从 firebase 检索数据失败

Question

由于某种原因，我从 firebase 检索数据后，数据确实检索成功。

    func retrieveData(user: User) {
        //let userID = Auth.auth().currentUser?.uid
        let email = user.emailAddress!
        // print(email)
        databaseRef?.child("userTable").child(email).observe(.value, with: { (snapshot) in
            // Get user value
            print("whats up ")
            if let value = snapshot.value as? [String:String] {
                let res = value["posts"]
                user.deserialize(data: res!)
                if( user === self.u1) {
                    print("they are same obj") // this will print, so they are pointing to the same address
                }
                print(self.u1.posts) // this also printed the things I want
            }
            // ...
        })
        if( user === self.u1) {
            print("they are same obj outside") // this also prints
        }
        print(self.u1.posts) // but once they exist closure, this one just become empty, as as user.posts
    }

我真的不明白这里发生了什么。似乎数据只是在关闭后正确存储。另外，我不知道为什么闭包外的代码首先打印。非常感谢您的帮助！

这是运行结果

它们在外面是相同的 obj [：]

怎么了 他们是同一个obj ["a@hotmail 0": RadiUs.Post]

Answer 1

由于异步操作，您的第三条打印语句（还）没有任何价值。

您的前两个打印语句实际上在您的第三个打印语句之后执行，即使它看起来不像。如果您在每个打印语句处创建断点，您将能够看到执行顺序。

所以为了保证数据是从 Firebase 传回来的，你应该只在这里调用里面的数据：

databaseRef?.child("userTable").child(email).observe(.value, with: { (snapshot) in
        // Manipulate data here
        }

如果您希望调用是同步的，您可以执行以下操作：

    func retrieveData(user: User) {
    //let userID = Auth.auth().currentUser?.uid
    let email = user.emailAddress!
    // print(email)
    databaseRef?.child("userTable").child(email).observe(.value, with: { (snapshot) in
        // Get user value
        print("whats up ")
        if let value = snapshot.value as? [String:String] {
            let res = value["posts"]
            user.deserialize(data: res!)
            if( user === self.u1) {
                print("they are same obj") // this will print, so they are pointing to the same address
            }
            print(self.u1.posts) // this also printed the things I want
        }
        // ...
    })
    if( user === self.u1) {
        print("they are same obj outside") // this also prints
    }
    DispatchQueue.main.async{
        print(self.u1.posts) // Now called sequentially 
    }
}