Question

我具有以下提取功能。如何添加完成块，以便在完成时可以执行某些操作？

此查询将在内部多次运行代码。

func getFollowers() {
    print("get followers called")
    let ref = Database.database().reference()
    ref.child("users2").child((Auth.auth().currentUser?.uid)!).child("Following").observe(.childAdded) { (snap) in
        let personBeignFollow = snap.key
        self.peopleUserFollows.append(personBeignFollow)
        print("Appened: ", personBeignFollow)
        self.fetchAllUserFirstPostMedia(user: personBeignFollow)
    }
}

我看过here，但无法使其正常工作。

这是我尝试过的：

    func getFollowers(_: ()-> ()) {
    print("get followers called")
    let ref = Database.database().reference()
    ref.child("users2").child((Auth.auth().currentUser?.uid)!).child("Following").observe(.childAdded) { (snap) in
        let personBeignFollow = snap.key
        self.peopleUserFollows.append(personBeignFollow)
        print("Appened: ", personBeignFollow)
        self.fetchAllUserFirstPostMedia(user: personBeignFollow)
    }
}

然后将其称为：

getFollowers() {
   self.collectionView.reloadData()
}

Answer 1

在函数声明中，可以添加以下内容：

func getFollowers(_ completion: @escaping () -> Void) {
    print("get followers called")
    let ref = Database.database().reference()
    ref.child("users2").child((Auth.auth().currentUser?.uid)!).child("Following").observe(.childAdded) { (snap) in
        let personBeignFollow = snap.key
        self.peopleUserFollows.append(personBeignFollow)
        print("Appened: ", personBeignFollow)
        self.fetchAllUserFirstPostMedia(user: personBeignFollow)

       // tell the calling function to execute the completion handler again
       completion()
    }
}

然后使用它，您将执行以下操作：

getFollowers {
 // whatever you want to do after the query has run
}

这并不直接重要，但作为一种常见的设计实践，最好将从查询中检索到的新数据作为参数传递给完成处理程序，而不是在类上分配属性。< / p>

这看起来像这样：

func getFollowers(_ completion: (String) -> Void) {
    ref.child("users2").child((Auth.auth().currentUser?.uid)!).child("Following").observe(.childAdded) { (snap) in
        let personBeignFollow = snap.key
        print("Appened: ", personBeignFollow)        
       // tell the calling function to execute the completion handler again
       completion(personBeignFollow)
    }
}

，然后您的呼叫站点可能如下所示：

getFollowers { newUser in
    self.fetchAllUserFirstPostMedia(user: newUser)
}

如何在.childAdded firebase查询中添加完成块？

1 个答案: