问题
I am using this code to display image in to my customCell. This is my code to fetch image from API. It was working fine as per the given link. But the problem started when I added this code to my cellForItemAt indexPath: for image Cache.
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
// Displaying other elements with text
customCell.mainImage.image = nil
var image1 = self.imageCache.object(forKey: indexPath.item as AnyObject) as? UIImage
if (image1 == nil) {
self.ImageFetcher(postId: self.myArray[indexPath.item].id!, completion: { (image) in
image1 = image
self.imageCache.setObject(image1!, forKey: indexPath.item as AnyObject)
})
}
DispatchQueue.main.async {
customCell.mainImage.image = image1
}
}
Above code works fine without any error but, not displaying/loading images until I scroll the collectionView up and down. Don't understand what I am missing here. Any help would be appreciated !!
回答1:
Please try this,
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
// Displaying other elements with text
if let image1 = self.imageCache.object(forKey: indexPath.item as AnyObject) as? UIImage
{
customCell.mainImage.image = image1
}
else {
self.ImageFetcher(postId: self.myArray[indexPath.item].id!, completion: { (image) in
self.imageCache.setObject(image, forKey: indexPath.item as AnyObject)
customCell.mainImage.image = image1
})
}
}
回答2:
STEP:1 Create extension of uiimageview to download image from url, and if already downloaded then from cache
let imageCache = NSCache()
extension UIImageView {
func loadImageUsingCacheWithURLString(url: NSURL) {
self.image = nil
// First check if there is an image in the cache
if let cachedImage = imageCache.objectForKey(url) as? UIImage {
self.image = cachedImage
return
}
else {
// Otherwise download image using the url location in Google Firebase
NSURLSession.sharedSession().dataTaskWithURL(url, completionHandler: { (data, response, error) in
if error != nil {
print(error)
}
else {
dispatch_async(dispatch_get_main_queue(), {
// Cache to image so it doesn't need to be reloaded every time the user scrolls and table cells are re-used.
if let downloadedImage = UIImage(data: data!) {
imageCache.setObject(downloadedImage, forKey: url)
self.image = downloadedImage
}
})
}
}).resume()
}
}
STEP 2 : Usage
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
// Displaying other elements with text
customCell.mainImage.loadImageUsingCacheWithURLString(url: yoururl)
}
来源：https://stackoverflow.com/questions/45465737/collectionviewcell-image-doesnt-display-until-scrolling