Question

我正在创建一个简单的聊天应用来学习Swift和Firebase。我有一个查询，检查聊天室的消息加载到tableView中。查询返回快照，但我无法正确存储和加载数据。我从快照创建了一个字典，所以我可以获得单个子值，但它们返回nil：

query.observeSingleEvent(of: .childAdded, with: { snapshot in

            print(snapshot)

            let indexPaths = self.messages.enumerated().map {
                IndexPath(row: $0.0, section: 0)
            }

            guard let messagesDict = snapshot.value as? [String:AnyObject] else { return }
            guard let sender = messagesDict["sender"] as? String else { return }
            guard let text = messagesDict["text"] as? String else { return }
            guard let timestamp = messagesDict["timestamp"] as? Int else { return }

            let message = Message.init(key: snapshot.key, sender: sender as! String, text: text as! String, timestamp: timestamp)

            self.messages.append(message)

            self.tableView.reloadData()
        })

po messagesDict在断点处返回数据：

▿ 1 element
  ▿ 0 : 2 elements
    - key : "-KotqLUUucaRagTRt967"
    ▿ value : 3 elements
      ▿ 0 : 2 elements
        - key : sender
        - value : eGTYRSo81JefgasYLRHUFHUTnEC3
      ▿ 1 : 2 elements
        - key : text
        - value : test
      ▿ 2 : 2 elements
        - key : timestamp
        - value : 1499914135546

应用程序进入我设置guard let sender的下一个断点，但应用程序返回并停止执行代码块的其余部分。如何正确访问发件人，文本和时间戳元素，以便将它们设置为变量并将其存储在表格的数组中？

非常感谢任何帮助。我已经坚持了一段时间，我可以用另一双眼睛！

谢谢！

其他信息：

查询：

let query = rootRef.child("chat-messages/\(chatKey)")

数据库结构：

{
  "chat-messages" : {
    "-KotqKI4zF9cS5XMR9WU" : {
      "-KotqLUUucaRagTRt967" : {
        "sender" : "eGTYRSo81JefgasYLRHUFHUTnEC3",
        "text" : "test",
        "timestamp" : 1499914135546
      }
    },
    "-KotqvBoFFzOTY6Q1fO7" : {
      "-KotqwGAJ85NuAp-Lh3Z" : {
        "sender" : "eGTYRSo81JefgasYLRHUFHUTnEC3",
        "text" : "test",
        "timestamp" : 1499914290279
      }
    },
    "-KotsNgF0ou5MIDn2l5K" : {
      "-KotsOSXw7OS_3xuXZgP" : {
        "sender" : "eGTYRSo81JefgasYLRHUFHUTnEC3",
        "text" : "test",
        "timestamp" : 1499914671997
      },
      "-KotsPqrCpipMLulNNFl" : {
        "sender" : "eGTYRSo81JefgasYLRHUFHUTnEC3",
        "text" : "test44",
        "timestamp" : 1499914677715
      }
    },
    "-Kotsv1Vv19dEF2q7XQu" : {
      "-KotsvYO9JvLY8gdTnA0" : {
        "sender" : "eGTYRSo81JefgasYLRHUFHUTnEC3",
        "text" : "test",
        "timestamp" : 1499914811675
      },
      "-KotsvxKXzIwbyvbwLPp" : {
        "sender" : "eGTYRSo81JefgasYLRHUFHUTnEC3",
        "text" : "test",
        "timestamp" : 1499914813335
      },
      "-Kotsw9vLiEf6KquU__e" : {
        "sender" : "eGTYRSo81JefgasYLRHUFHUTnEC3",
        "text" : "test",
        "timestamp" : 1499914814205
      },
      "-KotswHnzmfkEXih1O7y" : {
        "sender" : "eGTYRSo81JefgasYLRHUFHUTnEC3",
        "text" : "test",
        "timestamp" : 1499914814709
      },
      "-KotszHKBt254jZnUMAl" : {
        "sender" : "eGTYRSo81JefgasYLRHUFHUTnEC3",
        "text" : "test46456",
        "timestamp" : 1499914826967
      }
    },
    "-KoyheS01YxWExSNxl_H" : {
      "-Koyhf3G-FPEDrxQOcpU" : {
        "sender" : "eGTYRSo81JefgasYLRHUFHUTnEC3",
        "text" : "test",
        "timestamp" : 1499995746607
      }
    },
    "-Koyjc_aBaF1kFE-8Bll" : {
      "-Koyjd9PnO6sPOhS7P27" : {
        "sender" : "eGTYRSo81JefgasYLRHUFHUTnEC3",
        "text" : "test",
        "timestamp" : 1499996263096
      },
      "-KoyjdzSEi5twTVQMGOu" : {
        "sender" : "eGTYRSo81JefgasYLRHUFHUTnEC3",
        "text" : "test",
        "timestamp" : 1499996266491
      },
      "-Koyje2C9E524kV7nhLY" : {
        "sender" : "eGTYRSo81JefgasYLRHUFHUTnEC3",
        "text" : "test",
        "timestamp" : 1499996266730
      }
    },
    "-KpfUGw45F1FU2IrR87A" : {
      "sender" : "eGTYRSo81JefgasYLRHUFHUTnEC3",
      "text" : "test",
      "timestamp" : 1500746948396
    },
    "-KpfUHQGuTDi4yZutS5K" : {
      "sender" : "eGTYRSo81JefgasYLRHUFHUTnEC3",
      "text" : "test",
      "timestamp" : 1500746950368
    },
    "-KpfUHdSXeTzauATsDAP" : {
      "sender" : "eGTYRSo81JefgasYLRHUFHUTnEC3",
      "text" : "test",
      "timestamp" : 1500746951277
    },
    "-Kpfia0fXsoqpRtIr1kU" : {
      "sender" : "eGTYRSo81JefgasYLRHUFHUTnEC3",
      "text" : "gerg",
      "timestamp" : 1500750962815
    }
  },
  "chat-participants" : {
    "-KotqKI4zF9cS5XMR9WU" : {
      "eGTYRSo81JefgasYLRHUFHUTnEC3" : {
        "username" : "tester"
      }
    },
    "-KotqvBoFFzOTY6Q1fO7" : {
      "eGTYRSo81JefgasYLRHUFHUTnEC3" : {
        "username" : "tester"
      }
    },
    "-KotsNgF0ou5MIDn2l5K" : {
      "eGTYRSo81JefgasYLRHUFHUTnEC3" : {
        "username" : "tester"
      }
    },
    "-Kotsv1Vv19dEF2q7XQu" : {
      "eGTYRSo81JefgasYLRHUFHUTnEC3" : {
        "username" : "tester"
      }
    },
    "-KoyheS01YxWExSNxl_H" : {
      "eGTYRSo81JefgasYLRHUFHUTnEC3" : {
        "username" : "tester"
      }
    },
    "-Koyjc_aBaF1kFE-8Bll" : {
      "eGTYRSo81JefgasYLRHUFHUTnEC3" : {
        "username" : "tester"
      }
    },
    "-KpfLBjQdPiX2kSrl1yF" : {
      "eGTYRSo81JefgasYLRHUFHUTnEC3" : {
        "username" : "tester"
      }
    }
  },
  "chats" : {
    "-KotqKI4zF9cS5XMR9WU" : {
      "currentName" : "test",
      "date" : 1499914130657
    },
    "-KotqvBoFFzOTY6Q1fO7" : {
      "currentName" : "test",
      "date" : 1499914285904
    },
    "-KotsNgF0ou5MIDn2l5K" : {
      "currentName" : "test",
      "date" : 1499914668844
    },
    "-Kotsv1Vv19dEF2q7XQu" : {
      "currentName" : "test",
      "date" : 1499914809570
    },
    "-KoyheS01YxWExSNxl_H" : {
      "currentName" : "test",
      "date" : 1499995744095
    },
    "-Koyjc_aBaF1kFE-8Bll" : {
      "currentName" : "test",
      "date" : 1499996260740
    },
    "-KpfLBjQdPiX2kSrl1yF" : {
      "currentName" : "test3222",
      "date" : 1500744567786
    }
  },
  "user-chats" : {
    "eGTYRSo81JefgasYLRHUFHUTnEC3" : {
      "-KotqKI4zF9cS5XMR9WU" : {
        "chatKey" : "-KotqKI4zF9cS5XMR9WU",
        "currentName" : "test"
      },
      "-KotqvBoFFzOTY6Q1fO7" : {
        "chatKey" : "-KotqvBoFFzOTY6Q1fO7",
        "currentName" : "test"
      },
      "-KotsNgF0ou5MIDn2l5K" : {
        "chatKey" : "-KotsNgF0ou5MIDn2l5K",
        "currentName" : "test"
      },
      "-Kotsv1Vv19dEF2q7XQu" : {
        "chatKey" : "-Kotsv1Vv19dEF2q7XQu",
        "currentName" : "test"
      },
      "-KoyheS01YxWExSNxl_H" : {
        "chatKey" : "-KoyheS01YxWExSNxl_H",
        "currentName" : "test"
      },
      "-Koyjc_aBaF1kFE-8Bll" : {
        "chatKey" : "-Koyjc_aBaF1kFE-8Bll",
        "currentName" : "test"
      },
      "-KpfLBjQdPiX2kSrl1yF" : {
        "chatKey" : "-KpfLBjQdPiX2kSrl1yF",
        "currentName" : "test3222"
      }
    }
  },
  "user-friends" : {
    "36HDn5XyxjMCcMluJJ9KPBOCDMm1" : {
      "eGTYRSo81JefgasYLRHUFHUTnEC3" : {
        "username" : "tester"
      }
    },
    "eGTYRSo81JefgasYLRHUFHUTnEC3" : {
      "36HDn5XyxjMCcMluJJ9KPBOCDMm1" : {
        "username" : "tester2"
      }
    }
  },
  "user-invites" : {
    "eGTYRSo81JefgasYLRHUFHUTnEC3" : {
      "36HDn5XyxjMCcMluJJ9KPBOCDMm1" : {
        "username" : "tester2"
      }
    }
  },
  "users" : {
    "36HDn5XyxjMCcMluJJ9KPBOCDMm1" : {
      "email" : "tester2@test.com",
      "username" : "tester2"
    },
    "eGTYRSo81JefgasYLRHUFHUTnEC3" : {
      "email" : "test@test.com",
      "username" : "tester"
    }
  }
}

Answer 1

你的字典看起来像：

▿ 1 element
  ▿ 0 : 2 elements
    - key : "-KotqLUUucaRagTRt967"
    ▿ value : 3 elements
      ▿ 0 : 2 elements
        - key : sender
        - value : eGTYRSo81JefgasYLRHUFHUTnEC3
      ▿ 1 : 2 elements
        - key : text
        - value : test
      ▿ 2 : 2 elements
        - key : timestamp
        - value : 1499914135546

但事实上它应该看起来像（如果你想访问字典[＆＃34;发件人＆＃34;]）：

▿ 2 elements
  ▿ 0 : 2 elements
    - key : sender
    - value : eGTYRSo81JefgasYLRHUFHUTnEC3
  ▿ 1 : 2 elements
    - key : text
    - value : test
  ▿ 2 : 2 elements
    - key : timestamp
    - value : 1499914135546

第一个解决方案：

您需要在查询中添加.child（＆＃34; -KotqLUUucaRagTRt967＆＃34;）。

或

第二个解决方案：

您需要做类似的事情：

query.observe(.childAdded, with: { snapshot in for child in snapshot.children { guard let value = child.value as? NSDictionary else { return } guard let sender = value["sender"] as? String else { return } // You can user the sender } })

更新：

query.observe(.childAdded, with: { snapshot in for child in snapshot.children.allObjects as! [FIRDataSnapshot] { if let value = child.value as? [String:Any], let sender = value["sender"] as? String { // You can user the sender } } })

注意

我将 observeSingleEvent 替换为观察，因为 Frank van Puffelen 说，这是 .childAdded的不常见组合

Answer 2

我认为你不想要一个ChildAdded处理程序，所以我使用observeSingleEvent示例，因为你想在没有触发器的情况下查询数据库中的数据。使用observeSingleEvent时，保持数据库同步非常重要。我建议使用以下代码：

p.para{
text-indent: 30px;
padding-left:15px;
}

Answer 3

正如 Pipiks 所解释的那样，您的问题是您尝试在高于返回数据的某个级别访问单个邮件详细信息。

快照值为您提供聊天消息的字典，其中顶级键是聊天消息键。要将返回的数据映射到消息数组，我将使用以下代码：

query.observeSingleEvent(of: .childAdded, with: { snapshot in

    guard let messagesDict = snapshot.value as? [String: AnyObject] else { return }

    self.messages = messagesDict.flatMap({ (messageId: String, messageData: Any) -> Message? in
        guard
            let sender = messageData["sender"] as? String,
            let text = messageData["text"] as? String,
            let timestamp = messageData["timestamp"] as? Int,
            let message = Message(key: messageKey, sender: sender, text: text, timestamp: timestamp) else {
                return nil
        }
        return message
    })

    self.tableView.reloadData()
})

这样做是将您的消息字典映射到Message个对象的数组。

我使用flatMap过滤掉任何没有发送者，文本或时间戳值的消息（因此flatMap返回一个[Message]对象）。

这是否解决了这个问题？

Firebase查询快照是否为零？

3 个答案: