ios: image cache and retrieval

Question

I wish to implement caching feature for an image in iOS. I wish to create a sample app for that, just for my understanding.

Here is what I want to do:

Get a high resolution image from internet and cache it, display it.
Now next time when this ViewController loads up, the image should be loaded from cache and not from internet.

I know how to cache an image using SDWebImage framework. I wish to try it with NSCache.

How can I implement it using NSCache? Examples are welcomed.

EDITED :

    - (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view from its nib.
    NSCache *cache = [self imageCache];

    NSURL *url = [NSURL URLWithString:@"http://i1.ytimg.com/vi/YbT0xy_Jai0/maxresdefault.jpg"];
    NSData *data = [NSData dataWithContentsOfURL:url];
    UIImage *image = [[UIImage alloc] initWithData:data];

    NSString *imagePath = @"http://i1.ytimg.com/vi/YbT0xy_Jai0/maxresdefault.jpg";
//    UIImage *image;
    if (!(image = [cache objectForKey:imagePath])) { // always goes inside condition
        // Cache miss, recreate image
        image = [[UIImage alloc] initWithData:data];
        if (image) {    // Insert image in cache
            [cache setObject:image forKey:imagePath]; // cache is always nil
        }
    }
    _imgCache.image = image;

here it is i put example about NSCache please visit this http://stackoverflow.com/questions/19326284/what-is-the-proper-way-to-use-nscache-with-dispatch-async-in-a-reusable-table-ce/19326565#19326565 — Nitin Gohel, Apr 17 '14 at 12:29

Midhun MP · Accepted Answer · 2014-04-17T12:58:42.553

5

You can add image to cache using and Id:

[imageCache setObject:image forKey:@"myImage"];

Later you can retreive the image by using:

UIImage *image = [imageCache objectForKey:@"myImage"];

Entire flow will be like:

UIImage *image = [imageCache objectForKey:@"myImage"];
if (!image)
{
   // download image
   dispatch_async(dispatch_get_global_queue(0, 0), ^{
       NSData *imageData = [NSData dataWithContentsOfURL:[NSURL URLWithString:yourURL]];
       if (imageData)
       {
           // Set image to cache
           [imageCache setObject: [UIImage imageWithData:imageData] forKey:@"myImage"];
           dispatch_async(dispatch_get_main_queue(), ^{
               [yourImageView setImage:[UIImage imageWithData:imageData]];
           });
        }
    });
}
else
{
   // Use image from cache
   [yourImageView setImage:image];
}

edited Apr 17 '14 at 12:58

answered Apr 17 '14 at 12:30

Midhun MP

103,496
31
153
200

You can use GCD for that : https://developer.apple.com/library/ios/documentation/Performance/Reference/GCD_libdispatch_Ref/Reference/reference.html – Midhun MP Apr 17 '14 at 12:54
@z22: I have updated the answer, you need to give dynamic id's – Midhun MP Apr 17 '14 at 12:59
thanks a lot. But please check my edited question. I have given the code I am using. Cache is always nil, so image always gets downloaded from internet. Why is this happening? Let me know where I am getting wrong. – z22 Apr 17 '14 at 13:01
@z22: did you allocate the cache ? If no then use : `cache = [[NSCache alloc] init];` – Midhun MP Apr 17 '14 at 13:03
I allocated cache as you said, but its still the same. Where am I getting wrong? – z22 Apr 17 '14 at 13:05
@z22: from where you are getting cache as null ? – Midhun MP Apr 17 '14 at 13:18
Its done. I took the cache variable in appDelegate and initialized it there. Thanks a lot mate! – z22 Apr 17 '14 at 13:25
@z22: with pleasure :) – Midhun MP Apr 17 '14 at 13:35

score 0 · Answer 2 · answered Apr 17 '14 at 12:56

0

Refer the sample code to load image asynchronously and image caching,

https://developer.apple.com/library/ios/samplecode/LazyTableImages/Introduction/Intro.html

answered Apr 17 '14 at 12:56

Sathish Kumar

219
1
10

ios: image cache and retrieval

2 Answers2