iPhone: How to get a UIImage from a url?

Question

How do you download an image and turn it into a UIImage?

Answer 1

NSURL *url = [NSURL URLWithString:@"http://example.com/image.jpg"];
NSData *data = [NSData dataWithContentsOfURL:url];
UIImage *img = [[[UIImage alloc] initWithData:data] autorelease];

However, this isn't asynchronous.

Answer 2

You should keep in mind that loading the image data with the sample code you've provided in your own answer will block the main thread until the download has completed. This is a useability no-no. The users of your app will think your app is unresponsive. If you want to download an image, prefer NSURLConnection to download it asynchronously in its own thread.

Read the Apple documentation about async downloads with NSURLConnection.

When your download completes, you can then instantiate your UIImage from the data object:

- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    if (requestData)
    {
        self.image = [[[UIImage alloc] initWithData:requestData] autorelease];
    }
}

Where requestData and image are instance variables of your containing class, and image is a retained property. Be sure to release image in the dealloc routine of the class, e.g. using self.image=nil;.

Answer 3

It is true that Asynchronous loading is a must, but you can also achieve that with a background call if you just need a simple solution.

[self performSelectorInBackground:@selector(loadImage) withObject:nil];

- (void)loadImage
{
   NSURL * url = [NSURL URLWithString:@"http://.../....jpg"];
   NSData * data = [NSData dataWithContentsOfURL:url];
   UIImage * image = [UIImage imageWithData:data];
   if (image)
   {
       // Success use the image
       ...
   }
   else
   {
       // Failed (load an error image?)
       ...
   }
}