Javascript firebase在一个位置返回未定义的用户id，在另一个位置返回正确的值

我使用以下函数获取用户id：

currentUser.js

import firebase from './firebase';

export default function getCurrentUserID() {
  var user = firebase.auth().currentUser;
  var uid; 
  if (user != null) {
    uid = user.uid;  // The user's ID, unique to the Firebase project. Do NOT use
    // this value to authenticate with your backend server, if
    // you have one. Use User.getToken() instead.
    return uid;
  }
  return uid;
}

import getCurrentUserID from './currentUserID';
import getFirestoreDB from './firestoreDB';
import Project from './project';
const addProjectBtn = document.getElementById('addProjectBtn');
function addProject() {
    const title = prompt('Insert title');
    const description = prompt('Insert Description');
    const project = new Project(title, description);
    const db = getFirestoreDB();
    const currentUserUID = getCurrentUserID();
    alert(currentUserUID); 
    db.doc(`users/${currentUserUID}/projects/${title}`).set({ ...project }).then(() => {
        alert("Success");
    }).catch((error) => {
        alert("Error " + error);
    });
}

export default function enableAddProjectBtnFunctionality() {
    addProjectBtn.addEventListener('click', addProject);
}

import getCurrentUserID from "./currentUserID";
import getFirestoreDB from './firestoreDB';

var db = getFirestoreDB(); 

export default function displayProjects(){
    var uid = getCurrentUserID(); 
    if(uid){
        alert(uid); 
        var projectsRef = db.collection("users").doc(`${uid}`).collection("projects"); 
        projectsRef.get().then((querySnapshot) => {           
                querySnapshot.forEach((doc) => {
                    // doc.data() is never undefined for query doc snapshots
                    console.log(doc.id, " => ", doc.data());
                });
            });  
    }
          
}

以下代码可以使用按钮添加项目，效果良好：

addProject.js

import firebase from './firebase';

export default function getCurrentUserID() {
  var user = firebase.auth().currentUser;
  var uid; 
  if (user != null) {
    uid = user.uid;  // The user's ID, unique to the Firebase project. Do NOT use
    // this value to authenticate with your backend server, if
    // you have one. Use User.getToken() instead.
    return uid;
  }
  return uid;
}

import getCurrentUserID from './currentUserID';
import getFirestoreDB from './firestoreDB';
import Project from './project';
const addProjectBtn = document.getElementById('addProjectBtn');
function addProject() {
    const title = prompt('Insert title');
    const description = prompt('Insert Description');
    const project = new Project(title, description);
    const db = getFirestoreDB();
    const currentUserUID = getCurrentUserID();
    alert(currentUserUID); 
    db.doc(`users/${currentUserUID}/projects/${title}`).set({ ...project }).then(() => {
        alert("Success");
    }).catch((error) => {
        alert("Error " + error);
    });
}

export default function enableAddProjectBtnFunctionality() {
    addProjectBtn.addEventListener('click', addProject);
}

import getCurrentUserID from "./currentUserID";
import getFirestoreDB from './firestoreDB';

var db = getFirestoreDB(); 

export default function displayProjects(){
    var uid = getCurrentUserID(); 
    if(uid){
        alert(uid); 
        var projectsRef = db.collection("users").doc(`${uid}`).collection("projects"); 
        projectsRef.get().then((querySnapshot) => {           
                querySnapshot.forEach((doc) => {
                    // doc.data() is never undefined for query doc snapshots
                    console.log(doc.id, " => ", doc.data());
                });
            });  
    }
          
}

但是，下面显示项目的代码不起作用。警报（uid）在此显示未定义，但上面显示了正确的用户id

displayProjects.js

import firebase from './firebase';

export default function getCurrentUserID() {
  var user = firebase.auth().currentUser;
  var uid; 
  if (user != null) {
    uid = user.uid;  // The user's ID, unique to the Firebase project. Do NOT use
    // this value to authenticate with your backend server, if
    // you have one. Use User.getToken() instead.
    return uid;
  }
  return uid;
}

import getCurrentUserID from './currentUserID';
import getFirestoreDB from './firestoreDB';
import Project from './project';
const addProjectBtn = document.getElementById('addProjectBtn');
function addProject() {
    const title = prompt('Insert title');
    const description = prompt('Insert Description');
    const project = new Project(title, description);
    const db = getFirestoreDB();
    const currentUserUID = getCurrentUserID();
    alert(currentUserUID); 
    db.doc(`users/${currentUserUID}/projects/${title}`).set({ ...project }).then(() => {
        alert("Success");
    }).catch((error) => {
        alert("Error " + error);
    });
}

export default function enableAddProjectBtnFunctionality() {
    addProjectBtn.addEventListener('click', addProject);
}

import getCurrentUserID from "./currentUserID";
import getFirestoreDB from './firestoreDB';

var db = getFirestoreDB(); 

export default function displayProjects(){
    var uid = getCurrentUserID(); 
    if(uid){
        alert(uid); 
        var projectsRef = db.collection("users").doc(`${uid}`).collection("projects"); 
        projectsRef.get().then((querySnapshot) => {           
                querySnapshot.forEach((doc) => {
                    // doc.data() is never undefined for query doc snapshots
                    console.log(doc.id, " => ", doc.data());
                });
            });  
    }
          
}

---

有人能帮我找出问题所在以及如何解决吗？

很可能是在用户登录完成之前执行了

displayProjects

方法

在这种情况下，获取用户状态的正确方法是使用身份验证状态侦听器，如上的文档中的第一个代码片段所示

在您的代码中，如下所示：

export default function displayProjects(){
  firebase.auth().onAuthStateChanged(function(user) {
    if (user) {
      var uid = user.uid;
      var projectsRef = db.collection("users").doc(`${uid}`).collection("projects"); 
      projectsRef.get().then((querySnapshot) => {           
        querySnapshot.forEach((doc) => {
          console.log(doc.id, " => ", doc.data());
        });
      });  
    }
  });
}

---

我刚刚阅读了一个与此类似的问题，因为我当前遇到了一个问题。currentUser:-这是否相关？它描述了相同的行为，解决方案与我在回答中显示的相同：使用身份验证状态侦听器。一旦您尝试了我的答案中的方法，请告诉我。啊，我正在测试。currentUser作为已加载的组件，但onAuthStateChanged没有跟上。似乎.currentUser可能有点不一致。我将实现上述功能。谢谢。这不是太不一致，因为恢复用户的身份验证状态需要一些时间。访问

currentUser

是一个同步操作，这意味着它可能在设置

currentUser

之前发生。使用身份验证状态侦听器可以避免该问题。如果我的答案有用，请单击向上投票按钮(▲) 如果它回答了您的问题，请单击复选标记(✓) 接受它。这样其他人知道你得到了（足够）的帮助。另外，我只调用了一次displayProjects（），那么它如何跟踪AuthState的更改？嘿，M代码。你有什么进展吗？你有没有机会阅读下面的我的答案并在代码中尝试它？如果我的答案有用，请单击“向上投票”按钮(▲) 如果它回答了您的问题，请单击复选标记(✓) 接受它。这样别人就会知道你已经得到了（足够的）帮助。也请参见