使用Firebase，即使正在记录firebase.auth().currentUser，它也是一个空值

问题描述

我在service.TS文件中创建了一个查询，该查询显示了基于登录用户的UID的项状态":

I created a query that is in a service.TS file that shows an items "state" that is based on a logged in user's UID:

getLists(): FirebaseListObservable<any> {

firebase.auth().onAuthStateChanged(function(user) {
  if (user) {console.log("blah", firebase.auth().currentUser.uid)
    // User is signed in.
  }
});
  return this.db.list('/foods', {
    query: {
      orderByChild: 'state/'+firebase.auth().currentUser.uid+'/state',
      equalTo: 'listed'
    }
  });
}

使用此查询，我收到一条错误消息:

Using this query, I'm getting an error that reads:

未捕获(承诺):TypeError:null不是对象(评估' WEBPACK_IMPORTED_MODULE_2_firebase_app "auth" .curren‌tUser.uid').

Uncaught (in promise): TypeError: null is not an object (evaluating 'WEBPACK_IMPORTED_MODULE_2_firebase_app"auth".curren‌​tUser.uid').

使用 {console.log("blah"，firebase.auth().currentUser.uid)正确地在日志中显示UID，确认用户是登录.

Using {console.log("blah", firebase.auth().currentUser.uid), which you can see above, correctly displays the UID in the log, confirming that the user is signed in.

我不确定是否相关，但是页面的主要TS文件通过以下方式调用此查询:

I'm not sure if it's relevant but this query is being called by the page's main TS file with:

    ngOnInit() {

    this.moviesSvc.getLists()
                  .subscribe(lists => {console.log(lists); console.log("UID", firebase.auth().currentUser.uid); this.lists = lists})
  }

我需要怎么做才能正确地将UID传递给查询?

What do I need to do to correctly pass the UID to the query?

推荐答案

onAuthStateChanged()是异步的，因此，当用户在其回调中使用 uid 时，则仅执行如下操作:

onAuthStateChanged() is asynchronous, so when you have the user uid in its callback, then only perform your operation, like this:

getLists(): FirebaseListObservable<any> {

    var self = this;

    firebase.auth().onAuthStateChanged(function(user) {
        if (user) {
            // User is signed in.
            var userID = user.uid;

            return self.db.list('/foods', {
                query: {
                    orderByChild: 'state/' + userID + '/state',
                    equalTo: 'listed'
                }
            });
        }
    });

}

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