I am building arrays via a for in loop inside a closure, then passing these arrays through a segue. I am able to print the contents of the arrays from within the closure, but when I access the array from outside, it is always empty.
I have tried to use .reloadData() to update the arrays outside of the closure, but I can't seem to get it quite right. Does anyone know if this is the correct approach?
Here is my code:
var distances: [Double]
var journeyTimes: [Double]
directions.calculate { response, error in
if let route = response?.routes.first {
print("Distance: \(route.distance/1000) km, ETA: \(route.expectedTravelTime/60) mins")
self.distances.append(route.distance/1000)
self.journeyTimes.append(route.expectedTravelTime/60)
print(self.distances)
print(self.journeyTimes)
} else {
print("Error!")
} updateArrays()
}
func updateArrays() {
self.collectionView.reloadData()
}
The print statements above produce results, and my prepare for segue carries distances and journeyTimes through, but they are always empty when I try to access them.
I think I need to update the distances and journeyTimes arrays before prepare for segue, outside of the closure, but I don't know how to do it.
Grateful for any help on this
Thanks
One way to address this is by using a Dispatch Group. Create a new constant:
let myDispatchGroup = DispatchGroup()
var distances: [Double]
var journeyTimes: [Double]
Just before you make your network call add:
myDispatchGroup.enter()
Make sure you add it before the asynch network call begins.
After your arrays have been fully updated and your are about to exit your Asynchronous network call add:
self.myDispatchGroup.leave()
Only after the number of enters and leaves on the myDispatchGroup are equal will this function be called. Add it just before you perform your segue
func yourFunctionThatCallsSegue() {
myDispatchGroup.notify(queue: DispatchQueue.main) {
let destinationViewController = segue.destination as! YourDestinationViewController
destinationViewController.distances = self.distances // you are in a dispatch group closure
destinationViewController.journeyTimes = self.journeyTimes
performSegue(withIdentifier: "Your Identifier", sender: AnyClass.self)
}
}
Related
I honestly I have tried to figure out when to call ref.removeAllObservers or ref.removeObservers, but I'm confused. I feed I'm doing something wrong here.
var noMoreDuplicators = [String]()
func pull () {
if let myIdi = FIRAuth.auth()?.currentUser?.uid {
let ref = FIRDatabase.database().reference()
ref.child("users").queryOrderedByKey().observe(.value, with: { snapshot in
if let userers = snapshot.value as? [String : AnyObject] {
for (_, velt) in userers {
let newUser = usera()
if let thierId = velt["uid"] as? String {
if thierId != myIdi {
if let userName = velt["Username"] as? String, let name = velt["Full Name"] as? String, let userIdent = velt["uid"] as? String {
newUser.name = name
newUser.username = userName
newUser.uid = userIdent
if self.noMoreDuplicators.contains(userIdent) {
print("user already added")
} else {
self.users.append(newUser)
self.noMoreDuplicators.append(userIdent)
}
}
}
}
}
self.tableViewSearchUser.reloadData()
}
})
ref.removeAllObservers()
}
}
Am I only supposed to call removeAllObservers when observing a single event, or...? And when should I call it, if call it at all?
From official documentation for observe(_:with:) :
This method is used to listen for data changes at a particular location. This is
the primary way to read data from the Firebase Database. Your block
will be triggered for the initial data and again whenever the data
changes.
Now since this method will be triggered everytime the data changes, so it depends on your usecase , if you want to observe the changes in the database as well, if not then again from the official documentation:
Use removeObserver(withHandle:) to stop receiving updates.
Now if you only want to observe the database once use observeSingleEvent(of:with:) , again from official documentation:
This is equivalent to observe:with:, except the block is
immediately canceled after the initial data is returned
Means that you wont need to call removeObserver(withHandle:) for this as it will be immediately canceled after the initial data is returned.
Now lastly , if you want to remove all observers , you can use this removeAllObserver but note that:
This method removes all observers at the current reference, but does
not remove any observers at child references. removeAllObservers must
be called again for each child reference where a listener was
established to remove the observers
Actually, you don't need to call removeAllObservers when you're observing a single event, because this observer get only called once and then immediately removed.
If you're using observe(.value) or observe(.childAdded), and others though, you would definitely need to remove all your observers before leaving the view to preserve your battery life and memory usage.
You would do that inside the viewDidDisappear or viewWillDisappear method, like so:
override func viewWillDisappear(_ animated: Bool) {
super.viewWillDisappear(animated)
// Remove your observers here:
yourRef.removeAllObservers()
}
Note: you could also use removeObserver(withHandle:) method.
I have a tabBar controller with 2 tabs: tabA which contains ClassA and tabB which contains ClassB. I send data to Firebase Database in tabA/ClassA and I observe the Database in tabB/ClassB where I retrieve it and add it to a tableView. Inside the tableView's cell I show the number of sneakers that are currently inside the database.
I know the difference between .observeSingleEvent( .value) vs .observe( .childAdded). I need live updates because while the data is getting sent in tabA, if I switch to tabB, I want to to see the new data get added to the tableView once tabA/ClassA is finished.
In ClassB I have my observer in viewWillAppear. I put it inside a pullDataFromFirebase() function and every time the view appears the function runs. I also have Notification observer that listens for the data to be sent in tabA/ClassA so that it will update the tableView. The notification event runs pullDataFromFirebase() again
In ClassA, inside the callback of the call to Firebase I have the Notification post to run the pullDataFromFirebase() function in ClassB.
The issue I'm running into is if I'm in tabB while the new data is updating, when it completes, the cell that displays the data has a count and the count is thrown off. I debugged it and the the sneakerModels array that holds the data is sometimes duplicating and triplicating the newly added data.
For example if I am in Class B and there are 2 pairs of sneakers in the database, the pullDataFromFirebase() func will run, and the tableView cell will show "You have 2 pairs of sneakers"
What was happening was if I switched to tabA/ClassA, then added 1 pair of sneakers, while it's updating I switched to tabB/ClassB, the cell would still say "You have 2 pairs of sneakers" but then once it updated the cell would say "You have 5 pairs of sneakers" and 5 cells would appear? If I switched tabs and came back it would correctly show "You have 3 pairs of sneakers" and the correct amount of cells.
That's where the Notification came in. Once I added that if I went through the same process and started with 2 sneakers the cell would say "You have 2 pairs of sneakers", I go to tabA, add another pair, switch back to tabB and still see "You have 2 pairs of sneakers". Once the data was sent the cell would briefly show "You have 5 pairs of sneakers" and show 5 cells, then it would correctly update to "You have 3 pairs of sneakers" and the correct amount of cells (I didn't have to switch tabs).
The Notification seemed to work but there was that brief incorrect moment.
I did some research and the most I could find were some posts that said I need to use a semaphore but apparently from several ppl who left comments below they said semaphores aren't meant to be used asynchronously. I had to update my question to exclude the semaphore reference.
Right now I'm running tableView.reloadData() in the completion handler of pullDataFromFirebase().
How do I reload the tableView outside of the observer once it's finished to prevent the duplicate values?
Model:
class SneakerModel{
var sneakerName:String?
}
tabB/ClassB:
ClassB: UIViewController, UITableViewDataSource, UITableViewDelegate{
var sneakerModels[SneakerModel]
override func viewDidLoad() {
super.viewDidLoad()
NotificationCenter.default.addObserver(self, selector: #selector(pullDataFromFirebase), name: NSNotification.Name(rawValue: "pullFirebaseData"), object: nil)
}
override func viewWillAppear(_ animated: Bool){
super.viewWillAppear(animated)
pullDataFromFirebase()
}
func pullDataFromFirebase(){
sneakerRef?.observe( .childAdded, with: {
(snapshot) in
if let dict = snapshot.value as? [String:Any]{
let sneakerName = dict["sneakerName"] as? String
let sneakerModel = SneakerModel()
sneakerModel.sneakerName = sneakerName
self.sneakerModels.append(sneakerModel)
//firebase runs on main queue
self.tableView.reloadData()
}
})
}
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return sneakerModels.count
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "SneakerCell", for: indexPath) as! SneakerCell
let name = sneakerModels[indePath.row]
//I do something else with the sneakerName and how pairs of each I have
cell.sneakerCount = "You have \(sneakerModels.count) pairs of sneakers"
return cell
}
}
}
tabA/ClassA:
ClassA : UIViewController{
#IBAction fileprivate func postTapped(_ sender: UIButton) {
dict = [String:Any]()
dict.updateValue("Adidas", forKey: "sneakerName")
sneakerRef.?.updateChildValues(dict, withCompletionBlock: {
(error, ref) in
//1. show alert everything was successful
//2. post notification to ClassB to update tableView
NotificationCenter.default.post(name: Notification.Name(rawValue: "pullFirebaseData"), object: nil)
}
}
}
In other parts of my app I use a filterDuplicates method that I added as an extension to an Array to filter out duplicate elements. I got it from filter array duplicates:
extension Array {
func filterDuplicates(_ includeElement: #escaping (_ lhs:Element, _ rhs:Element) -> Bool) -> [Element]{
var results = [Element]()
forEach { (element) in
let existingElements = results.filter {
return includeElement(element, $0)
}
if existingElements.count == 0 {
results.append(element)
}
}
return results
}
}
I couldn't find anything particular on SO to my situation so I used the filterDuplicates method which was very convenient.
In my original code I have a date property that I should've added to the question. Any way I'm adding it here and that date property is what I need to use inside the filterDuplicates method to solve my problem:
Model:
class SneakerModel{
var sneakerName:String?
var dateInSecs: NSNumber?
}
Inside tabA/ClassA there is no need to use the Notification inside the Firebase callback however add the dateInSecs to the dict.
tabA/ClassA:
ClassA : UIViewController{
#IBAction fileprivate func postTapped(_ sender: UIButton) {
//you must add this or whichever date formatter your using
let dateInSecs:NSNumber? = Date().timeIntervalSince1970 as NSNumber?
dict = [String:Any]()
dict.updateValue("Adidas", forKey: "sneakerName")
dict.updateValue(dateInSecs!, forKey: "dateInSecs")//you must add this
sneakerRef.?.updateChildValues(dict, withCompletionBlock: {
(error, ref) in
// 1. show alert everything was successful
// 2. no need to use the Notification so I removed it
}
}
}
And in tabB/ClassB inside the completion handler of the Firebase observer in the pullDataFromFirebase() function I used the filterDuplicates method to filter out the duplicate elements that were showing up.
tabB/ClassB:
func pullDataFromFirebase(){
sneakerRef?.observe( .childAdded, with: {
(snapshot) in
if let dict = snapshot.value as? [String:Any]{
let sneakerName = dict["sneakerName"] as? String
let sneakerModel = SneakerModel()
sneakerModel.sneakerName = sneakerName
self.sneakerModels.append(sneakerModel)
// use the filterDuplicates method here
self.sneakerModels = self.sneakerModels.filterDuplicates{$0.dateInSecs == $1.dateInSecs}
self.tableView.reloadData()
}
})
}
Basically the filterDuplicates method loops through the sneakerModels array comparing each element to the dateInSecs and when it finds them it excludes the copies. I then reinitialize the sneakerModels with the results and everything is well.
Also take note that there isn't any need for the Notification observer inside ClassB's viewDidLoad so I removed it.
I have two viewControllers that are giving me trouble. One is called notificationAccessViewController.swift and the other is called classChooseViewController.swift. I have a button in the notificationAccessViewController that triggers a segue to the classChooseViewController. What I need to do is within the prepareForSegue function, perform an Alamofire request and then pass the response to the classChooseViewController. That works! BUT, not fast enough.
Below is my prepareForSegue function within the notificationAccessViewController
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
let DestViewController = segue.destination as! classChooseViewController
Alamofire.request("MYURL.com").responseJSON { (response) in
if let JSON : NSDictionary = response.result.value as! NSDictionary?{
let classNameArray = JSON["className"] as! NSArray
print("---")
print(classNameArray)
DestViewController.classNameArray = classNameArray
}
}
}
I have it printing out classNameArray to the console, which it does SUCCESSFULLY. Although, in my classChooseViewController.swift, I also print out the classNameArray to the console and it prints with nothing inside of it. This is because the viewDidLoad() function of the classChooseViewController.swift is running before the prepareForSegue function has finished. I want to know what I can do to ensure that the classChooseViewController does not load until the prepareForSegue function has FINISHED running.
Below is my code for classChooseViewController
class classChooseViewController: UIViewController, UITableViewDelegate, UITableViewDataSource {
var classNameArray: NSArray = []
override func viewDidLoad() {
super.viewDidLoad()
print(classNameArray)
}
}
I have attached a picture of what the console reads. You can see that the classNameArray prints from the classChooseViewControllers viewDidLoad() function BEFORE the prepareForSegue() function because the "---" prints out after.
Your design is wrong.
The Alamofire request function is asynchronous. It returns immediately, before the results are ready. Then it invokes the completion handler that you pass in.
I tend to agree with Paul that you should make the request in the destination view controller, not in the current view controller.
If you DO want to fetch the data in Alamofire before you segue to the other view controller then you'll need to write a method that starts the request, then invokes the segue to the other view controller from the Alamofire.request() call's completion handler.
If you're invoking the new view controller from a button press, you need to not link the button directly to a segue, but instead write an IBAction method that triggers the AlamoFire request call, then invokes the segue (or instantiates the view controller directly and pushes/presents it manually) from the completion handler.
Something like this:
#IBAction buttonAction(sender: UIButton) {
Alamofire.request("MYURL.com").responseJSON {
(response) in
if let JSON : NSDictionary = response.result.value as! NSDictionary? {
let classNameArray = JSON["className"] as! NSArray
print("---")
print(classNameArray)
let theClassChooseViewController = storyboard.instantiateViewController(withIdentifier:"ClassChooseViewController" as ClassChooseViewController
theClassChooseViewController.classNameArray = classNameArray
presentViewController(theClassChooseViewController,
animated: true,
completion: nil)
}
}
}
By the way, class names and types should start with an upper case letter, and variable names should start with a lower-case letter. This is a very strong convention in both Swift and Objective-C, and you'll confuse the hell out of other iOS/Mac developers unless you follow the convention.
I have static data (3 values) coming from CloudKit, and the problem is when I refresh the UITableView, I get 6 values instead of 3 values.
I'm not sure why it doesn't refresh and throw out old data from the Array, but instead it keeps the old data and adds the same data to it Array.
Initial UITableView set up:
func getData() {
cloud.getCloudKit { (game: [Game]) in
var teamColorArray = [String]()
for item in game {
let itemColor = item.teamColor
teamColorArray.append(itemColor)
print("TCA in: \(teamColorArray)")
}
self.teamColorArray = teamColorArray
self.tableView.reloadData()
}
}
Prints: ["CC0033", "FDB927", "E3263A"]
Refresh data when UIRefreshControl pulled:
#IBAction func refreshData(_ sender: Any) {
self.teamColorArray.removeAll()
getData()
self.refreshControl?.endRefreshing()
}
Prints: ["CC0033", "FDB927", "E3263A", "CC0033", "FDB927", "E3263A"]
I think I have it narrowed down to somehow game in the function getData() is incremented to a count of 6 items. I'm not sure why it wouldn't always stay at 3 items if it were pulling all new data from CloudKit, but maybe I'm not understanding that calling a completion handler doubles the values and maybe I need to removeAll inside of that? I'm just really not sure
Does anyone have anything they see I'm doing wrong, or anything they'd do to fix my code?
Thanks!
Might have to do with your async call to cloudkit. I'm not too familiar with refresh control but here is a way to maybe solve your problem and also make your code a little cleaner.
func getData(_ completion: () -> ()) {
teamColorArray.removeAll()
cloud.getCloudKit { [weak self] (game: [Game]) in
guard let unwrappedSelf = self else { return }
var updatedColorArray = [String]()
game.forEach { updatedColorArray.append($0.teamColor) }
unwrappedSelf.teamColorArray = updatedColorArray
completion()
}
}
now when you call getData it would look like this
getData {
DispatchQueue.main.async { [weak self] in
self?.tableView.reloadData()
self?.refreshControl?.endRefreshing()
}
}
you add weak self to remove the possibility of retain cycles
make sure your updating UI from the main thread
Call reloadData and endRefreshing when you know the array has been set properly
I put teamColorArray.removeAll() inside the getData function since it seems like you will need to call it everytime and it saves you from having to add it before the function everytime.
I have a Button on First VC which is directed to two active states.
1) SecondVC
override func viewDidLoad() {
super.viewDidLoad()
subjectPickerView.dataSource = self
subjectPickerView.delegate = self
SwiftyRequest()
// Used the text from the First View Controller to set the label
}
func SwiftyRequest(){
print("SecondViewController METHOD BEGINS")
let jsonobj = UserDefaults.standard.object(forKey: "PostData")
let json = JSON(jsonobj as Any)
for i in 0 ..< json.count{
let arrayValue = json[i]["name"].stringValue
print(arrayValue)
self.subjects.append(arrayValue)
self.subjectPickerView.reloadAllComponents()
}
print(self.subjects)
}
2) IBAction of FirstVC
#IBAction func buttonPressed(_ sender: Any) {
Alamofire.request("http://localhost/AIT/attempt3.php",method: .post, parameters: ["something": semValue, "branch" : streamValue])
.responseJSON { response in
print(response.result)
if let JSON1 = response.result.value {
print("Did receive JSON data: \(JSON1)")
// JSONData.someData = JSON1 as AnyObject?
UserDefaults.standard.set(JSON1, forKey: "PostData")
UserDefaults.standard.synchronize()
}
else {
print("JSON data is nil.")
}
}
}
NOW, Whenever i pressed the button it calls the viewDidLoad of SecondVC before IBAction of FirstVC which is a bit problematic for my app! How can i decide the priority between these two function.
You have to think about what you want to happen. Clearly the Alamofire call is going to take some time. What do you want to do with the 2nd VC while that time elapses? What do you want to do if the call does not return at all?
This is a common problem when dependent on external resources. How do you manage the UI? Do you present the UI in a partial state? Do you put a popover saying something like "loading". Or do you wait for the resource to complete before presenting the 2nd VC at all?
We cannot make that decision for you, since it depends on your requirement. There are ways to implement each one, though. If the resource usually responds quickly you could show the VC in a partial state and then populate it on some kind of callback. Typically call backs are either (1) blocks (2) delegate methods or (3) notifications. There is also (less commonly) (4) KVO. You should probably research the pros and cons of each.