Firebase 和 ionic 2，将用户 UID 添加到数据库时出现问题答案

【问题标题】：Firebase and ionic 2, issue when adding user UID to databaseFirebase 和 ionic 2，将用户 UID 添加到数据库时出现问题
【发布时间】：2017-07-30 20:27:09
【问题描述】：

我正在尝试将变量 ownerID 传递到 Firebase 函数之外，但在函数关闭后它会变为 UNDEFINED，即使该变量是在函数外部声明的。我该如何解决这个问题？

addBook():void {
var ownerID
let prompt = this.alertCtrl.create({
  title: 'Adicionar Livros',
  message: 'Adicione as informações do livro',
  inputs: [
    {
      name: 'title',
      placeholder: "Título do Livro"
    },
    {
      name: 'author',
      placeholder: "Nome do Autor"
    },
    {
      name: 'description',
      placeholder: "Descrição do Livro"
    },
    {
      name: 'city',
      placeholder: "Sua Cidade"
    },
  ],
  buttons: [
    {
      text: "Cancelar",
      handler: data => {
        console.log("cancel clicked");
      }
    },
    {
      text: "Salvar",
      handler: data => {
        firebase.auth().onAuthStateChanged(function(user) {
          if (user) {
            ownerID = user.uid;
            console.log(ownerID); // this prints fine
          }
        })
          console.log(ownerID) // this is undefined
        this.books.push({
          title: data.title,
          author: data.author,
          description: data.description,
          city: data.city,
          owner: ownerID
        })
      }
    }
  ],
})
prompt.present();
}

【问题讨论】：

标签： typescript firebase firebase-realtime-database ionic2 firebase-authentication

【解决方案1】：

如果我没记错firebase.auth().onAuthStateChanged 返回一个承诺，所以我认为你需要一个then()

firebase.auth().onAuthStateChanged(user => {
   if (user) {
      ownerID = user.uid;
   }
}).then(data => {
   console.log(ownerID)
});

onAuthStateChanged

返回包含 void 的非 null firebase.Promise

【讨论】：