如何将从Firebase读取的值分配给变量

Question

I am trying to read the value from firebase and assign it to a global variable but it didn't work.

    public points: any;

    readPoints(): any{
        this.userProfile.child(this.user.uid).once('value').then((snapshot) =>{
            this.points = snapshot.val().user_points;
        });
    }
    console.log(this.points); //undefined




 Users{
          SAdS4cW57DSLuWr2obbZYUHsmAL2{
                user_points: 20
.....

Answer 1

好吧，您的变量是this.points但是您正在尝试打印this.point

Answer 2

I read this article from firebase and seem like solution is to call another function instead of assign value directly to variable

public points: any;

readPoints(): any{
    this.userProfile.child(this.user.uid).once('value').then((snapshot) =>{
         this.getPoints(snapshot.val().user_points);
    });

}
getPoints(point: any = null): any{
    this.points = parseInt(point) + 20;
    console.log("point="+ this.points);
}

Answer 3

Your code seems right to me, try printing your snapshot.val() to see what it gives you. I'll just add a code of how i imagine your full database query is.

firebase.database().ref('Users/').child(this.user.uid).once('value').then(snapshot => {
  this.points = snapshot.val().user_points;
})

Does it gives any error on the console? Is it getting the this.user.id right?