The most common way to load UIImage from the web - iphone

Question

Dear stackoverflowers,
I have gone astray.
In my app I load 2 images from the web, like this:
-(void)loadImages
{
...
image1 = [UIImage imageWithData:[NSData dataWithContentsOfURL:imgUrl1]];
image2 = [UIImage imageWithData:[NSData dataWithContentsOfURL:imgUrl2]];
}
In order to not blocking the main thread, I use GCD:
dispatch_async( dispatch_get_global_queue(0,0), ^{
[self loadImages];
After that, I use these images in my UITableView:
if (indexPath.row == 0)
{
cell.imageView.image = image1;
}
else
{
cell.imageView.image = image2;
}
Then I decided to add UIActivityIndicator, but faced some problems. I understand that my code is not correct. I saw that people using NSURLRequest and NSURLConnection to load images and add UIActivityIndicator.
Could you tell me please, what is the most standart way to load images like that ? What should I rewrite ?

Answer 1

I would suggest you to use AsyncImageView a beautiful implementation by Nicklockwood -father of iCarousel.
https://github.com/nicklockwood/AsyncImageView
it is very simple to use.
#import "AsyncImageView.h"
and in all imageViews do this.
[imageView setImage:#"default.png"];
[imageView setImageURL:#"whateverurl/whateverimage.png"];
In your case it would be:
[cell.imageView setImageURL:#"yourURL"];
It works like a charm, and my code is in production. But if you still want your code to work try this:
UIActivityIndicator *activity =[[UIActivityIndicator alloc] initWithStyle:UIActivityIndicatorWhite];
[activity setFrame:CGRectMake(100,100,30,30)];
[self.view addSubview:activity];
dispatch_queue_t dispatchQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0);
dispatch_async(dispatchQueue, ^(void)
{
[activity startAnimating];
[self loadImages];
dispatch_sync(dispatch_get_main_queue(), ^{
[yourTableView reloadData];
[activity stopAnimating];
[activty setHidden:YES];
});
});

Answer 2

I can tell you what I usually do if I want to use my own custom code
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
NSData * imageData = [NSData dataWithContentsOfURL:_pictureURL];
dispatch_async(dispatch_get_main_queue(), ^{
imageView.image = [UIImage imageWithData:imageData];
});
});
Otherwise you can consider the UIImageView+AFNetworking category that adds the method
setImageWithURLRequest:placeholderImage:success:failure:
to UIImageView.

Answer 3

There is nothing wrong with your code (assuming that you've confirmed that it works). Just because others use NSURLConnection and related doesn't make yours wrong.
To use the activity indicator do this:
-(void)loadImages
{
UIActivityIndicator *indicator = ...
...
[indicator startAnimating];
image1 = [UIImage imageWithData:[NSData dataWithContentsOfURL:imgUrl1]];
image2 = [UIImage imageWithData:[NSData dataWithContentsOfURL:imgUrl2]];
[indicator stopAnimating];
}
Small nit - personally I'd use:
cell.imageView.image = (0 == indexPath.row ? image1 : image2)
as nobody seems to appreciate the C 'conditional expressoin'. End small nit.