React Native - AsyncStorage returns me null if I try to get the string

Question

I'm working with AsyncStorage, I need to get the value stored into "facoltà" and save it into "promessa" calling this.setState. I wrote that code:

constructor(props){
  super(props)
  AsyncStorage.setItem("facoltà","PROFS.json")
}
componentWillMount(){
  AsyncStorage.getItem("facoltà").then((value)=>
  { 
    console.log(value); // the console returns me PROFS.json so I thought it was working
    this.setState({promessa:value})
  }):
  var dataObjects=require("../JsonLists/"+this.state.promessa) // but here this.state.promessa returns me null
 }

the problem is that this.state.promessa returns me "null" instead of "PROFS.json" and I can't figure out how to solve it. Thanks in advance for your answers.

You won't be able to import your file with this way : `require("../JsonLists/"+this.state.promessa)`. You can not dynamically import files. Take a look at [this answer](https://stackoverflow.com/a/43517912/5555458) to understand why. — Antoine Grandchamp, Jul 21 '17 at 18:24
Thank you, I fixed the require error that I made as Antoine Grandchamp said. Then I fixed the dataObject issue placing it into the then chain as you said, thank you. — Matteo Veraldi, Jul 23 '17 at 19:59

score 2 · Answer 1 · answered Mar 05 '18 at 10:06

ComponentWillMount will not finish the getItem Promise after the setItem Promise in the constructor.

try :

componentWillMount(){
 AsyncStorage.setItem("facoltà",PROFS.json)
}

render(){
...
  AsyncStorage.getItem("facoltà").then((value)=>alert(value));
...
}

this should alert your data.

score 0 · Answer 2 · answered Jul 21 '17 at 18:17

AsyncStorage.getItem returns a promise, thus will be resolved in the callback with then. That means your next line var dataObjects=require("../JsonLists/"+this.state.promessa) is executed before the promise is resolved.

You should put the line within the then callback and have a default initial value if you need dataObjects immediately in your componentWillMount method.

score 0 · Answer 3 · answered Jul 21 '17 at 18:17

0

I think it's a timing issue. You're using a promise with .then, which is setting the state after var dataObjects is trying to require it.

Have you tried placing the var dataObjects inside your .then code?

answered Jul 21 '17 at 18:17

stevenlacerda

1,187
2
9
21

score 0 · Answer 4 · answered Mar 05 '18 at 10:48

0

async myMethode() {
AsyncStorage.getItem("").then((value)=>alert(value));

}

try like this.Call methode where it required

answered Mar 05 '18 at 10:48

Manikanta Adimulam

25
3

async keyword will help you get data in asynchronously – Manikanta Adimulam Mar 05 '18 at 10:50

score 0 · Answer 5 · answered Jun 15 '19 at 23:06

Using Async/Await.

async componentDidMount () {


    try {

        const item = await this.someMethodAsync();

    } catch (e) {

       console.log("Error getting item", e);
    }
}    

async someMethodAsync () {
     try {

          let item = AsyncStorage.getItem("foo");
          console.log(item);
     catch (e) {
          throw e;
     }

     return item; // Could be any value, including null.
}

React Native - AsyncStorage returns me null if I try to get the string

5 Answers5