Setting images in UITableViewCell in Swift - ios

Question

I have a list of reddit posts that I want to display the thumbnail of, if it exists. I have it functioning, but it's very buggy. There are 2 main issues:
Images resize on tap
Images shuffle on scroll
This is the code:
override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCellWithIdentifier("Post", forIndexPath: indexPath) as UITableViewCell
let post = swarm.posts[indexPath.row]
cell.textLabel!.text = post.title
if(post.thumb? != nil && post.thumb! != "self") {
cell.imageView!.image = UIImage(named: "first.imageset")
var image = self.imageCache[post.thumb!]
if(image == nil) {
FetchAsync(url: post.thumb!) { data in // code is at bottom, this just drys things up
if(data? != nil) {
image = UIImage(data: data!)
self.imageCache[post.thumb!] = image
dispatch_async(dispatch_get_main_queue(), {
if let originalCell = tableView.cellForRowAtIndexPath(indexPath) {
originalCell.imageView?.image = image
originalCell.imageView?.frame = CGRectMake(5,5,35,35)
}
})
}
}
} else {
dispatch_async(dispatch_get_main_queue(), {
if let originalCell = tableView.cellForRowAtIndexPath(indexPath) {
originalCell.imageView?.image = image
originalCell.imageView?.frame = CGRectMake(5,5,35,35)
}
})
}
}
return cell
}
This is the app when it loads up - looks like everything is working:
Then if I tap on an image (even when you scroll) it resizes:
And if you scroll up and down, the pictures get all screwy (look at the middle post - Generics fun):
What am I doing wrong?
** Pictures and Titles are pulled from reddit, not generated by me **
EDIT: FetchAsync class as promised:
class FetchAsync {
var url: String
var callback: (NSData?) -> ()
init(url: String, callback: (NSData?) -> ()) {
self.url = url
self.callback = callback
self.fetch()
}
func fetch() {
var imageRequest: NSURLRequest = NSURLRequest(URL: NSURL(string: self.url)!)
NSURLConnection.sendAsynchronousRequest(imageRequest,
queue: NSOperationQueue.mainQueue(),
completionHandler: { response, data, error in
if(error == nil) {
self.callback(data)
} else {
self.callback(nil)
}
})
callback(nil)
}
}

Answer 1

Unfortunately, this seems to be a limitation of the "Basic" table view cell. What I ended up doing was creating a custom TableViewCell. A relied on a tutorial by Ray Wenderlich that can be found here: http://www.raywenderlich.com/68112/video-tutorial-table-views-custom-cells
It's a bit of a bummer since the code is so trivial, but I guess on the bright side that means it's a 'simple' solution.
My final code:
PostCell.swift (all scaffolded code)
import UIKit
class PostCell: UITableViewCell {
#IBOutlet weak var thumb: UIImageView!
#IBOutlet weak var title: UILabel!
override func awakeFromNib() {
super.awakeFromNib()
// Initialization code
}
override func setSelected(selected: Bool, animated: Bool) {
super.setSelected(selected, animated: animated)
// Configure the view for the selected state
}
}
PostsController.swift
override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCellWithIdentifier("PostCell", forIndexPath: indexPath) as PostCell
let post = swarm.posts[indexPath.row]
cell.title!.text = post.title
if(post.thumb? != nil && post.thumb! != "self") {
cell.thumb!.image = UIImage(named: "first.imageset")
cell.thumb!.contentMode = .ScaleAspectFit
var image = self.imageCache[post.thumb!]
if(image == nil) {
FetchAsync(url: post.thumb!) { data in
if(data? != nil) {
image = UIImage(data: data!)
self.imageCache[post.thumb!] = image
dispatch_async(dispatch_get_main_queue(), {
if let postCell = tableView.cellForRowAtIndexPath(indexPath) as? PostCell {
postCell.thumb!.image = image
}
})
}
}
} else {
dispatch_async(dispatch_get_main_queue(), {
if let postCell = tableView.cellForRowAtIndexPath(indexPath) as? PostCell {
postCell.thumb!.image = image
}
})
}
}
return cell
}
And my measly storyboard:

Answer 2

I'm not sure the best way to do this, but here a couple of solutions:
Use AFNetworking, like everyone else does. It has the idea of a place holder image, async downloading of the replacement image, and smart caching. Install using cocoa pods, make a bridging file with #import "UIImageView+AFNetworking.h"
Create two different types of cells. Before grabbing a cell with dequeReusableCell... in your cellForRowAtIndexPath, check if it's expanded. If expanded, return and populate an expanded cell otherwise return and populated an unexpanded cell. The cell is usually expanded if it is the 'selected' cell.
Your mileage may vary

Answer 3

it is a huge mistake to call tableView.cellForRowAtIndexPath from within UITableViewDataSource's implementation of tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell. Instead when the async fetch of the thumb image is completed, update your model with the image, then request tableView to reloadRows for that specific cell's indexPath. Let your data source determine the correct indexPath. If the cell is offscreen by the time the image download is complete there will be no performance impact. And of course reloadRows on the main thread.