I am passing a String (postID) between two view controllers (respectively DiscoverVC and DetailVC) using the sender parameter of the method performSegue.
When the destination VC is presented, I can actually see that the String I passed is correctly assigned to a local variable “postID” (since I can print it). But when I try to perform some operations on it, such as querying in the Firebase Database, it seems like the String is no longer present. I don’t know how to solve this problem even though it seems stupid to solve.
This is the code of the viewDidLoad() method of the destinationVC
var postID = “”
override func viewDidLoad() {
print("this is the postID that I get from previous VC \(postID)")
super.viewDidLoad()
updateViewDetail()
}
This is the method updateViewDetail() which makes some operations with the Firebase database. It is trying to retrieve the post using the PostID String.
func updateViewDetail(){
Api.Post.observePost(with: postID) { (post) in
print("post id inside \(post.id)")
guard let postUid = post.uid else{
return
}
self.fetchUsers(uid: postUid) {
self.post = post
self.tableView.reloadData()
}
}
}
When I try to print the post.id inside the closure it is nil. Do you know how I can solve this problem?
Just for the sake of completion, this is the code of the observePost method that retrieves the post object from the FIRDatabase:
func observePost(with id : String, completion: #escaping (Post)-> Void) {
REF_Posts.child(id).observeSingleEvent(of: .value) { (snaphsot) in
if let dict = snaphsot.value as? [String : Any]{
let post = Post.transformPost(dict: dict, key: snaphsot.key)
completion(post)
}
}
}
EDIT 1:
This is the code of prepare method set in the previous VC :
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
let detailVC = segue.destination as! DetailViewController
let postid = sender as! String
detailVC.postID = postid
}
Related
I'm new in iOS.
I'm trying to pass my array data to another view controller through prepareforsegue method.
And this api is called inside the #IBAction func ButtonTapped( ).
class FirstVc {
var location = [Any]()
self.clientrequest.request(url: "http://api.details.in/api/users/alllocation", method: .GET, completion: {
res , err in
let json = try! JSONSerialization.data(withJSONObject: res , options: .prettyPrinted)
let decode = try! JSONDecoder().decode(SelectLocation.self, from:json)
self.location = decode.states
//I'm getting all locations here
print(self.location)
})
}
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if segue.destination is SecondVc
{
let vc = segue.destination as? SecondVc
//here I'm assigning the variable and while I'm printing location here then also I'm getting the value
vc?.mineSpillere2 = self.location
}
}
class SecondVc{
#IBOutlet weak var selectState: UILabel!
var mineSpillere2 = [Any]()
override func viewDidLoad() {
//While I'm trying to print mineSpillere2 here I', getting []
selectState.text = mineSpillere2 as? String
}
}
One problem might be that you don't actually assign the variable (because vc may be nil). Also you may want to use segueIdentifiers, especially if you have more than one. To make sure that you do so, you may want to use something like this:
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if let vc = segue.destination as? SecondVc //, segue.identifier = "YOUR_SEGUE_ID"
{
vc.mineSpillere2 = self.location
} else { print("SecondVc couldn't be initialised!") }
}
First, the problem is that web service request is not executed asynchronously but synchronously. In other words, your segue is already performed before decode.states is assigned to the location variable.
The solution is to call performSegue function in the completion block:
self.clientrequest.request(url: "http://api.details.in/api/users/alllocation", method: .GET, completion: {
res , err in
let json = try! JSONSerialization.data(withJSONObject: res , options: .prettyPrinted)
let decode = try! JSONDecoder().decode(SelectLocation.self, from:json)
self.location = decode.states
self.performSegue(identifier: "your identifier",
sender: nil)
//I'm getting all locations here
print(self.location)
})
Second,
Make sure your segue is assigned from VC1 to VC2 not Button to VC2.
There are several way to pass this in another ViewController. Good way is make a model class and pass model object to another vc .
Or might be another short and easy solution is make Global variable. So you can access it from any ViewController class. like
var myGloblArray= [Any]()
//add your result array in this array , you can access it from second VC Directly.
class FirstVc {
...
}
I am new to IOS programming and don't really know what I'm asking but I will try and explain
I am using Firebase to auth and then I want to take the UID and pass it to a different VC the problem I am getting I cant get the var userID to print out side of the IBAction here is where I am so far, any pointer would get good cheers guys
#IBAction func creatAccountPressed(_ sender: Any) {
if let email = emailTextField.text,
let password = passwordTextField.text,
let name = nameTextField.text {
Auth.auth().createUser(withEmail: email, password: password, completion: { user, error in
if let firebaseError = error {
print(firebaseError.localizedDescription)
}
let userID = user!.uid
let userEmail: String = self.emailTextField.text!
let fullName: String = self.nameTextField.text!
self.ref.child("users").child(userID).setValue(["Email": userEmail, "Name": fullName])
self.userID1 = user!.uid as! String
})
print(self.userID1)
presentLoggedInScreen()
}
}
func presentLoggedInScreen() {
let stroyboard: UIStoryboard = UIStoryboard(name: "Main", bundle: nil)
let loggedInVC: LoggedInVCViewController = stroyboard.instantiateViewController(withIdentifier: "loggedInVC") as! LoggedInVCViewController
self.present(loggedInVC, animated: true, completion: nil)
}
One the simpler way to pass info from one VC to another is either through an initiliazer, or through a variable that you set before presenting the second VC.
Since you are new to this, try the variable approach for now, so if say, you're passing a string:
class LoggedInVCViewController : UIViewController {
var info : String? {
didSet {
if let newInfo = self.info {
//do what ever you need to do here
}
}
}
override viewDidLoad() {
super.viewDidLoad()
}
}
func presentLoggedInScreen(yourInfo: String) {
let stroyboard:UIStoryboard = UIStoryboard(name: "Main", bundle: nil)
let loggedInVC:LoggedInVCViewController =
storyboard.instantiateViewController(withIdentifier: "loggedInVC") as!
LoggedInVCViewController
loggedInVC.info = yourInfo
self.present(loggedInVC, animated: true, completion: nil)
}
Mind you, you can always use any other king of variable Class for info. You also would program your VC to execute some methods inside of the get bracket of the property, populate some fields based on the content of info, load a specific UI etc.
Another usefull way is to go the initialization route, but unfortunately you cannot use it with Storyboard nibs (sad i know, but this post goes over this nicely), but it still usefull whenever you will feel comfortable enough to initialize and design VC's programmatically (which I would learn ASAP if were you).
You pass a variable in a custom intializer method for your VC:
class LoggedInVCViewController : UIViewController {
var info : Any? {
get {
if let this = self.info {
return this
} else {
return nil
}
} set {
if let new = newValue {
//
}
}
}
init(info: Any?) {
//This first line is key, it also calls viewDidLoad() internally, so don't re-write viewDidLoad() here!!
super.init(nibName: nil, bundle: nil)
if let newInfo = info {
//here we check info for whatever you pass to it
self.info = newInfo
}
}
override func viewDidLoad() {
super.viewDidLoad()
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
}
So you would use is as:
func presentLoggedInScreen(yourInfo: String) {
let loggedInVC = LoggedInVCViewController(info: yourInfo)
self.present(loggedInVC, animated: true, completion: nil)
}
Obviously, as stated, this method cannot be used with Storyboards, but very usefull and, as I'm sure you can see, is much more compact.
I suggest you get familiar with Swift Properties of the docs, along with some blog tips such as this one. You can get pretty creative after a while.
For learning more programmatic approaches, i strongly recommend this YouTube channel: Let's Build That App, I personnaly haven't found a better reference point for programmatic approach Swift programming.
Don't hesitate to ask questions!
UPDATE
Your IBAction should look like this:
#IBAction func creatAccountPressed(_ sender: Any) {
if let email = emailTextField.text, let password = passwordTextField.text, let name = nameTextField.text {
Auth.auth().createUser(withEmail: email, password: password, completion: { user, error in
if let firebaseError = error {
print(firebaseError.localizedDescription)
}
let userID = user!.uid
let userEmail: String = self.emailTextField.text!
let fullName: String = self.nameTextField.text!
self.ref.child("users").child(userID).setValue(["Email": userEmail, "Name": fullName])
self.userID1 = user!.uid as! String
print(self.userID1)
presentLoggedInScreen(yourInfo: self.userID1)
})
}
}
Put
print(self.userID1)
presentLoggedInScreen()
inside the completion block. Currently those lines are almost certain to happen before the completion block is done as the block is executed after the required network calls return.
Be sure to wrap presentLoggedInScreen() in a block that dispatches it to the main thread as it touches the UI and all UI calls must be made from the main thread.
DispatchQueue.main.async {
presentLoggedInScreen()
}
This will make it so that presentLoggedInScreen() executes after the value as been assigned to userID1 allowing you to pass the value over to the incoming view controller (assuming, of course, that the incoming VC has an appropriate variable to pass userID1 into).
Something like:
loggedInVC.userID = self.userID1
before you present the VC.
I am trying to take facebook values, such as name and email, and transferring them to another view controller where they populate their corresponding text fields. However, when I try to populate the text fields with this code
let fbEmail = data["email"]
let fbName = data["name"]
func prepare(for segue: UIStoryboardSegue, sender: Any?) {
let vc = segue.destination as? CreateAccountVC
vc!.emailTxt = self.fbName
vc!.fullnameTxt = self.fbEmail
}
I receive an error saying "Cannot assign type String to type UITextField!" I'm confused here as I thought that text fields only take strings (I'm very new to coding/programming).
So basically, how do I get these values gathered in one view controller to populate text fields in another view controller? Any help would be greatly appreciated! Thanks!
Error reason is you need to assign it to the UITextField's text property.
You can also use variables to set them. And set textfield's values in your CreateAccountVC controller's viewDidLoad function. Like this:
Your first controller where you take facebook values:
let fbEmail = data["email"]
let fbName = data["name"]
func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if let vc = segue.destination as? CreateAccountVC {
vc.emailTxtValue = self.fbName
vc.fullnameTxtValue = self.fbEmail
}
}
Your CreateAccountVC :
class CreateAccountVC: UIViewController {
var emailTxtValue:String?
var fullnameTxtValue:String?
override func viewDidLoad() {
super.viewDidLoad()
emailTxt.text = emailTxtValue
fullnameTxt.text = fullnameTxtValue
}
}
I have a MapViewController with a prepareForSegue(_:sender:)method, which I intend to use to send data to LandmarkTableViewController, and is called when a button is pressed.
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
let destinationvc = segue.destinationViewController
if let landmarkvc = destinationvc as? LandmarkTableViewController {
if let identifier = segue.identifier {
let library = Landmark(name: "Run Run Shaw Library", properties: ["Chinese Kanji", "Gray", "Green Plants"])
let bank = Landmark(name: "Hang Seng Bank", properties: ["Chinese Kanji", "Green"])
switch identifier {
case "showLibrary" : landmarkvc.passedLandmark = library // pass data to LandmarkTableViewController
case "showBank" : landmarkvc.passedLandmark = bank // pass data to LandmarkTableViewController
default : break
}
}
}
}
The LandmarkTableViewController is properly set up to display the String array properties, with one String on each row. So what I intend to do is pass the appropriate data for the table to properties according to which button was pressed, and let LandmarkTableViewController display the corresponding properties.
class LandmarkTableViewController: UITableViewController {
var properties = [String]()
var passedLandmark = Landmark(name: "temp", properties: ["temp"]) // initially set to default value
override func viewDidLoad() {
super.viewDidLoad()
loadSampleProperties()
}
func loadSampleProperties() {
self.properties = passedLandmark!.properties
}
// other methods....
}
class Landmark {
var name: String
var properties: [String]
init?(name: String, properties: [String]) {
self.name = name
self.properties = properties
// Initialization should fail if there is no name or if there is no property.
if name.isEmpty || properties.isEmpty {
return nil
}
}
However, when I run the code, only temp is displayed in the table view. I've been stuck on this for a long time now, so any help is much appreciated!
Edit: loadData() inside of viewDidLoad() is changed to the correct loadSampleProperties(). I made an error while posting the code to the question.
I think this should solve your problem if not double check your identifiers
and you can make sure to data passing with adding print(passedLandmark) to viewDidLoad() or breakpoint to make sure you getting the data
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
let destinationvc = segue.destinationViewController
if let landmarkvc = destinationvc as? LandmarkTableViewController {
if segue.identifier == "showLibrary" {
let library = Landmark(name: "Run Run Shaw Library", properties: ["Chinese Kanji", "Gray", "Green Plants"])
landmarkvc.passedLandmark = library
}
if segue.identifier == "showBank" {
let bank = Landmark(name: "Hang Seng Bank", properties: ["Chinese Kanji", "Green"])
landmarkvc.passedLandmark = bank
}
}
}
Hope this will helps
Code is missing from your quote, so I can't be sure, but I assume your loadData() method is the one that reloads the table view data with Landmark you've passed in prepareForSegue. If that is the case:
viewDidLoad() is called before prepareForSegue, so that all the views and elements of the destinationViewController are loaded and ready to use. Thus, in your case, the table view is loaded with your "temp" data and nothing makes it reload when you set the proper one.
You have two options:
You could call loadData()/reloadData() in viewWillAppear for example, which is called after prepareForSegue(). Bare in mind that viewWillAppear will possibly be called again in some other navigation.
Otherwise, you could instantiate and present/push the new controller in your parent view controller, instead of using the segue.
I have a push segue on my StoryBoard which is named toGuestVC.
I use that to segue to the next ViewController in my didSelectRowAtIndexPath method like so:
override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
let username = followUsernameArray[indexPath.row]
performSegue(withIdentifier: SG_TO_GUEST_VIEW_CONTROLLER, sender: username)
}
Then in my prepareForSegue:
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if segue.identifier == SG_TO_GUEST_VIEW_CONTROLLER {
if let nextVC = segue.destination as? GuestCollectionVC, let sender = sender as? String {
print("PRINTING NEXT VC: \(nextVC)") //This prints out the memory address. Not sure if this is what you meant by print nextVC.
nextVC.guestUser = sender
}
}
}
For some reason this line in my prepareForSegue is not running:
nextVC.guestUser = sender.username
When I try to print out the value guestUser in my nextViewController the value of guestUser is nil. But when I print out the value of sender in my prepareForSegue method it is not nil.
So is my sender value not being passed to the next ViewController? I can't find a solution to this problem any ideas?
GuestCollectionVC Implementation:
import UIKit
import Parse
private let reuseIdentifier = "Cell"
class GuestCollectionVC: UICollectionViewController {
var guestUser: String!
override func viewDidLoad() {
super.viewDidLoad()
print("PRINTING SELF IN GuestCollectionVC: \(self)")
loadPosts()
}
func loadPosts() {
//Load posts query
let query = PFQuery(className: PF_POSTS_CLASS)
query.limit = postCount
//Getting error here below this comment when I use guestUser since it is nil
query.whereKey(PF_POSTS_USERNAME_COLUMN, equalTo: guestUser)
query.findObjectsInBackground { (result: [PFObject]?, error: Error?) -> Void in
if error == nil {
if let result = result {
self.uuidOfPosts.removeAll(keepingCapacity: false)
self.imageArrayOfPFFIle.removeAll(keepingCapacity: false)
for postObject in result {
if let uuid = postObject[PF_POSTS_UUID_COLUMN] as? String, let pic = postObject[PF_POSTS_PIC_COLUMN] as? PFFile {
self.uuidOfPosts.append(uuid)
self.imageArrayOfPFFIle.append(pic)
}
}
self.collectionView?.reloadData()
}
}else if error != nil {
print("ERROR FROM GUEST COLLECTION VC FROM loadPosts FUNCTION: \(error?.localizedDescription)")
}
}
}
}
So this is my implementation in the GuestViewController. In my loadPosts method where I used the variable guestUser I am getting the error:
fatal error: unexpectedly found nil while unwrapping an Optional value
From console printing
PRINTING NEXT VC: "InstagramClone.GuestCollectionVC: 0x7a6c5cc0"
PRINTING SELF IN GuestCollectionVC: "InstagramClone.GuestCollectionVC: 0x7a6c5100"
it's now obvious that hidden unexpected instance of GuestCollectionVC was created. So, there are different errors occurs depending on order of this two objects invoke their viewDidLoad method (can be any order). Also there are can be other errors in nextVC viewDidLoad method, but this is other story for other question.
You got this problems because you created action segue, that works automatically on cell click (hidden view controller created), and at the same time you are perform this segue in code, creating second controller nextVC.
To solve issue, you should find and remove that segue and add new one, not action segue from some element of your view controller, but "empty" segue between view controllers. To create segue of this type you should select first view controller, hold "control" key and start dragging to next view controller from yellow square on top of first view controller (that symbol controller itself), choose "show", and set identifier.
Since I don't have the full context of the values within your tableView method I can only speculate. That said, the sender you're passing in should be the view controller:
performSegue(withIdentifier: "toGuestVC", sender: username)
You're passing in a value called username which looks to be a string value? It should be something like:
performSegue(withIdentifier: "toGuestVC", sender: self)
where self is your view controller. If you're passing in a string value to sender then in your prepareForSegue method then sender does not have a property called username sender actually is username. Therefore you should pass the value elsewhere:
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
let indexPath = self.tableView.indexPathForSelectedRow
if let nextVC = segue.destination as? GuestCollectionVC {
nextVC.guestUser = followUsernameArray[indexPath.row]
}
}