CODEWITHSUNDEEP
firebasereact-nativefirebase-realtime-databaseexpo
quentin mayer
quentin mayer

Reputation: 137

(React native) Can't get data out of the Firebase database method

i trying to get the data from my database, in componentWillMount(), it works fine with this :

  var userData = null
firebase.database().ref('/users/' + user.uid).once('value').then(function(snapshot) {
        userData = snapshot.val()
        console.log(userData)
      });

But it only works in the method only, i tried to asign the value to a variable but i can't get it outside even with this.setstate. I am really lost it looks easy but i don't know how ... Thanks for help.

Upvotes: 0

Views: 1386

Answers (2)

Jaydeep Galani
Jaydeep Galani

Reputation: 4961

Well, what's happening here is,

your firebase method is taking a time to get data and because everything is asynchronous here, javascript will not wait until your firebase method is executed.

Immediate next line of firebase.database().... will be executed before this completes.

So you might need to set your data into state using setState or you can use a class variable instead of a local variable.

do this,

constructor(props){
   super(props);
   this.state={
     data:null //either do this
   }
   this.localData=null; // or this
}


firebase.database().ref('/users/' + user.uid).once('value').then(function(snapshot) {
        this.setState({data:snapshot.val()});
        this.localData = snapshot.val();
        console.log(this.localData)
});

Upvotes: 0

Doug Stevenson
Doug Stevenson

Reputation: 317372

once() is asynchronous and returns immediately with a promise. The promise does not block your code when you attach a then callback to it. userData won't be populated in the callback from the promise until after the database query completes, and you have no guarantee when that will be. If your code tries to access userData before it's finally populated, it will still have its original null value.

Upvotes: 1

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