Autolayout images inside cells in tableview. Correct layout but only once scrolling down and back up? - swift

Question

Im trying to get tableview cells with auto resizing images to work. Basically I want the image width in the cell to always be the same, and the height to change in accordance with the aspect ratio of the image.
I have created a cell class, which only has outlets for a label, imageView and a NSLayoutConstraint for the height of the image. I have some async methods to download an image and set it as the image for the cell imageView. Then the completion handle gets called and I run the following code to adjust the height constraint to the correct height:
cell.cellPhoto.loadImageFromURL(url: photos[indexPath.row].thumbnailURL, completion: {
// Set imageView height to the width
let imageSize = cell.cellPhoto.image?.size
let maxHeight = ((self.tableView.frame.width-30.0)*imageSize!.height) / imageSize!.width
cell.cellPhotoHeight.constant = maxHeight
cell.layoutIfNeeded()
})
return cell
And here is the UIImageView extension I wrote which loads images:
func loadImageFromURL(url: String, completion: #escaping () -> Void) {
let url = URL(string: url)
makeDataRequest(url: url!, completion: { data in
DispatchQueue.main.async {
self.image = UIImage(data: data!)
completion()
}
})
}
And the makeDataRequest function which it calls:
func makeDataRequest(url: URL, completion: #escaping (Data?) -> Void) {
let session = URLSession.shared
let task = session.dataTask(with: url, completionHandler: { data, response, error in
if error == nil {
let response = response as? HTTPURLResponse
switch response?.statusCode {
case 200:
completion(data)
case 404:
print("Invalid URL for request")
default:
print("Something else went wrong in the data request")
}
} else {
print(error?.localizedDescription ?? "Error")
}
})
task.resume()
}
This works for all the cells out of frame, but the imageviews in the cells in the frame are small. Only when I scroll down and then back up again do they correctly size. How do I fix this? I know other people have had this issue but trying their fixes did nothing.

Answer 1

I had to sorta recreate the problem to understand what was going on. Basically you need to reload the tableview. I would do this when a picture finishes downloading.
In the view controller that has the table view var. Add this to the viewDidLoad() function.
override func viewDidLoad() {
super.viewDidLoad()
tableView.delegate = self
tableView.dataSource = self
//Create a notification so we can update the list from anywhere in the app. Good if you are calling this from an other class.
NotificationCenter.default.addObserver(self, selector: #selector(loadList), name: NSNotification.Name(rawValue: "loadList"), object: nil)
}
//This function updates the cells in the table view
#objc func loadList(){
//load data here
self.tableView.reloadData()
}
Now, when the photo is done downloading, you can notify the viewcontroller to reload the table view by using the following,
func loadImageFromURL(url: String, completion: #escaping () -> Void) {
let url = URL(string: url)
makeDataRequest(url: url!, completion: { data in
DispatchQueue.main.async {
self.image = UIImage(data: data!)
completion()
//This isn't the best way to do this as, if you have 25+ pictures,
//the list will pretty much freeze up every time the list has to be reloaded.
//What you could do is have a flag to check if the first 'n' number of cells
//have been loaded, and if so then don't reload the tableview.
//Basically what I'm saying is, if the cells are off the screen who cares.
NotificationCenter.default.post(name: NSNotification.Name(rawValue: "loadList"), object: nil)
}
})
}
Heres something I did to have better Async, see below.
My code as follows, I didn't do the resizing ratio thing like you did but the same idea applies. It's how you go about reloading the table view. Also, I personally don't like writing my own download code, with status code and everything. It isn't fun, why reinvent the wheel when someone else has done it?
Podfile
pod 'SDWebImage', '~> 5.0'
mCell.swift
class mCell: UITableViewCell {
//This keeps track to see if the cell has been already resized. This is only needed once.
var flag = false
#IBOutlet weak var cellLabel: UILabel!
#IBOutlet weak var cell_IV: UIImageView!
override func awakeFromNib() { super.awakeFromNib() }
}
viewController.swift (Click to see full code)
I'm just going to give the highlights of the code here.
//Set the image based on a url
//Remember this is all done with Async...In the backgorund, on a custom thread.
mCell.cell_IV.sd_setImage(with: URL(string: ViewController.cell_pic_url[row])) { (image, error, cache, urls) in
// If failed to load image
if (error != nil) {
//Set to defult
mCell.cell_IV.image = UIImage(named: "redx.png")
}
//Else we got the image from the web.
else {
//Set the cell image to the one we downloaded
mCell.cell_IV.image = image
//This is a flag to reload the tableview once the image is done downloading. I set a var in the cell class, this is to make sure the this is ONLY CALLED once. Otherwise the app will get stuck in an infinite loop.
if (mCell.flag != true){
DispatchQueue.main.asyncAfter(deadline: .now() + 0.025){ //Nothing wrong with a little lag.
NotificationCenter.default.post(name: NSNotification.Name(rawValue: "loadList"), object: nil)
mCell.flag = true
}
}
}
}