ios - 为数组中的每个字符串获取 firebase 数据

Question

在我的 Firebase 实时数据库中，我有一个标记为“组”的节点，这就是我构建它的方式:

在上面的“用户”下面，我试图使用这些用户 ID 来引用每个用户中的数据。这就是我构建我试图引用的每个“用户”节点的方式:

在下面的代码片段中，我从组的用户子节点的快照中获取 userId。然后我在这些 userId 上运行 for-in 循环以访问“用户”节点中的信息。

print("This should be the individual userId: ", userId) 语句正确打印出每个 userId。 userRef.observeSingleEvent(of: .value, with: { (snapshot) in 在第一次调用 for-in 循环时被调用，但它几乎就像被忽略了一样。应用程序崩溃是因为user array comes up empty at the end. 然而，数组中出现了大量空用户(当查看调试区域中的 Variables View 时)。所以，我觉得我正在运行某种形式的冗余循环什么的。

guard let groupChatPartnerId = message.chatPartnerId() else {
    return
}

var users: [User]?

let ref = Database.database().reference().child("groups").child(groupChatPartnerId)
ref.observeSingleEvent(of: .value, with: { (snapshot) in

    let groupId = snapshot.key

    let groupName = snapshot.childSnapshot(forPath: "groupName").value as! String

    let userIdDictionary = snapshot.childSnapshot(forPath: "users").value as! Dictionary<String,AnyObject>
    let userIds = Array(userIdDictionary.keys)
    print("userIds: ", userIds)



    for userId in userIds {
        print("This should be the individual userId: ", userId)
        let userRef = Database.database().reference().child("users").child(userId)
        userRef.observeSingleEvent(of: .value, with: { (snapshot) in
            print("This is the snapshot: ", snapshot)
            let email: String = snapshot.childSnapshot(forPath: "email").value as! String
            print("user's email: ", email)
            let uid = snapshot.key
            let username = snapshot.childSnapshot(forPath: "username").value as! String
            let profileImageUrl = snapshot.childSnapshot(forPath: "profileImageUrl").value as! String

            let user = User(uid: uid, userUsername: username, userProfileImageUrl: profileImageUrl, userEmail: email)

            users?.append(user)
            print("user to append to users: ", user)

        }, withCancel: nil)

    }

    print("users :", users)

    let group = Group(groupId: groupId, groupName: groupName, users: users!)
    self.showChatControllerForGroup(group: group)

}, withCancel: nil)

如果您需要任何其他信息，请告诉我。提前致谢!

Answer 1

所有数据都是从 Firebase 异步加载的 当您打印 users 时，userRef.observeSingleEvent 还没有完成。因此，打印所有用户的代码必须位于 userRef.observeSingleEvent 的完成句柄内，并且必须仅在加载所有用户后运行。

一个简单的方法是比较 users 的长度和 userIds 的长度。如果它们相同，则您已加载所有用户:

for userId in userIds {
    print("This should be the individual userId: ", userId)
    let userRef = Database.database().reference().child("users").child(userId)
    userRef.observeSingleEvent(of: .value, with: { (snapshot) in
        print("This is the snapshot: ", snapshot)
        let email: String = snapshot.childSnapshot(forPath: "email").value as! String
        print("user's email: ", email)
        let uid = snapshot.key
        let username = snapshot.childSnapshot(forPath: "username").value as! String
        let profileImageUrl = snapshot.childSnapshot(forPath: "profileImageUrl").value as! String

        let user = User(uid: uid, userUsername: username, userProfileImageUrl: profileImageUrl, userEmail: email)

        users?.append(user)
        print("user to append to users: ", user)

        if userIds.count == users.count {
            print("users :", users)
        }
    }, withCancel: nil)

}