ios - 让 AuthListener 等待，直到 for 循环完成

Question

我在每次登录时都会读取用户的数据。由于我在 AppDelegate.swift 中有一个 Firebase AuthListener，因此一旦用户登录， View 就会发生变化。

问题是，在某些情况下， View 的变化速度快于数据的处理速度，这会导致屏幕上没有所需的数据。

过去，我通过在更改 View 的代码中添加: databaseRef.observeSingleEvent(of: .value, with: { snap in ... }) 来绕过此问题:

if user != nil && currentCar == "auto auswählen" {
                databaseRef.observeSingleEvent(of: .value, with: { snap in
                    if user?.isAnonymous == false {
                        let controller = storyboard.instantiateViewController(withIdentifier: "RootPageViewController") as! RootPageViewController
                        let vc = storyboard.instantiateViewController(withIdentifier: "ProfileViewController") as! ProfileViewController
                        vc.readTimeline()
                        self.window?.rootViewController = controller
                        self.window?.makeKeyAndVisible()
                    } else if user?.isAnonymous == true {
                        let controller = storyboard.instantiateViewController(withIdentifier: "RootPageViewController") as! RootPageViewController
                        self.window?.rootViewController = controller
                        self.window?.makeKeyAndVisible()
                    }
})

这工作得很好，但现在我在 for 循环的帮助下读取数据，它不会，因为数据库请求比 for 循环更早完成:

databaseRef.child("users").child(uid).observeSingleEvent(of: .value, with: { (snapshot) in
            let value = snapshot.value as? NSDictionary

            for n in 1...snapshot.childrenCount {
                databaseRef.child("users/\(uid)").child(String(n)).observeSingleEvent(of: .value, with: { (snapshot) in
                    let value = snapshot.value as? NSDictionary

                    ...

                }) { (error) in
                    print(error.localizedDescription)
                }
            }
        }) { (error) in
            print(error.localizedDescription)
        }
    }

如何让 AppDelegate.swift 和 AuthListener 等待 for 循环完成？

Answer 1

您想要等待进入新 View ，直到所有数据加载完毕。一种方法是计算已加载的子节点数量，然后在加载完所有子节点后继续。

代码看起来像这样:

databaseRef.child("users").child(uid).observeSingleEvent(of: .value, with: { (snapshot) in
    let value = snapshot.value as? NSDictionary
    let loadedCount = 0

    for n in 1...snapshot.childrenCount {
        databaseRef.child("users/\(uid)").child(String(n)).observeSingleEvent(of: .value, with: { (snapshot) in
            loadedCount = loadedCount + 1
            let value = snapshot.value as? NSDictionary

            ...

            if (loadedCount == snapshot.childrenCount) {
               // TODO: all data is loaded, move to the next view
            }
        }) { (error) in
            print(error.localizedDescription)
        }
    }
}) { (error) in
    print(error.localizedDescription)
}