swift - 无返回值

Question

此函数返回空数组有什么原因吗？我已经通过调试器运行它，for 循环正在工作，并将用户附加到 newUsers 数组中，但当它完成并返回值时，它是空的。

func fetchUsers(ref:FIRDatabaseReference) -> [User] {
        var newUsers = [User]()
        ref.observeEventType(.Value, withBlock: {snapshot in
            for user in snapshot.children {
                let users = User(snapshot: user as! FIRDataSnapshot)
                newUsers.append(users)
            }
        })
        print("closure exited. There are \(newUsers.count) Users in newUsers")
        return newUsers
    }

Answer 1

使用完成，因为您处于异步 block 中。试试这个

func fetchUsers(ref:FIRDatabaseReference, completion(users: [Users])) {
    var newUsers = [User]()
    ref.observeEventType(.Value, withBlock: {snapshot in
        for user in snapshot.children {
            let users = User(snapshot: user as! FIRDataSnapshot)
            newUsers.append(users)
        }
        print("closure exited. There are \(newUsers.count) Users in newUsers")
        completion(users: newUsers)
    })

}