How to load images from API/URL asynchronously?

Question

I am fetching images synchronously from an array which stores URLs of images but it work very slowly. Now i want to load them asynchronously for fast working.

Heres the code and provide answer with coding.

#import "DetailViewController.h"
#import "FinalViewController.h"

@interface DetailViewController ()

@end

@implementation DetailViewController
@synthesize jsonData;

- (void)viewDidLoad {
    [super viewDidLoad];
    self.title =  @"Select a Photo";

    // Do any additional setup after loading the view.
    [UIApplication sharedApplication].networkActivityIndicatorVisible = YES;

    NSURL *url = [NSURL URLWithString:@"http://json.code.com/albums/1/photos"];
    NSURLRequest *request = [NSURLRequest requestWithURL:url];
    [[NSURLConnection alloc] initWithRequest:request delegate:self];


}

-(void)connection:(NSURLConnection *)connection didReceiveResponse:(nonnull NSURLResponse *)response
{
    data1 = [[NSMutableData alloc] init];
}


-(void)connection:(NSURLConnection *)connection didReceiveData:(nonnull NSData *)theData
{
    [data1 appendData:theData];
}

-(void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;

    jsonArray1 = [NSJSONSerialization JSONObjectWithData:data1 options:nil error:nil];
    [mainTableView reloadData];

}


-(void)connection:(NSURLConnection *)connection didFailWithError:(nonnull NSError *)error
{
    UIAlertView *errorView = [[UIAlertView alloc]initWithTitle:@"Error" message:@"Please make sure you are connected to either 3G or Wi-Fi." delegate:nil cancelButtonTitle:@"Dismiss" otherButtonTitles:nil, nil];
    [errorView show];
    [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
}



- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

- (int)numberOfSectionInTableView:(UITableView *)tableView
{
    return 1;
}

- (int) tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    return  [jsonArray1 count];
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(nonnull NSIndexPath *)indexPath
{
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"Cell"];
    if (cell == nil) {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:@"Cell"];
    }

    cell.textLabel.text = [[jsonArray1 objectAtIndex:indexPath.row] objectForKey:@"title"];
    cell.detailTextLabel.text = [NSString stringWithFormat:@"URL : %@", [[jsonArray1 objectAtIndex:indexPath.row] objectForKey:@"url"]];

    NSURL *URL = [[NSURL alloc] initWithString:[[jsonArray1 objectAtIndex:indexPath.row] valueForKey:@"thumbnailUrl"]];

    NSData *URLData = [[NSData alloc] initWithContentsOfURL:URL];
    [[cell imageView]setImage:[UIImage imageWithData:URLData]];


    return cell;
}


-(void)tableView:(UITableView *)tableview didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    FinalViewController *fvc = [[FinalViewController alloc] initWithNibName:@"FinalViewController" bundle:nil];
    fvc.jsonData2 = [jsonArray1 objectAtIndex:indexPath.row];
    [self.navigationController pushViewController:fvc animated:YES];

}


@end

use github.com/rs/SDWebImage

kb920
– kb920

2015-11-10 04:29:50 +00:00
Commented Nov 10, 2015 at 4:29 — kb920
– kb920, Commented Nov 10, 2015 at 4:29

Janmenjaya · Accepted Answer · 2021-12-21 11:48:45Z

1

We can use dispatch_async to run the operation asynchronously.

Try this:

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{

    myCell *cell = [tableView dequeueReusableCellWithIdentifier:@"cell"];
    if (cell == nil) {
        cell = [[myCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:@"cell"];
    }

    cell.poster.image = nil; // or cell.poster.image = [UIImage imageNamed:@"placeholder.png"];

    dispatch_async(kBgQueue, ^{
        NSData *imgData = [NSData dataWithContentsOfURL:[NSURL URLWithString:[NSString stringWithFormat:@"http://myurl.com/%@.jpg",[[myJson objectAtIndex:indexPath.row] objectForKey:@"movieId"]]]];
        if (imgData) {
            UIImage *image = [UIImage imageWithData:imgData];
            if (image) {
                dispatch_async(dispatch_get_main_queue(), ^{
                    myCell *updateCell = (id)[tableView cellForRowAtIndexPath:indexPath];
                    if (updateCell)
                        updateCell.poster.image = image;
                });
            }
        }
    });
    return cell;
}

edited Dec 21, 2021 at 11:48

answered Nov 10, 2015 at 4:27

Janmenjaya

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2 Comments

halfer Over a year ago

Would you be able to edit this to explain why it might help the reader? What change did you make in this code, or what feature would you draw readers' attention to?

Janmenjaya Over a year ago

@halfer My intention was to make the reader aware of "dispatch_async" by using which we can achieve asynchronous operation. I have edited the answer with attention point. Thanks

Community · Accepted Answer · 2017-05-23 12:32:47Z

0

You can do like this:

cell.tag = indexPath.row;
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul);
dispatch_async(queue, ^(void) {

    NSData *imageData = [NSData dataWithContentsOfURL: URL];

    UIImage* image = [[UIImage alloc] initWithData:imageData];
    if (image) {
         dispatch_async(dispatch_get_main_queue(), ^{
             if (cell.tag == indexPath.row) {
                 cell.imageView.image = image;
                 [cell setNeedsLayout];
             }
         });
     }
});

Ref: Asynchronous downloading of images for UITableView with GCD

edited May 23, 2017 at 12:32

CommunityBot

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answered Nov 10, 2015 at 4:24

tuledev

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5 Comments

Navjot Singh Over a year ago

Can you please help me in putting activity indicator view on the view till photos are loading. need coded help. thanks

tuledev Over a year ago

I'm thinking about the "the first row is not visible, all the rest are visible now" (maybe not same as origin). Haha.

tuledev Over a year ago

@NavjotSingh activity indicator, maybe you should post another question. Easy for following.

Navjot Singh Over a year ago

i can't put more then one question in one day .

tuledev Over a year ago

@NavjotSingh well, I don't know that. In my opinion, you shouldn't use indicator. You should use a default image(like placeholder) when loading.

user5553647 · Accepted Answer · 2016-09-09 06:17:26Z

0

Just by simply setting the following works fine for me .

cell.imageView.image =[UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:[NSString stringWithFormat:@"%@",[imageArray objectAtIndex:i]]]]];

You can use the activity indicator as you have asked . Just drag and drop UIActivityIndicatorView onto the UIImageView of the UITableViewCell and set the needed constraints . Once the image gets loaded you can set it as hidden .

To do it programmatically , you can add a subview to the Image view in the UITableViewCell. Once the Image gets loaded you can remove the sub view .

UIActivityIndicatorView* actInd = [[UIActivityIndicatorView alloc]init];
[cell.imageView addSubview:actInd];

edited Sep 9, 2016 at 6:17

answered Sep 9, 2016 at 6:09

user5553647

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