Very minimalistic fade-in implementation for AFNetworking's UIImageView category. Thanks to @myellow and @merowing_.

UIImageView+AFNetworkingFadeInAdditions.h

#import <AFNetworking.h>

@interface UIImageView (AFNetworkingFadeInAdditions)

- (void)setImageWithURL:(NSURL *)url placeholderImage:(UIImage *)placeholderImage fadeInWithDuration:(CGFloat)duration;

@end

UIImageView+AFNetworkingFadeInAdditions.m

#import "UIImageView+AFNetworkingFadeInAdditions.h"

@implementation UIImageView (AFNetworkingFadeInAdditions)

- (void)setImageWithURL:(NSURL *)url placeholderImage:(UIImage *)placeholderImage fadeInWithDuration:(CGFloat)duration {
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
    [request setHTTPShouldHandleCookies:NO];
    [request addValue:@"image/*" forHTTPHeaderField:@"Accept"];
    
    __weak typeof (self) weakSelf = self;
    
    [self setImageWithURLRequest:request placeholderImage:placeholderImage success:^(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image) {
        if (!request) // image was cached
            [weakSelf setImage:image];
        else
            [UIView transitionWithView:weakSelf duration:duration options:UIViewAnimationOptionTransitionCrossDissolve animations:^{
                [weakSelf setImage:image];
        } completion:nil];
    } failure:nil]; 
}

@end

Usage.markdown

Add AFNetworking to your project (eg. via cocoapods.org), copy these two files into your project, then

#import UIImageView+AFNetworkingFadeInAdditions.h

and use it like this:

[imageView setImageWithURL:myNSURL placeholderImage:someUIImageOrNil fadeInWithDuration:0.2f];

Will be using this in our Shindig app. Thanks very much for the contribution.

Getting an error after adding these two classes in my project.
No visible interface for UIImageview in line 12.Could you please help me out.

Thanks

Your check for cached vs. non-cache is not working... replaced with,

[self setImageWithURLRequest:request placeholderImage:placeholderImage success:^(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image) {
        UIImage *cachedImage = [[[weakSelf class] sharedImageCache] cachedImageForRequest:request];
        if (cachedImage) // image was cached
            [weakSelf setImage:image];
        else
            [UIView transitionWithView:weakSelf duration:duration options:UIViewAnimationOptionTransitionCrossDissolve animations:^{
                [weakSelf setImage:image];
        } completion:nil];
    } failure:nil]; ```

After tweaking your example, it seems to be that:

if (!request) // image was cached

should be changed to:

if (!response) // image was cached

AFNetworking returns a nil response, not a nil request when retrieved from the cache.