load images using SDWebImage in order

Question

After a lot of reading and recommendations, I am trying to implement SDWebImage framework in my app. I am able to download images from the server but the issue is that as the images are different sizes, they are not downloaded in the order that I call them (and would like them to be).

Here is the framework for reference: https://github.com/rs/SDWebImage

As you can see evidence of this from the print-line:

2013-08-20 11:11:01.785 Project[10785:c07] SD LOAD 1 array count = 1
2013-08-20 11:11:02.668 Project[10785:c07] SD LOAD 0 array count = 2
2013-08-20 11:11:02.946 Project[10785:c07] SD LOAD 3 array count = 3
2013-08-20 11:11:03.306 Project[10785:c07] SD LOAD 2 array count = 4
2013-08-20 11:11:03.862 Project[10785:c07] SD LOAD 4 array count = 5
2013-08-20 11:11:04.094 Project[10785:c07] SD LOAD 5 array count = 6
2013-08-20 11:11:04.793 Project[10785:c07] SD LOAD 6 array count = 7
2013-08-20 11:11:04.837 Project[10785:c07] SD LOAD 7 array count = 8
2013-08-20 11:11:05.046 Project[10785:c07] SD LOAD 8 array count = 9
2013-08-20 11:11:05.428 Project[10785:c07] SD LOAD 9 array count = 10

Below is my method:

-(void)sdWebLoadImages:(NSMutableArray*)imagesURLS{

    [_loadedImages removeAllObjects];
    NSMutableArray *tempArray = [[NSMutableArray alloc]init];
    _loadedImages = tempArray;
    for (int i=0;i<imagesURLS.count;i++){

    [_manager downloadWithURL:[imagesURLS objectAtIndex:i]
                     options:0
                    progress:^(NSUInteger receivedSize, long long expectedSize)
     {
         // progression tracking code
     }
                   completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType,BOOL finished)
     {
         if (image && finished)
         {

             [_loadedImages addObject:image];
            NSLog(@"SD LOAD %i array count = %i",i,_loadedImages.count);
         }
     }];
    }
}

How can I fix this (is it something in my for loop logic?). Also, I am trying to cancel all the downloads when a button is clicked, and am using [_manager cancelAll] but doesn't seem to work - any idea why?

Thanks fam!

ADDED:

The issue now is that the manager inserts all the cached images into the array first, causing the order to be disrupted, even after I set the setMaxConcurrentOperationCount to 1. Not sure how to keep the downloading in order even with cached images.

I'm not familiar with this framework. If it's using NSOperationQueue behind the scenes, can you set it so that maxOperations = 1? That way it won't run a bunch of parallel operations but will do them in the order you put them in the queue. — Daddy, Aug 20 '13 at 18:19
the [_manager downloadWithUrl...] returns an operation which i guess I can add to my own operationQ but it crashes when I try and do that so I'm kinda avoiding it at this time... — royherma, Aug 20 '13 at 18:27

score 2 · Accepted Answer · answered Aug 20 '13 at 18:31

2

As simple as ice and as pointed by 'Justin Amberson':

Go to SDWebImageDownloader.m

I am assuming you are using the latest SDWebImage library.

On line 72:

_downloadQueue.maxConcurrentOperationCount = NSOperationQueueDefaultMaxConcurrentOperationCount;

Change it to:

_downloadQueue.maxConcurrentOperationCount = 1;

It will download one image at a time.

Cheers

answered Aug 20 '13 at 18:31

Reno Jones

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Thanks Reno! Also, would all i need to is call [_manager cancelAll] to cancel the image loading for all of those requests? – royherma Aug 20 '13 at 18:34
Yes indeed: [[SDWebImageManager sharedManager] cancelAll] :) – Reno Jones Aug 20 '13 at 18:36
Looks like an opportunity to expose that property to the outside. – Daddy Aug 20 '13 at 18:46
there is still a problem. the download manager will load the cached images before the ones it needs to download and insert them into the array...messing up there order again! – royherma Aug 20 '13 at 22:15

load images using SDWebImage in order

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