如何獲得 react-native 中的 firebase 值？

Question

我想在構造函數發生時讀取 firebase 的值並將其保存在 this.state 中。 我應該怎么辦？

constructor(props) {
    super(props);
    var userId = firebase.auth().currentUser.uid;
    return firebase.database().ref("/users" + userId)
    .once("value").then(function(snapshot) {
      var uid = (snapshot.val() && snapshot.val().uid)
      var nickname = (snapshot.val() && snapshot.val().nickname)
    }),
    this.state = {
      //uid: firebase.auth().currentUser.uid,
      uid: "",
      nickname: "",

    };
  }

Answer 1

對setState的調用需要在回調中：

firebase.database().ref("/users" + userId)
    .once("value").then(function(snapshot) {
      var uid = (snapshot.val() && snapshot.val().uid)
      var nickname = (snapshot.val() && snapshot.val().nickname)

      this.setState({
        uid: uid,
        nickname: nickname,    
      });
    }),