Question

我在componentDidMount中调用Firebase之后尝试设置setState：

class Profile extends Component {

constructor(props) {
    super(props)
    this.state = {
        nick: this.props.match.params.user,
        nickid: this.props.match.params.id,
        nickuid: null
    }
}

componentDidMount() {

    firebase.database().ref('/users/').orderByChild('user').equalTo(this.props.match.params.user).once('value').then(function(snapshot) {
      var uid = Object.keys(snapshot.val())[0];
      this.setState({ nickuid: uid }); // error (uid is not null)
      console.log(uid);
    });

}

我有Unhandled Rejection (TypeError): Cannot read property 'setState' of undefined个想法，为什么？

Answer 1

在此处使用箭头功能。通过O(log(n)时，您失去了上下文试试：

function

Answer 2

使用箭头功能。

for list in a:
    for sublist in list:
        for item in sublist:    
            if item == "0" or item == "1":
                item == int(item)

反应：未捕获（承诺）TypeError：无法读取未定义的属性“ setState”

2 个答案: