I'm trying to create a feed that should include posts made by people a user follows, and I'm using following function to get posts for user feed:
func observePosts(for userID: String, completion: #escaping ([UserPost], String) -> Void) {
let databaseKey = "Posts/\(userID)/"
databaseRef.child(databaseKey).queryOrderedByKey().queryLimited(toLast: 12).observe(.value) { snapshot in
var retrievedPosts = [UserPost]()
var lastSeenPostKey = ""
let dispatchGroup = DispatchGroup()
for snapshotChild in snapshot.children.reversed() {
guard let postSnapshot = snapshotChild as? DataSnapshot,
let postDictionary = postSnapshot.value as? [String: Any]
else {
print("Couldn't cast snapshot as DataSnapshot")
return
}
dispatchGroup.enter()
lastSeenPostKey = postSnapshot.key
do {
let jsonData = try JSONSerialization.data(withJSONObject: postDictionary as Any)
let decodedPost = try JSONDecoder().decode(UserPost.self, from: jsonData)
UserService.shared.observeUser(for: decodedPost.userID) { postAuthor in
decodedPost.author = postAuthor
retrievedPosts.append(decodedPost)
dispatchGroup.leave()
}
} catch {
print("Couldn't create UserPost from postDictionary")
}
}
dispatchGroup.notify(queue: .main) {
completion(retrievedPosts, lastSeenPostKey)
}
}
}
First step I'm getting user feed posts with .observe function and after that I'm iterating through every received post calling a UserService.shared.observeUser method that observes user data for every post to set post author's profile picture and username.
The problem with my method is that I'm using DispatchGroup's .enter and .leave methods to notify once every observe function got user data so that I could call completion block in which I'm reloading tableView.
Sure it works fine first time but since it's observe function it's called every time there's a change to user so once user updates his data (profile pic, usernama etc.) it crashes on dispatchGroup.leave() line since it's not balanced with dispatchGroup.enter()
What would be a correct approach to solve this issue?
I've been trying to solve this problem for 3 days searching all the internet, and only advice I found is to fetch it one time using observeSingleValue() instead of observing, but I really need to observe user profile data to keep profile pics and other necessary data up to date.
Related
I've never really gotten the nuances of async operations so time and again, I get stymied. And I just can't figure it out.
I'm trying to do some very simple web scraping.
My local volleyball association has a page (verbose HTML, not responsive, not mobile-friendly, yaddah, yaddah, yaddah) which shows the refs assigned to each game of the season. I'm trying to write a silly little app which will scrape that page (no API, no direct access to db, etc.) and display the data in a grouped table. The first group will show today's matches (time, home team, away team). The second group will show tomorrow's matches. Third group shows the entire season's matches.
Using code I found elsewhere, my viewDidLoad loads the page, scrapes the data and parses it into an array. Once I've parsed the data, I have three arrays: today, tomorrow, and matches, all are [Match].
override func viewDidLoad() {
super.viewDidLoad()
let url = URL(string: urlString)!
let request = NSMutableURLRequest(url: url)
let task = URLSession.shared.dataTask(with: request as URLRequest) {
data, response, error in
if let error = error {
print (error)
} else {
if let unwrappedData = data {
// scrape, scrape, parse, parse
matchRow = ...
self.matches.append(matchRow)
if matchRow.date == todaysDate {
self.today.append(matchRow)
} else if matchRow.date == tomorrowsDate {
self.tomorrow.append(matchRow)
}
}
}
}
task.resume()
}
As I'm sure is no surprise to anyone who understands async operations, my table is empty. I've checked and I see the the data is there and properly parsed, etc. But I can't for the life of me figure out how get the data in my table. The way I have it now, the data is not ready when numberOfSections or numberOfRowsInSection is called.
I've found the Ray Wenderlich tutorial on URLSession and I also have a Udemy course (Rob Percival) that builds an app to get the weather using web scraping, but in both those instances, the app starts and waits for user input before going out to the web to get the data. I want my app to get the data immediately upon launch, without user interaction. But I just can't figure out what changes I need to make so that those examples work with my program.
Help, please.
You can simply reload the tableviews once the data arrays are getting populated from the URLSession completion block. Have you tried that. Sample snippet may be like the one follows.
let task = URLSession.shared.dataTask(with: request as URLRequest) {
data, response, error in
if let error = error {
print (error)
} else {
if let unwrappedData = data {
// scrape, scrape, parse, parse
matchRow = ...
self.matches.append(matchRow)
if matchRow.date == todaysDate {
self.today.append(matchRow)
} else if matchRow.date == tomorrowsDate {
self.tomorrow.append(matchRow)
}
}
DispatchQueue.main.async { [weak self] in
self?.todayTableView.reloadData()
self?.tomorrowTableView.reloadData()
}
}
}
I am new to Realm DataBase and I need a way to read data from realmCloud, but from two different app projects. The way I have tried to implement this is by using query-synced realm. At the moment I'm using a singe realm user to write the data in one app, and the same realm user to read data from another app. The problem is that making a query from the second app(the one used for reading) doesn't return any realm objects ( I have also noticed that user identifier is different from the first one, and also the user permissions are nil.
I have tried setting permissions directly from RealmStudio since documentation is not precise on how to set them from code
func openRealm() {
do {
realm = try Realm(configuration: SyncUser.current!.configuration())
let queryResults = realm.objects(*className*.self)
let syncSubscription = queryResults.subscribe()
let notificationToken = queryResults.observe() { [weak self] (changes) in
switch (changes) {
case .initial: print(queryResults)
case .error(let error): print(error)
default: print("default")
}
}
for token in queryResults {
print(token.tokenString)
}
syncSubscription.unsubscribe()
notificationToken.invalidate()
} catch {
print(error)
}
}
This function prints the data in one app project, but used in another app project with the same user logged in, and the same classFile referenced in the project, it does not. (note that SyncUser.current.identifier is different also
There are a couple of issues.
Some of these calls are asynchronous and the code in your question is going out of scope before the data is sync'd (retreived). The bottom line is code is faster than the internet and you need to design the flow of the app around async calls; don't try to work with the data until it's available.
For example
let notificationToken = queryResults.observe() { [weak self] (changes) in
//here is where results are fully populated
}
// this code may run before results are populated //
for token in queryResults {
print(token.tokenString)
}
Also, let notificationToken is a local var and goes out of scope before the results are populated as well.
These issues are super easy to fix. First is to keep the notification token alive while waiting for results to be populated and the second is to work with the results inside the closure, as that's when they are valid.
var notificationToken: NotificationToken? = nil //a class var
func openRealm() {
do {
let config = SyncUser.current?.configuration()
let realm = try Realm(configuration: config!)
let queryResults = realm.objects(Project.self)
let syncSubscription = queryResults.subscribe(named: "my-projects")
self.notificationToken = queryResults.observe() { changes in
switch changes {
case .initial:
print("notification: initial results are populated")
queryResults.forEach { print($0) }
case .update(_, let deletions, let insertions, let modifications):
print("notification: results, inserted, deleteed or modified")
insertions.forEach { print($0) } //or mods or dels
case .error(let error):
fatalError("\(error)")
}
}
} catch {
print(error)
}
}
deinit {
self.notificationToken?.invalidate()
}
The other advantage of keeping that token (and its corresponding code) alive is when there are further changes, your app will be notified. So if another project is added for example, the code in the 'changes' section will run and display that change.
I have been stuck for a while now and any advice would be greatly appreciated. I am creating an app that uses Firebase database and I have created 5 classes that hold different data in Firebase. I'm creating a tableview that needs to display information from each of the 5 classes (Profile name, image, then information about a league, and info about scores). So in my new class I created a function calling for data from firebase from each class...
For example: GET all players from X league {
FOR every player in the league {
GET the players information
THEN GET the scores
THEN on and on
once we have all information APPEND to new array
}
and then rank the array
}
After all this runs I want to reload the table view on the VC
SO my solution works on the original load but if I back out and re enter the screen the names and images repeat.
To be exact when the indexes print to the console I get
"Player 1: Zack"
"Player 2: John"
However, the screen shows John's image and name repeatedly. BUT only that class... All other data stays where it is supposed to be. And the original functions are all written the same way.
I'm thinking it's something to do with memory management or I wrote my completion handler poorly?
Here is the code in the new array class:
You'll also notice that my completion() is inside my for in loop which I HATE but it's the only way I could get the function to finish before completing.. Otherwise the function completes before the data is ready.
func getLeaderboard(leagueID: String, completion: #escaping ()->()) {
print("League Count After removeAll \(self.rankedGolfers.count)")
self.leagueMembers.getLeagueMembers(leagueID: leagueID) {
print("HANDLER: Step 1: Get League Members")
for member in self.leagueMembers.leagueMembers {
print("Golfer Member ID: \(member.userID)")
self.golferInfo.getGolferInfo(userKey: member.userID, completion: {
print("HANDLER: Step 2: Get player profile info")
print("Golfer Name3: \(self.golferInfo.golfers[0].firstName) \(self.golferInfo.golfers[0].lastName)")
self.handicapHelper.getRounds(userID: member.userID, completion: {
print("HANDLER: Step 3: Get players Handicap")
print("Golfer Handicap3: \(self.golferInfo.golfers[0].lastName): \(self.handicapHelper.handicap)")
self.leagueInfo.getLeagueInfo(leagueID: leagueID, completion: {
print("HANDLER: Step 4: Get league info")
let golferIndex = self.golferInfo.golfers[0]
let memberInfoIndex = self.leagueInfo.leagueInfo[0]
let golferID = member.userID
let profileImg = golferIndex.profileImage
let golferName = "\(golferIndex.firstName) \(golferIndex.lastName)"
let handicap = self.handicapHelper.handicap
let golferLeaguePardieScore = member.pardieScore
let leagueRoundsPlayed = member.numberOfRounds
let roundsRemaining = memberInfoIndex.leagueMinRounds - leagueRoundsPlayed
let currentWinnings = member.currentWinnings
let newGolfer = Leaderboard(golferID: golferID, profileImg: profileImg ?? "No Img", golferName: golferName, golferHandicap: handicap, golferLeaguePardieScore: golferLeaguePardieScore, roundsPlayedInLeague: leagueRoundsPlayed, roundsRemaining: roundsRemaining, currentWinnings: currentWinnings)
self.rankedGolfers.append(newGolfer)
print("HANDLER: Step 5: Add golfer to array")
//print("Golfer Name 4: \(newGolfer.golferName)")
//print("Rounds Remaining: \(newGolfer.roundsRemaining)")
print("league Member Count: \(self.rankedGolfers.count)")
self.getLeaderboardRanking()
print("HANDLER: Step 6: Rank Array")
//print("COMPLETION: \(self.rankedGolfers.count)")
completion()
})
})
})
}
}
}
Thank you for any help possible!
I think we can solve this with a DispatchGroup, which will ensure all of the data is loaded for each user, then append the user to an array used as a tableView dataSource and then reload the tableView upon completion.
To keep it simple we'll start with a UserInfo class which stores their uid, name, favorite food and handicap.
class UserInfoClass {
var uid = ""
var name = ""
var favFood = ""
var handicap = 0
}
and a class var array used as the dataSource for the tableView
var userInfoArray = [UserInfoClass]()
Then, assuming we have a structure like this...
users
uid_0
name: "Leroy"
handicaps
uid_0
amt: 4
fav_foods
uid_0
fav_food: "Pizza"
...here's a function that reads all users, then iterates over each one populating a UserInfoClass with their name and uid, as well as creating a dispatch group that also populates their favorite food and handicap. When that's complete the user is added to the dataSource array and when all of the users are read the tableView is reloaded to display the information.
func loadUsersInfoAndHandicap() {
let ref = self.ref.child("users")
self.userInfoArray = []
ref.observeSingleEvent(of: .value, with: { snapshot in
let group = DispatchGroup()
let allUsers = snapshot.children.allObjects as! [DataSnapshot]
for user in allUsers {
let uid = user.key
let name = user.childSnapshot(forPath: "name").value as? String ?? "No Name"
let aUser = UserInfoClass()
aUser.uid = uid
aUser.name = name
group.enter()
self.loadFavFood(withUid: uid) {favFood in
aUser.favFood = favFood
group.leave()
}
group.enter()
self.loadHandicap(withUid: uid) { handicap in
aUser.handicap = handicap
group.leave()
}
group.notify(queue: .main) {
self.userInfoArray.append(aUser)
}
}
group.notify(queue: .main) {
print("done, reload the tableview")
for user in self.userInfoArray {
print(user.uid, user.name, user.favFood, user.handicap)
}
}
})
}
the users name and uid is read from the main users node and here are the two functions that read their favorite food and handicap.
func loadFavFood(withUid: String, completion: #escaping(String) -> Void) {
let thisUser = self.ref.child("userInfo").child(withUid)
thisUser.observeSingleEvent(of: .value, with: { snapshot in
let food = snapshot.childSnapshot(forPath: "fav_food").value as? String ?? "No Fav Food"
completion(food)
})
}
func loadHandicap(withUid: String, completion: #escaping(Int) -> Void) {
let thisUser = self.ref.child("handicaps").child(withUid)
thisUser.observeSingleEvent(of: .value, with: { snapshot in
let handicap = snapshot.childSnapshot(forPath: "amt").value as? Int ?? 0
completion(handicap)
})
}
note that self.ref points to my firebase so substitute a reference to your firebase.
Note I typed this up very quickly and there is essentially no error checking so please add that accordingly.
I'm trying to get data from my database and after obtaining a piece of data, using that piece of data to find a new piece of data.
At the end, I can piece these together and return the derived data. I'm not sure this is the best way to approach this, but this is where im at as of now.
My problem is that each call to the database (Firebase) is async and therefore I need to somehow wait for the async to finish, before going on.
I've looked at dispatch group and heres what I have so far:
let taskGroup = DispatchGroup()
for buildingKey in building.allKeys
{
var aprt = NSDictionary()
taskGroup.enter()
// ASYNC REQUEST
getAbodesWithUID(UID: buildingKey as! String, callback: { (success, abodes) in
aprt = abodes
taskGroup.leave()
})
taskGroup.enter()
for key in aprt.allKeys
{
// ASYNC REQUEST
getTenantsWithAprt(UID: key as! String, callback: { (success, user) in
for userKey in user.allKeys
{
let dict = NSMutableDictionary()
dict.setValue(((building[buildingKey] as? NSDictionary)?["Address"] as? NSDictionary)?.allKeys[0] as? String, forKey: "Building")
dict.setValue((user[userKey] as? NSDictionary)?["Aprt"], forKey: "Number")
dict.setValue((user[userKey] as? NSDictionary)?["Name"], forKey: "Name")
dict.setValue(userKey, forKey: "UID")
dict.setValue((user[userKey] as? NSDictionary)?["PhoneNumber"], forKey: "Phone")
apartments.append(dict)
}
taskGroup.leave()
})
}
}
taskGroup.notify(queue: DispatchQueue.main, execute: {
print("DONE")
callback(true, apartments)
})
I can't seem to get it to callback properly
First, you should be iterating over aprt.allKeys inside of the callback for getAbodesWithUID, other wise, when the for loop executes aprt will be an empty dictionary.
Secondly, the taskGroup.enter() call above that for loop should be inside of the for loop, because it needs to be called once for every key. It should be placed where the // ASYNC REQUEST comment currently is.
This is precisely what "promises" are for is for. They are available in Swift via a 3rd party add-in. A popular way to do this is to push all your reads/gets into an array. Then you promise.all(yourArray) which returns the array of results/values that you then iterate over to get at each one.
From this other answer:
You can look into when which may provide what you need and is covered
here.
Use the loop to put your promises into an array and then do something
like this:
when(fulfilled: promiseArray).then { results in
// Do something
}.catch { error in
// Handle error
}
I just want to ask about firebase retrieve data. How can i handle firebase retrieve data finished? I don't see any completion handler.
I want to call some function after this firebase data retrieve finished. How can i handle???
DataService.ds.POST_REF.queryOrderedByChild("created_at").observeEventType(.ChildAdded, withBlock: { snapshot in
if let postDict = snapshot.value as? Dictionary<String, AnyObject> {
let postKey = snapshot.key
let post = Post(postKey: postKey, dictionary: postDict)
self.posts.append(post)
}
})
In Firebase, there isn't really a concept of 'finished' (when listening to 'child added'). It is just a stream of data (imagine someone adds a new record before the initial data is 'finished'). You can use the 'value' event to get an entire object, but that won't give you new records as they're added like 'child added' does.
If, you really need to use child added and get notified when it's probably finished, you can set a timer. I don't know swift, but here's the logic.
Set up your 'child added' event.
Set a timer to call some finishedLoading() function in 500ms.
Each time the 'child added' event is triggered, destroy the timer set in step two and create another one (that is, extend it another 500ms).
When new data stops coming in, the timer will stop being extended and finsihedLoading() will be called 500ms later.
500ms is just a made up number, use whatever suits.
Do one request for SingleEventOfType(.Value). This will give you all info initially in one shot, allowing you to then do whatever function you want to complete once you have that data.
You can create a separate query for childAdded and then do anything there you want to do when a new post has been added
Write your entire block of code in a function which has a completion handler like so:
func aMethod(completion: (Bool) -> ()){
DataService.ds.POST_REF.queryOrderedByChild("created_at").observeEventType(.ChildAdded, withBlock: { snapshot in
if let postDict = snapshot.value as? Dictionary<String, AnyObject> {
let postKey = snapshot.key
let post = Post(postKey: postKey, dictionary: postDict)
self.posts.append(post)
}
completion(true)
})
}
Then call it somewhere like so:
aMethod { success in
guard success == true else {
//Do something if some error occured while retreiving data from firebase
return
}
//Do something if everything went well.
.
.
.