
})
)).then(() =>{
setNewItem(stateValues);
});
}
getAllStates (sym);
}
}, [var1]);
useEffect(() => {
let stateValues = state;
for( let count = 0 ; count < newItem.length; count++ ){
stateValues.push(newItem[count]);
}
setState(stateValues);
}, [newItem]);
This runs successfully without any errors. However, when the state is displayed as below, I am not seeing the latest value added in the state. It shows all the previous values. When I refresh the whole application, I am able to see my value added.
return (
<View style={styles.container}>
<Text style = {{color:"white"}}>
{
state.map( (item, key) =>{
return(
<Text key = {key} style = {{color:"white"}}> {item.name} </Text>
)
})
}
</Text>
</View>
);
Can someone tell me why this is happening? I want to see the data render immediately after the axios call. I am using React Native.
when i force update using: stackoverflow.com/questions/53215285/... it works fine. However, i am looking for a better fix if anyone can provide?
This should do:
useEffect(() => {
var1.forEach(async (name) => {
if (state.some(item => item.name === name)) return;
const response = await axios.get(ServerURL + "/note?name=" + name);
setState(state => [...state, response.data[0]]);
});
}, [var1]);
I still see two issues in your approach:
this code may start the same ajax request multiple times before the result of the firstz ajax-request is added to state
; this also means that the result for the same name
may be added multiple times to state
.
for each item of var1 times each item of state, this is an O(n*m)
problem or in this case basically O(n²)
as m
is pretty fast catching up to n
. You should find a better approach here.
And I'm almost certain that [var1]
is wrong here as the dependency for useEffect
. But you'd need to show where this value comes from to fix that, too.
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