javascript - 直接从 firebase rtdb 获取数据时出现 TypeError : Cannot read property 'setState' of null,

Question

为什么我的状态没有使用我直接从 direbase 获取的数据进行更新

我在控制台中获取数据的位置

我在这里做错了什么， 错误在这里

Answer 1

更改此:

const db = firebase.database().ref('users/trainers/'+uid).on('value', function(snapshot){
   // here this refers to the firebase callback scope 
    this.setState({
        .........
        .........
    })
}))

进入此:

const db = firebase.database().ref('users/trainers/'+uid).on('value', (snapshot) =>{
   // here this refers to the firebase callback scope 
    this.setState({
        .........
        .........
    })
}))

使用箭头函数:

An arrow function does not have its own this. The this value of the enclosing lexical scope is used; arrow functions follow the normal variable lookup rules. So while searching for this which is not present in current scope, an arrow function ends up finding the this from its enclosing scope.