将图像从URL动态下载到UIImageVIew

Question

I am trying to insert and image into a UIImageView from a url. I used the following code to do so. When running the program gets stuck at

NSURL *url = [NSURL URLWithString:urlstring];

In the below code and it shows "Thread 1 : signal SIGABRT" on that particular line. Can someone help me with this and tell if the format that i used is correct or what i had did wrong??

-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = @"newoffer";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];
if (cell==nil)
{
    cell=[[UITableViewCell alloc]initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
}
NSDictionary *temp = [product objectAtIndex:indexPath.row];
UILabel *Label = (UILabel *)[cell viewWithTag:201];
Label.text = [temp objectForKey:@"item_name"];
UIImageView *Image = (UIImageView *)[cell viewWithTag:200];
NSString *urlstring=[temp objectForKey:@"image_url"];
NSURL *url = [NSURL URLWithString:urlstring];
NSData *data = [NSData dataWithContentsOfURL:url];
Image.image = [UIImage imageWithData:data];

return cell;

}

Answer 1

Change this code:

NSURL *url = [NSURL URLWithString:urlstring];
NSData *data = [NSData dataWithContentsOfURL:url];
Image.image = [UIImage imageWithData:data];

To:

 dispatch_queue_t myqueue = dispatch_queue_create("myqueue", NULL);

    // execute a task on that queue asynchronously
    dispatch_async(myqueue, ^{
NSURL *url = [NSURL URLWithString:[urlstring stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]];;
NSData *data = [NSData dataWithContentsOfURL:url];
 dispatch_async(dispatch_get_main_queue(), ^{
Image.image = [UIImage imageWithData:data]; //UI updates should be done on the main thread
     });
    });

As mentioned by others, an Image Caching library like SDWebImage will help a lot because even with this implementation, you just push the download process to a background thread so the UI does not get stucked, but you are not caching anything.

Answer 2

Try this

[image setImage:[UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:@"http://www.vbarter.com/images/content/1/9/19517.jpg"]]]];

For async downloading

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

[image setImage:[UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:@"http://www.vbarter.com/images/content/1/9/19517.jpg"]]]];

});

if url is dynamic then

NSString *stringUrl; // this can be any valid url as string

[image setImage:[UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:stringUrl]]]];

Answer 3

NSData *data = [NSData dataWithContentsOfURL:url];

will load imageData synchronous, that means main thread will be blocked .

Use the project on github: SDWebImage for image asynchronous loading and cache.

Answer 4

There's probably better libraries that do this now, but I have always been using this for my projects and it works well: AsyncImageView . There are other alternatives like SDWebImage

But basically, you don't want to use

NSData *data = [NSData dataWithContentsOfURL:url];

because it will block the main thread until the image is downloaded. To avoid this you might want to use something asynchronous, like the above two libraries.

For example, with AsyncImageView , it becomes as easy as:

myImageView.imageURL = someNSURL;