Why my Collectionview cells are not showing when i move from that viewcontroller in swift? - json

Question

I am able to parse JSON and adding cells in Collectionview.. but if i move from this Viewcontroller and coming to viewcontroller then collectionview is not showing.. but added data in JSON
code for adding collectionview and JSON parsing:
class ImageItemModel{
var title: String?
var profileImage: UIImage?
var pic_id: Double?
init(title: String?, imgTitle: UIImage?, pic_id: Double?) {
self.title = title
self.profileImage = imgTitle
self.pic_id = pic_id
}
}
class EditProfileImageViewController: UIViewController {
#IBOutlet weak var titleTextfield: UITextField!
private var imageProfile : UIImage?
private var imagePicker : EasyImagePicker?
#IBOutlet weak var collectionView: UICollectionView!
var arrImageItems = [ImageItemModel]()
#IBAction func imgtitleSaveBtn(_ sender: Any) {
postServiceCall()
}
fileprivate func postServiceCall(){
if titleTextfield.text?.trim() == ""{
return self.view.makeToast("please add service title")
}
let parameters = ["image_title" : titleTextfield.text?.trim() ?? ""]
APIReqeustManager.sharedInstance.uploadMultipartFormData(param: parameters, url: CommonUrl.edit_profile_images, image: imageProfile, fileName: "image", vc: self, isHeaderNeeded: true) {(responseData) in
print("edit profile result \(responseData)")
if let result = responseData.dict?["result"] as? NSDictionary{
let success = result["status"] as? [String : Any]
let message = success?["message"] as? String
if message == "Success"{
let image = result["image"] as? [String : Any]
let picId = image?["id"]
self.arrImageItems.append(ImageItemModel(title: self.titleTextfield.text, imgTitle: self.imageProfile, pic_id: picId as! Double))
self.collectionView.reloadData()
}
else{
self.view.makeToast(CommonMessages.somethingWentWrong)
}
}
}
}
extension EditProfileImageViewController : UICollectionViewDelegate,UICollectionViewDataSource{
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return arrImageItems.count
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "ImageCollectionViewCell", for: indexPath) as! ImageCollectionViewCell
cell.imgView.image = arrImageItems[indexPath.item].profileImage
cell.lblTitle.text = arrImageItems[indexPath.row].title
cell.deleteButton.tag = indexPath.row
cell.deleteButton.addTarget(self, action: #selector(deleteService(sender:)), for: UIControl.Event.touchUpInside)
return cell
}
}
with the above code i am able to add collectionview cells and able to store data in JSON but.. if i move from this viewcontroller and coming back to this viewcontroller then collectionview is not showing, why? whats wrong? please do help me with code.. i got stuck here from long time.

Answer 1

There are couple of issues that you should fix for this to work properly. I will give you reason for each.-
You are loading your data with the postServiceCall() method which has an asynchronous network call. There is no way to know when the controller is done fetching the data to the arrImageItems array. So, you should have used a completion handler.
Now you are updating the collectionView within the asynchronous dataTask which a background thread. BIG mistake. Whenever you have any UI related task, you do it under the main thread. So, you could refactor the APIReqeustManager.sharedInstance.uploadMultipartFormData() part of your code following way-
APIReqeustManager.sharedInstance.uploadMultipartFormData(param: parameters, url: CommonUrl.edit_profile_images, image: imageProfile, fileName: "image", vc: self, isHeaderNeeded: true) {(responseData) in
print("edit profile result \(responseData)")
if let result = responseData.dict?["result"] as? NSDictionary{
let success = result["status"] as? [String : Any]
let message = success?["message"] as? String
if message == "Success"{
let image = result["image"] as? [String : Any]
let picId = image?["id"]
self.arrImageItems.append(ImageItemModel(title: self.titleTextfield.text, imgTitle: self.imageProfile, pic_id: picId as! Double))
DispatchQueue.main.async {
self.collectionView.reloadData()
}
}
else{
DispatchQueue.main.async {
self.view.makeToast(CommonMessages.somethingWentWrong)
}
}
}
}
Now unless you want your viewcontroller to show the data in your collectionView only when the action, imgtitleSaveBtn(_:) is triggered, you need to get data everytime, when your view controller appeared on screen. To fix that issue, you should get the data in the viewWillAppear(_:) method like-
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
postServiceCall()
}
Now, the above two edits should fix your issue depending on how you want to load your collectionview but your code is breaking quite some coding standards. Coding standards sounds like a clique but trust me you want to follow those if you ever want to update the capability of your app without breaking it. The following is just some hints-
Whenever you are in an asynchronous call, you should consider calling a completion handler for returning your data.
Should look into your methods, you are dangerously breaking the single responsibility principal.
In more than one place, you force unwrapped. Bad idea. You need your system to have a fail safe rather than just crashing on you.
Update 2:
Updates with a design pattern:
Compartmentalise your code in MVC pattern. Put the ImageItemModel class in its own file. See the image below to understand the design-
Customize the collectionViewCell within the ImageCollectionViewCell. Let's assume your custom cell has only the outlets.
class ImageCollectionViewCell: UICollectionViewCell {
#IBOutlet weak var imgView: UIImageView!
#IBOutlet weak var lblTitle: UILabel!
#IBOutlet weak var deleteButton: UIButton!{
didSet{
deleteButton.addTarget(self, action: #selector(deleteService(_:)), for: .touchUpInside)
}
}
// however this could easily be done with IBAction
#objc func deleteService(_ sender: UIButton){
}
}
Update the postServiceCall and return the data to your controller with a completion handler, means when the postServiceCall is done executing, an array of images or an empty array should be returned based on success or failure. Then the controller can decide what to do with the data, in your case update UI. with couple of refactoring, here is the updated controller code.
import UIKit
import EasyImagePicker
class EditProfileImageViewController: UIViewController {
#IBOutlet weak var collectionView: UICollectionView!{ //for troubleshooting
didSet{ //purpose, do it from code
collectionView.delegate = self
collectionView.dataSource = self
}
}
#IBOutlet weak var titleTextfield: UITextField!
private var imageProfile : UIImage?
private var imagePicker : EasyImagePicker? // you never used this var.
var arrImageItems = [ImageItemModel]()
// any time a view controller appears on screen this method gets called.
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
reloadMyCollectionView()
}
#IBAction func imgtitleSaveBtn(_ sender: Any) {
reloadMyCollectionView()
}
fileprivate func reloadMyCollectionView(){
postServiceCall{ images in
self.arrImageItems = images
DispatchQueue.main.async {
self.collectionView.reloadData()
}
}
}
// look into escaping closures to understand, why you need it here
fileprivate func postServiceCall(completed: #escaping(_ images: [ImageItemModel])->Void){
// don't force unwrap, get optional values safely with guard let
guard let titleText = titleTextfield.text, titleText == "" else{
return
}
let parameters = ["image_title" : titleText]
APIReqeustManager.sharedInstance.uploadMultipartFormData(param: parameters, url: CommonUrl.edit_profile_images, image: imageProfile, fileName: "image", vc: self, isHeaderNeeded: true) {(responseData) in
print("edit profile result \(responseData)")
//capture the data in local scope and return that array with a completion handler
var imageItems = []
if let result = responseData.dict?["result"] as? NSDictionary{
let success = result["status"] as? [String : Any]
let message = success?["message"] as? String
if message == "Success"{
let image = result["image"] as? [String : Any]
let picId = image?["id"]
imageItems.append(ImageItemModel(title: self.titleTextfield.text, imgTitle: self.imageProfile, pic_id: picId as! Double))
}
}
self.completed(imageItems) // if there is nothing in result,
//imageItems will be empty, otherwise it will have imageItemModel data
}
}
}
extension EditProfileImageViewController : UICollectionViewDelegate,UICollectionViewDataSource{
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return arrImageItems.count
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
if let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "ImageCollectionViewCell", for: indexPath) as? ImageCollectionViewCell{
cell.imgView.image = arrImageItems[indexPath.item].profileImage
cell.lblTitle.text = arrImageItems[indexPath.row].title
cell.deleteButton.tag = indexPath.row
//cell.deleteButton.addTarget(self, action: #selector(deleteService(sender:)), for: UIControl.Event.touchUpInside)
return cell
}
else{
return UICollectionViewCell()
}
}
}
Notice postServiceCall and cellForItemAt methods.
If you still have the same issue then you need to show your whole code to get any further help.