Why tableview didn't show the correct image? - ios

Question

I have two Viewcontroller A and B. A will download all the photo in collectionview then I can click on single cell to go to Viewcontroller B which is the tableview to show only this single image that passed from A.
But its working fine when first lunch the app but once I add new photo in the collectionview then I clicked this new photo to go to Viewcontroller B but B didn't show the correct photo showing some other photo. I print out the photo data postImg in viewcronller A and B the data is the same but B is not showing the correct photo. Why? When I rebuild the program it's working the issues seems only happened when I add new photo.
Here is code to load the pic from server
func loadPosts(){
let query = PFQuery(className: "posts")
query.whereKey("username", equalTo:PFUser.current()!.username!)
query.skip = self.picArray.count // skip the already loaded images
query.findObjectsInBackground { (objects, error) in
if error == nil {
if let objects = objects{
for object in objects{
self.collectionView?.performBatchUpdates({
let indexPath = IndexPath(row: self.uuidArray.count, section: 0)
self.uuidArray.append(object.value(forKey: "uuid") as! String)
self.picArray.append(object.value(forKey: "pic") as! PFFile)
self.collectionView?.insertItems(at: [indexPath])
}, completion: nil)
}
}
} else{
print(error!.localizedDescription)
}
}
}
Then var postImgData = [UIImage]() is the array used to save all the photos that downloaded from above function and this viable is defined at beginning of CLASS Viewcontroll A.
override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return picArray.count
}
override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
//define cell
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", for: indexPath) as! pictureCell
picArray[indexPath.row].getDataInBackground { (data, error) in
if error == nil {
cell.picImg.image = UIImage(data: data!)
self.postImgData.append(UIImage(data: data!)!)
} else {
print(error!.localizedDescription)
}
}
return cell
}
Then i click the cell to go to viewcontroller B . postImg is defined at beginning of Viewcontroller B as global viable to get the image date that you click on Viewcontroller A cell.
override func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
postImg = postImgData[indexPath.row]
let post = storyboard?.instantiateViewController(withIdentifier: "postVC") as! postVC
self.navigationController?.pushViewController(post, animated: true)
}
Then in Viewcotnroller B to show the photo
override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "Cell", for: indexPath) as! postCell
cell.picImg.image = postImg
return cell
}

Answer 1

First:
picArray[indexPath.row].getDataInBackground { (data, error) in
if error == nil {
cell.picImg.image = UIImage(data: data!)
self.postImgData.append(UIImage(data: data!)!) <== WHY do you append array?
} else {
print(error!.localizedDescription)
}
you should probably init array beforehand and set data like self.postImgData[indexPath.row] = UIImage(data: data!)!
That how we ensure correct order of images
2
override func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
let post = storyboard?.instantiateViewController(withIdentifier: "postVC") as! postVC
// Why dont use post.postImg = postImgData[indexPath.row]?
// Do not use Global vars, because you can change it from anywhere without noticing
self.navigationController?.pushViewController(post, animated: true)
}
So I suggest moving postImg var to controller B