Question

我有一个Chat ViewController和一个ChatList

每当我点击聊天列表上的对话时，我会计算所有孩子的总数并保存聊天大小（消息数量）。

然而，似乎观察者函数被调用了两次并且弄乱了我真实的聊天大小。

let messagesChannelRef = mainChannelRef.child(channelid).child("messages")
messagesChannelRef.observe(FIRDataEventType.value, with: { (snapshot: FIRDataSnapshot) -> Void in

   UserDefaults.standard.set(snapshot.childrenCount, forKey: "latestreadchatsize@\(channelid)")
   UserDefaults.standard.synchronize()

})

如何避免两次调用的观察函数？

更新的问题：

以下是我使用的代码..

class ChannelListTableViewController: UITableViewController {
...........
...........

private lazy var channelRef: FIRDatabaseReference = FIRDatabase.database().reference().child("channels")

..........

func showChatDialog(channelObj: Channel){
        let navChatVc: UINavigationController = self.storyboard?.instantiateViewController(withIdentifier: "navChatView") as! UINavigationController
        let chatVc : ChatViewController = navChatVc.viewControllers.first as! ChatViewController
        chatVc.senderDisplayName = senderDisplayName
        chatVc.channel = channelObj
        chatVc.channelRef = channelRef.child(channelObj.id)

        let channelid = channelObj.id
        let messagesChannelRef = channelRef.child(channelid).child("messages")

        self.present(navChatVc, animated:true, completion: { () -> Void in

        let channelid = channelObj.id
            channelRef.child(channelid).child("messages").observe(FIRDataEventType.value, with: { (snapshot: FIRDataSnapshot) -> Void in

                UserDefaults.standard.set(snapshot.childrenCount, forKey: "latestreadchatsize@\(channelid)")
                UserDefaults.standard.synchronize()

            })
        })
}

...........
...........

} //end of class

每当点击showChatDialog时，它实际上只调用一次但是当我从另一个客户端发送聊天消息时，则会调用observe函数两次？

我知道聊天客户端互相调用新消息。因此，当使用新消息更新Firebase时，我想它会重新调用observe函数，这意味着它会监听任何更新？

Answer 1

解决方案更新

最后，用2种可能的方式找到答案

ObserveSingleType
或删除FIRDatabaseHandle观察员

//检查单个频道的总邮件大小

//you can choose one of these 2 ways
let mainChannelRef: FIRDatabaseReference = FIRDatabase.database().reference().child("channels")

//1st way
if let channelid = channel?.id {
    mainChannelRef.child(channelid).child("messages").observeSingleEvent(of: .value, with: { (snapshot) in
        UserDefaults.standard.set(snapshot.childrenCount, forKey: "latestreadchatsize@\(channelid)")
        UserDefaults.standard.synchronize()
    })
}


//2nd way
if let channelid = channel?.id {
    let newRefHandle: FIRDatabaseHandle  = mainChannelRef.child(channelid).child("messages").observe(FIRDataEventType.value, with: { ( snapshot: FIRDataSnapshot) -> Void in
            UserDefaults.standard.set(snapshot.childrenCount, forKey: "latestreadchatsize@\(channelid)")
            UserDefaults.standard.synchronize()
    })
    mainChannelRef.child(channelid).child("messages").removeObserver(withHandle: newRefHandle)
}

它们都确保只点击观察者一次

Firebase观察被叫两次？

1 个答案: