Asynchronously Loading Image constantly causes image to flicker? - ios

Question

I have a header view for every UITableViewCell. In this header view, I load a picture of an individual via an asynchronous function in the Facebook API. However, because the function is asynchronous, I believe the function is called multiple times over and over again, causing the image to flicker constantly. I would imagine a fix to this issue would be to load the images in viewDidLoad in an array first, then display the array contents in the header view of the UITableViewCell. However, I am having trouble implementing this because of the asynchronous nature of the function: I can't seem to grab every photo, and then continue on with my program. Here is my attempt:
//Function to get a user's profile picture
func getProfilePicture(completion: (result: Bool, image: UIImage?) -> Void){
// Get user profile pic
let url = NSURL(string: "https://graph.facebook.com/1234567890/picture?type=large")
let urlRequest = NSURLRequest(URL: url!)
//Asynchronous request to display image
NSURLConnection.sendAsynchronousRequest(urlRequest, queue: NSOperationQueue.mainQueue()) { (response:NSURLResponse!, data:NSData!, error:NSError!) -> Void in
if error != nil{
println("Error: \(error)")
}
// Display the image
let image = UIImage(data: data)
if(image != nil){
completion(result: true, image: image)
}
}
}
override func viewDidLoad() {
self.getProfilePicture { (result, image) -> Void in
if(result == true){
println("Loading Photo")
self.creatorImages.append(image!)
}
else{
println("False")
}
}
}
func tableView(tableView: UITableView, viewForHeaderInSection section: Int) -> UIView? {
//Show section header cell with image
var cellIdentifier = "SectionHeaderCell"
var headerView = tableView.dequeueReusableCellWithIdentifier(cellIdentifier) as! SectionHeaderCell
headerView.headerImage.image = self.creatorImages[section]
headerView.headerImage.clipsToBounds = true
headerView.headerImage.layer.cornerRadius = headerView.headerImage.frame.size.width / 2
return headerView
}
As seen by the program above, I the global array that I created called self.creatorImages which holds the array of images I grab from the Facebook API is always empty and I need to "wait" for all the pictures to populate the array before actually using it. I'm not sure how to accomplish this because I did try a completion handler in my getProfilePicture function but that didn't seem to help and that is one way I have learned to deal with asynchronous functions. Any other ideas? Thanks!

Answer 1

I had the same problem but mine was in Objective-C
Well, the structure is not that different, what i did was adding condition with:
headerView.headerImage.image
Here's an improved solution that i think suits your implementation..
since you placed self.getProfilePicture inside viewDidLoad it will only be called once section==0 will only contain an image,
the code below will request for addition image if self.creatorImages's index is out of range/bounds
func tableView(tableView: UITableView, viewForHeaderInSection section: Int) -> UIView? {
//Show section header cell with image
var cellIdentifier = "SectionHeaderCell"
var headerView = tableView.dequeueReusableCellWithIdentifier(cellIdentifier) as! SectionHeaderCell
if (section < self.creatorImages.count) // validate self.creatorImages index to prevent 'Array index out of range' error
{
if (headerView.headerImage.image == nil) // prevents the blinks
{
headerView.headerImage.image = self.creatorImages[section];
}
}
else // requests for additional image at section
{
// this will be called more than expected because of tableView.reloadData()
println("Loading Photo")
self.getProfilePicture { (result, image) -> Void in
if(result == true) {
//simply appending will do the work but i suggest something like:
if (self.creatorImages.count <= section)
{
self.creatorImages.append(image!)
tableView.reloadData()
println("self.creatorImages.count \(self.creatorImages.count)")
}
//that will prevent appending excessively to data source
}
else{
println("Error loading image")
}
}
}
headerView.headerImage.clipsToBounds = true
headerView.headerImage.layer.cornerRadius = headerView.headerImage.frame.size.width / 2
return headerView
}
You sure have different implementation from what i have in mind, but codes in edit history is not in vain, right?.. hahahaha.. ;)
Hope i've helped you.. Cheers!