我尝试在componentDidmount的for循环中使用setState更新状态，但是每次出现此错误“无法读取null的'setState'属性”

import React,{Component} from 'react';
import '../../../Config'
import * as firebase from  'firebase';
import './Header.scss'
class MessageBox extends Component {
  constructor(props){
    super(props);
    this.state = {

      users:[],}
    this.setState= this.setState.bind(this)
  }
  componentDidmount(){

   firebase.database()
    .ref("Users")
    .on('value',gotData,errData);
    function gotData (data) {
      var users = data.val();
      console.log(users,"uuuuuuuuuuuu")
      var keys=Object.keys(users);
      console.log(keys,"keys")
      for (var i = 0; i<keys.length; i++){
        var k = keys[i];
        var myuser = (users[k]);
           this.setState({users: myuser});
        console.log(myuser,'newUser')
        console.log(myuser.username,"myusername")
        console.log(myuser.id,"myuserId")
        console.log(myuser.imageURL,"myuserImage")