React Native-在另一个函数中无法识别该函数

Question

I'm using Firebase Realtime Storage. I'm trying to call function from inside the firebase ref.on() function.

My code:

export default class HomeScreen extends React.Component {

  constructor(props) {
    super(props);

    ref.on("value", function (snapshot) {
      dosomething(snapshot.val()) //<-- not recognized
    }, function (errorObject) {
      console.log("The read failed: " + errorObject.code);
    });
   } 

  dosomething(val){
    //...
  }

  //....
});

I'm trying to make the dosomething() function to get called from the ref.on() function but React don't recognize the dosomething() function

Why is it happened recognize and How do I fix it?

Thanks for your help :)

Answer 1

you'll need to change function (snapshot) { to (snapshot) => {

now the this inside that callback is the this value of the enclosing lexical context - ie the constructor

and then you can use this.dosomething - because dosomething is a property of this

export default class HomeScreen extends React.Component {

  constructor(props) {
    super(props);

    ref.on("value", (snapshot) => {
      this.dosomething(snapshot.val())
    }, function (errorObject) {
      console.log("The read failed: " + errorObject.code);
    });
   } 

  dosomething(val){
    //...
  }

  //....
});