How to implement lazy loading of image without using SDImageCache? - objective-c

Question

How to implement lazy loading of image without using below link:
https://github.com/rs/SDWebImage
Note: I don't want to use any third party tool. I want to do from my side.

Answer 1

If you don't want to use any library (some are MIT or public domain licensed, so I think the only reason not to use them is that you want to learn how to build it yourself).
Here is how to do it with a simple and effective way:
1 : Put a temporary placeholder image in your imageView.
2 : Get your image in background thread.
2-a : If you want the cache feature, search for a cached image.
2-b : If no cache feature or no cached image, get your image from its source.
2-c : If cache feature, save the image to cache.
3 : In main thread show your image in the imageView.
Pseudo Code : (I wrote it on the go, it is not meant to run and it may have errors, sorry for that).
-(void) lazilyLoadImageFromURL :(NSURL *)url{
imageView.image = [UIImage imageNamed:#"Placeholder.png];
if([self cachedImageAvailableForURL:url){
imageView.image= [self cachedImageForURL:url];
}
else{
NSOperationQueue *queue = [NSOperationQueue mainQueue];
NSURLRequest *urlRequest = [NSURLRequest requestWithURL:url];
[NSURLConnection sendAsynchronousRequest:urlRequest queue:queue completionHandler:^(NSURLResponse * resp, NSData *data, NSError *error)
{
dispatch_async(dispatch_get_main_queue(),^
{
if ( error == nil && data )
{
UIImage *urlImage = [[UIImage alloc] initWithData:data];
imageView.image = urlImage;
[self saveImageInCache:image forURL:url];
}
});
}];
}
}
-(BOOL) cachedImageAvailableForURL:(NSURL*):url{
// check if there is a saved cached image for this url
}
-(UIImage *) cachedImageForURL:(NSURL*):url{
// returns the cached image for that url
}
-(void) saveImageInCache:(UIImage*) image forURL:(NSURL*)url{
// saves the image in cache for the url
}
Of course, this is only ONE POSSIBLE WAY to do it. I tried to make it simple, but there are plenty better and more complicated ways to do it.

Answer 2

Try it:
NSURL *imageURL = [NSURL URLWithString:#"www...."];
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
NSData *imageData = [NSData dataWithContentsOfURL:imageURL];
dispatch_async(dispatch_get_main_queue(), ^{
// Update the UI
self.imgVWprofile.image=[UIImage imageWithData:imageData];
});
});