Firebase查询快照为零? [英] Firebase Query snapshot nil?
问题描述
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一个tableView。查询返回一个快照,但是我无法正确地存储和加载数据。我从快照创建了一个字典,所以我可以得到个别的子值,但他们返回零:
$ p $
query.observeSingleEvent(of :.childAdded,其中:{快照在
打印(快照)
index indexs = self.messages.enumerated()。map {
IndexPath(row: $ 0.0,部分: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 timestamp = messagesDict [timestamp] as?Int else {return}
让message = Message.init(key:snapshot.key,sender:sender as!String,text:text as!String,timestamp:timestamp)
self.messages .append(消息)
self.tableView.reloadData()
})
po messagesDict
断点:$ b
$ b
▿1元素
▿0:2元素
- 键值:-KotqLUUucaRagTRt967
▿value:3元素
▿0:2元素
- key:发送者
- 值:eGTYRSo81JefgasYLRHUFHUTnEC3
▿1:2元素
- key:text
- value:测试
▿2:2元素
- key:时间戳
- 值:1499914135546
应用程序到达下一个断点,我设置 guard让sender
,但是应用程序点击返回并停止执行其余的代码块。如何正确访问发件人,文本和时间戳记元素,所以我可以将它们设置为变量,并将它们存储在我的表的数组?
任何帮助将不胜感激。我一直坚持这一段时间,我可以用另一双眼睛!
谢谢!!
<其他信息:
查询 b
let query = rootRef.child(chat-messages / \(chatKey))
数据库结构
{
chat-messages: {
-KotqKI4zF9cS5XMR9WU:{
-KotqLUUucaRagTRt967:{
sender:eGTYRSo81JefgasYLRHUFHUTnEC3,
text:test,
时间戳:1499914135546
}
},
-KotqvBoFFzOTY6Q1fO7:{
-KotqwGAJ85NuAp-Lh3Z:{
sender:eGTYRSo81JefgasYLRHUFHUTnEC3,
text:test,
timestamp:1499914290279
}
},
-KotsNgF0ou5MIDn2l5K:{
-KotsOSXw7OS_3xuXZgP: {
发件人: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:{
发件人:eGTYRSo81JefgasYLRHUFHUTnEC3,
text:test,
timestamp:1499914814205
},
-KotswHnzmfkEXih1O7y:{
sender :eGTYRSo81JefgasYLRHUFHUTnEC3,
text:test,
timestamp:1499914814 709
}
-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
$ b $ -b
$ -b
$发件人:$ e $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $'$' :1500746948396
-KpfUHQGuTDi4yZutS5K:{
sender:eGTYRSo81JefgasYLRHUFHUTnEC3,
text:test,
timestamp: 1500746950368
-KpfUHdSXeTzauATsDAP:{
sender:eGTYRSo81JefgasYLRHUFHUTnEC3,
text:test,
timestamp:1500746951277
},
-Kpfia0fXsoqpRtIr1kU:{
sender:eGTYRSo81JefgasYLRHUFHUTnEC3,
text:gerg,
timestamp:1500750962815
$ b $,
聊天参与者:{
-KotqKI4zF9cS5XMR9WU:{
eGTYRSo81JefgasYLRHUFHUTnEC3:{
username:tester
},
-KotqvBoFFzOTY6Q1fO7:{
eGTYRSo81JefgasYLRHUFHUTnEC3:{
username:tester
$ b $,
-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
}
}
},
用户邀请:{
eGTYRSo81JefgasYLRHUFHUTnEC3:{
36HDn5XyxjMCcMluJJ9KPBOCDMm1:{
username:tester2
}
}
},
users:{
36HDn5XyxjMCcMluJJ9KPBOCDMm1:{
email:tester2@test.com,
username:tester2
},
eGTYRSo81JefgasYLRHUFHUTnEC3:{
email:test@test.com,
username:tester
}
}
}
我不认为您需要ChildAdded处理程序,我去了一个observeSingleEvent例子,因为你想在没有触发器的情况下从数据库查询数据。当您使用observeSingleEvent时,保持数据库同步非常重要。我建议使用下面的代码: I'm creating a simple chat app to learn Swift and Firebase. I have a query that checks for a chat room's messages to load into a tableView. The query returns a snapshot but I'm having trouble getting the data to store and load it properly. I created a dictionary from the snapshot so I can get the individual child values but they are returning nil: The app gets to the next breakpoint where I set Any help would be greatly appreciated. I've been stuck on this for a while and I could use another pair of eyes! Thanks!! Additional info: Query: Database structure:
I do not think you want a ChildAdded handler, so I go with a observeSingleEvent example since you want to query data from the database at that time without triggers. When you use a observeSingleEvent, it is important to keep the database in sync. I would recommend using the code below:
这篇关于Firebase查询快照为零?的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!
$ p $ query.keepSynched(true)//保持数据与数据库同步,如果你有数据在你的appDelegate
query.observeSingleEvent(:.value,具有:{(snapshot)in //在这里更改
print(snapshot)
// // // //因为你想循环再次,因为可能有多个
在该聊天室中的消息,所有这些都有一个唯一的ID,做这个循环:
let enumerator = snapshot.children
while let rest = enumerator.nextObject( )as?FIRDataSnapshot {
//这里是单个消息
let values = rest.value as?NSDictionary
(key,value)in values {
print( Key:\(key),value:\(value))
}
//可以说你想检查一个名为text的键值是否为
让textUser = values?[text]为?S tring? 找不到文本
//如果没有文本,则提供默认值。你可以把它留空,比它是零(不推荐)
//这不仅是更多的可读性,我不使用强制解包,所以你的应用程序
//不能导致异常。
//从字典中获得更多值,就像我用textUser
// //初始化消息比这里一样。你会看到你不需要强制解开任何东西:D
$)
$ / code> pre> 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
returns data at the breakpoint:▿ 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
guard let sender
but the app hits return and stops executing the rest of the block of code. How do I properly access sender, text, and timestamp elements so I can set them to variables and store them in the array for my table?let query = rootRef.child("chat-messages/\(chatKey)")
{
"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"
}
}
}
query.keepSynched(true) //keeps data in sync with database, if you have data persistince on in your appDelegate
query.observeSingleEvent(of: .value, with: { (snapshot) in //notice the changed here
print(snapshot)
//Since you want to loop again because there could be multiple
//messages in that chatroom which all have a unique ID, do this loop:
let enumerator = snapshot.children
while let rest = enumerator.nextObject() as? FIRDataSnapshot {
//this is 1 single message here
let values = rest.value as? NSDictionary
for (key, value) in values{
print("Key: \(key), value: \(value)")
}
//lets say you want to check if there is a value with a key named "text":
let textUser = values?["text"] as? String ?? "No text found"
//providing a default value if there is no text. You could leave it empty, than it is nil (not recommend)
//Not only is this a lot more readable, I do not use force unwrapping so your app
//cannot cause an exception.
//Get more values from the dictionary as I did with textUser
//Initialize message than here. You will see you do not need to force unwrap anything :D
}
}
})