我尝试从我的数据库中进行提取以填充集合视图，按照最新的顺序填充到最旧的。我尝试使用snap.children.allObjects.reversed()，但我的应用在加载时崩溃了。这是完整的获取功能：
func fetchPosts() {
let ref = FIRDatabase.database().reference()
ref.child("users").queryOrderedByKey().observe(.value, with: { snapshot in
let users = snapshot.value as! [String : AnyObject]
for (_, value) in users {
if let uid = value["uid"] as? String {
if uid == FIRAuth.auth()?.currentUser?.uid {
if let followingUsers = value["following"] as? [String : String] {
for (_, user) in followingUsers {
self.following.append(user)
}
}
self.following.append(FIRAuth.auth()!.currentUser!.uid)
ref.child("posts").queryOrderedByKey().observeSingleEvent(of: .value, with: { (snap) in
for postSnapshot in snap.children.allObjects.reversed() as! [FIRDataSnapshot] {
let value = postSnapshot.value as! [String : AnyObject]
if let userID = value["userID"] as? String {
for each in self.following {
if each == userID {
let posst = Post()
if let poster = value["poster"] as? String, let likes = value["likes"] as? Int, let pathToImage = value["pathToImage"] as? String, let postID = value["postID"] as? String {
posst.poster = poster
posst.likes = likes
posst.pathToImage = pathToImage
posst.postID = postID
posst.userID = userID
if let people = value["peopleWhoLike"] as? [String : AnyObject] {
for (_, person) in people {
posst.peopleWhoLike.append(person as! String)
}
}
posts.append(posst)
}
}
}
self.collectionView.reloadData()
}
}
})
ref.removeAllObservers()
}
}
}
})
}
错误为EXC_BAD_INSTRUCTION (code=EXC_1386_INVOP, subcode=0x0)，警告来自＆＃39; ReversedRandomAccessCollection＆lt; [Any]＆gt;＆＃39; （又名＆＃39; ReversedRandomAccessCollection＆gt;＆＃39;）到不相关的类型＆＃39; [FIRDataSnapshot]＆＃39;总是失败。
.reversed不是解决这个问题的方法吗？实际上，我的代码没有.reversed按顺序加载帖子，从最顶层到底部最新。我该如何切换它？
编辑：帖子的Firebase片段：
"posts" : {
"-KfWzWv8rP38bUreDupj" : {
"likes" : 1,
"pathToImage" : "https://firebasestorage.googleapis.com/v0/b/cloudcamerattt.appspot.com/o/posts%2F1JSgke8QqFds4CxF2Z4MhuzbRoW2%2F-KfWzWv8rP38bUreDupj.jpg?alt=media&token=fef86bea-1ae2-4e1e-82fa-6209bc281a5e",
"peopleWhoLike" : {
"-KfX29jTcwaQDpkdIVX8" : "yI6NokUl2mTa7Uah4SgtAiulTJH2",
"-KfXQJBRemZUCI2ieT94" : "MpnGvQj7ZOdz12zKD0bTeX1kp0B3"
},
"postID" : "-KfWzWv8rP38bUreDupj",
"poster" : "Harry Potter",
"userID" : "1JSgke8QqFds4CxF2Z4MhuzbRoW2"
},
编辑2：添加时间戳
将var timestamp: Int!添加到我的Post对象，然后将其添加到我的上传功能中：
func uploadToFirebase() {
AppDelegate.instance().showActivityIndicator()
let uid = FIRAuth.auth()!.currentUser!.uid
let ref = FIRDatabase.database().reference()
let storage = FIRStorage.storage().reference(forURL: "gs://cloudcamerattt.appspot.com")
let key = ref.child("posts").childByAutoId().key
let imageRef = storage.child("posts").child(uid).child("\(key).jpg")
let data = UIImageJPEGRepresentation(self.previewImage.image!, 0.6)
var Timestamp: TimeInterval {
return NSDate().timeIntervalSince1970 * 1000
}
let uploadTask = imageRef.put(data!, metadata: nil) { (metadata, error) in
if error != nil {
print(error!.localizedDescription)
AppDelegate.instance().dismissActivityIndicator()
return
}
imageRef.downloadURL(completion: { (url, error) in
if let url = url {
let feed = ["userID" : uid,
"pathToImage" : url.absoluteString,
"likes" : 0,
"poster" : FIRAuth.auth()!.currentUser!.displayName!,
"postID" : key,
"timestamp" : (0-Timestamp)] as [String : Any]
let postFeed = ["\(key)" : feed]
ref.child("posts").updateChildValues(postFeed)
AppDelegate.instance().dismissActivityIndicator()
let feedController = self.storyboard?.instantiateViewController(withIdentifier: "feedVC") as! FeedViewController
feedController.navigationItem.setHidesBackButton(true, animated: false)
self.tabBarController?.selectedIndex = 0
}
})
}
uploadTask.resume()
}
然后将其添加到我的fetch中：
let posst = Post()
if let poster = value["poster"] as? String, let likes = value["likes"] as? Int, let pathToImage = value["pathToImage"] as? String, let postID = value["postID"] as? String, let timestamp = value["timestamp"] as? Int {
posst.poster = poster
posst.likes = likes
posst.pathToImage = pathToImage
posst.postID = postID
posst.userID = userID
posst.timestamp = timestamp
更新了抓取功能（导致崩溃Could not cast value of type 'FIRDataSnapshot' (0x10584eee8) to 'NSArray' (0x107b43dd8).）：
func fetchPosts() {
let ref = FIRDatabase.database().reference()
ref.child("users").queryOrderedByKey().observe(.value, with: { snapshot in
let users = snapshot.value as! [String : AnyObject]
for (_, value) in users {
if let uid = value["uid"] as? String {
if uid == FIRAuth.auth()?.currentUser?.uid {
if let followingUsers = value["following"] as? [String : String] {
for (_, user) in followingUsers {
self.following.append(user)
}
}
self.following.append(FIRAuth.auth()!.currentUser!.uid)
for child in snapshot.children.reversed() {
let snap = child as! [FIRDataSnapshot]
ref.child("posts").queryOrdered(byChild: "timestamp").observeSingleEvent(of: .value, with: { (snap) in
if let userID = value["userID"] as? String {
for each in self.following {
if each == userID {
let posst = Post()
if let poster = value["poster"] as? String, let likes = value["likes"] as? Int, let pathToImage = value["pathToImage"] as? String, let postID = value["postID"] as? String, let timestamp = value["timestamp"] as? Int {
posst.poster = poster
posst.likes = likes
posst.pathToImage = pathToImage
posst.postID = postID
posst.userID = userID
posst.timestamp = timestamp
if let people = value["peopleWhoLike"] as? [String : AnyObject] {
for (_, person) in people {
posst.peopleWhoLike.append(person as! String)
}
}
posts.append(posst)
}
}
}
self.collectionView.reloadData()
}
})
}
ref.removeAllObservers()
}
}
}
})
}
答案 0 :(得分：1)
尝试
for child in snapshot.children.reversed() {
let snap = child as! FIRDataSnapshot
print(snap)
}
您按键排序，将最旧的加载到最新。如果您想要撤销订单，让Firebase执行繁重的工作，请使用此处发布的反向时间顺序技术
In Firebase, how can I query the most recent 10 child nodes?
然后很容易进行反向查询...
"posts" : {
"-KfWzWv8rP38bUreDupj" : {
"likes" : 1,
"pathToImage" : "https:/...",
"peopleWhoLike" : {
"-KfX29jTcwaQDpkdIVX8" : "yI6NokUl2mTa7Uah4SgtAiulTJH2",
"-KfXQJBRemZUCI2ieT94" : "MpnGvQj7ZOdz12zKD0bTeX1kp0B3"
},
"postID" : "-KfWzWv8rP38bUreDupj",
"poster" : "Harry Potter",
"timestamp" : -1.46081635550362E12, //Just add this child
"userID" : "1JSgke8QqFds4CxF2Z4MhuzbRoW2"
},
然后
ref.child("posts").queryOrdered(byChild: "timestamp").observe(...
此外，作为孩子可能不需要重复的postID，因为它也是帖子的关键。
答案 1 :(得分：0)
你是正确的，你需要在某处投射某些东西，因为Swift只知道我们从Any数组开始。问题是你在错误的地方投错了。在for循环内部的开头转换postSnapshot。
弄清楚这种事情的方法是制作一个简化的游乐场示例。你正在做相同的事情：
let arr : [Any] = [1,2,3]
for i in arr.reversed() as! [Int] { // crash
}
然而，我们在该示例中所知道的并不是arr.reversed();是i是一个Int。这很好：
let arr : [Any] = [1,2,3]
for i in arr.reversed() {
if let i = i as? Int {
// now it is safe to use `i`
}
}
你的情况是平行的。在for循环开始时，您需要将postSnapshot强制转换为FIRDataSnapshot。现在你可以继续了。