轉換觀察到在Firebase中觀察SingleSvent時出錯

Question

我現在有一個觀察手柄，用於檢查何時添加新通道。我希望它是一個帶有按鈕的observeSingleEvent，當用戶點擊它時將重新加載頻道。 observeSingleEvent正常工作。這是代碼：

private func observeChannels() { 
    channelRefHandle = channelRef.observe(.childAdded, with: { (snapshot) -> Void in 
     self.playersInChannnel.append("\(snapshot.childrenCount)") 
     let channelData = snapshot.value as! Dictionary<String, AnyObject> 
     let id = snapshot.key 
     if let name = channelData["name"] as! String!, name.characters.count > 0 { 
      self.channels.append(Channel(id: id, name: name)) 
      self.tableView.reloadData() 
     } else { 
      print("Error! Could not decode channel data") 
     } 
    }) 
} 

我現在試圖將其轉換爲observeSingleEvent，把打印的說法錯誤，無法解碼通道數據。這是我的代碼：

func reloadChannels() 
{ 
    channelRef.observeSingleEvent(of: .value, with: { (snapshot) -> Void in 
     self.playersInChannnel.append("\(snapshot.childrenCount)") 
     let channelData = snapshot.value as! Dictionary<String, AnyObject> 
     let id = snapshot.key 
     if let name = channelData["name"] as! String!, name.characters.count > 0 { 
      self.channels.append(Channel(id: id, name: name)) 
      self.tableView.reloadData() 
     } else { 
      print("Error! Could not decode channel data") 
     } 
    }) 
} 

這段代碼有什麼問題？這是快照的從observeSingleEvent打印：

Snap (channels) { 
    "-Ke3g8tLH9A-_iTVjQhq" =  { 
     "-Ke3g8tO2XPCbyIjP4Op" =   { 
      PictureVersion = ""; 
      userID = keVlTMUXyRViUsTVjTnKdvZs7mg1; 
      username = pietje; 
     }; 
     name = test; 
    }; 
    "-Ke3gFbijlcQGuJXe42L" =  { 
     "-Ke3gFbjsEgpA3wjM1Jv" =   { 
      PictureVersion = ""; 
      userID = keVlTMUXyRViUsTVjTnKdvZs7mg1; 
      username = pietje; 
     }; 
     name = test2; 
    }; 
} 
Error! Could not decode channel data 

同樣，燒成observeChannels（）是表示沒有錯誤。謝謝。

Answer 1

您不只是從observe更改爲observeSingleEvent，您也從觀察.childAdded切換到觀察.value。由於您現在正在偵聽.value，這意味着您一次獲得的快照包含全部子節點（即使只有一個匹配的子節點）。

出於這個原因，你將需要循環快照的孩子們，讓你不得不信道數據之前：

func reloadChannels() 
{ 
    channelRef.observeSingleEvent(of: .value, with: { (snapshot) -> Void in 
     self.playersInChannnel.append("\(snapshot.childrenCount)") 
     for channelSnap in snapshot.children { 
      let channelData = (channelSnap as! FIRDataSnapshot).value as! Dictionary<String, AnyObject> 
      let id = (channelSnap as! FIRDataSnapshot).key 

      if let name = channelData["name"] as! String!, name.characters.count > 0 { 
       self.channels.append(Channel(id: id, name: name)) 
       self.tableView.reloadData() 
      } else { 
       print("Error! Could not decode channel data") 
      } 
     } 
    }) 
} 

看到這個問題的答案以獲得更多關於如何循環的兒童快照：Iterate over snapshot children in Swift (Firebase)