Getting Image from URL Objective C

Question

I'm trying to get an image from an URL and it doesn't seem to be working for me. Can someone point me in the right direction?

Here is my code:

NSURL *url = [NSURL URLWithString:@"http://myurl/mypic.jpg"];

NSString *newIMAGE = [[NSString alloc] initWithContentsOfURL:url
                                       encoding:NSUTF8StringEncoding error:nil];

cell.image = [UIImage imageNamed:newIMAGE];

When I debug the newIMAGE string is nil so something isn't working there.

Answer 1

What you want is to get the image data, then initialize a UIImage using that data:

NSData * imageData = [[NSData alloc] initWithContentsOfURL: [NSURL URLWithString: @"http://myurl/mypic.jpg"]];
cell.image = [UIImage imageWithData: imageData];
[imageData release];

As requested, here's an asynchronous version:

dispatch_async(dispatch_get_global_queue(0,0), ^{
    NSData * data = [[NSData alloc] initWithContentsOfURL: [NSURL URLWithString: @"http://myurl/mypic.jpg"]];
    if ( data == nil )
        return;
    dispatch_async(dispatch_get_main_queue(), ^{
        // WARNING: is the cell still using the same data by this point??
        cell.image = [UIImage imageWithData: data];
    });
    [data release];
});

Answer 2

Ok there's a couple of things wrong here:

1. The conversion from URL (url) to NSString (newImage) is incorrect, what the code actually does there is try to load the contents of "http://myurl/mypic.jpg" into the NSString.

2. The -imageNamed method takes a string that is a path of a local file, not a URL as an argument.

You need to use an NSData object as an intermediary, like in this example: http://blogs.oreilly.com/digitalmedia/2008/02/creating-an-uiimage-from-a-url.html

Answer 3

the accepted answer asynchronous version worked very slow in my code. an approach using NSOperation worked light years faster. the code provided by Joe Masilotti --> objective - C : Loading image from URL? (and pasted below):

-(void) someMethod {
    // set placeholder image
    UIImage* memberPhoto = [UIImage imageNamed:@"place_holder_image.png"];

    // retrieve image for cell in using NSOperation
    NSURL *url = [NSURL URLWithString:group.photo_link[indexPath.row]];
    [self loadImage:url];
}

- (void)loadImage:(NSURL *)imageURL
{
    NSOperationQueue *queue = [NSOperationQueue new];
    NSInvocationOperation *operation = [[NSInvocationOperation alloc]
                                        initWithTarget:self
                                        selector:@selector(requestRemoteImage:)
                                        object:imageURL];
    [queue addOperation:operation];
}

- (void)requestRemoteImage:(NSURL *)imageURL
{
    NSData *imageData = [[NSData alloc] initWithContentsOfURL:imageURL];
    UIImage *image = [[UIImage alloc] initWithData:imageData];

    [self performSelectorOnMainThread:@selector(placeImageInUI:) withObject:image waitUntilDone:YES];
}

- (void)placeImageInUI:(UIImage *)image
{
    [self.memberPhotoImage setImage:image];
}

Answer 4

In Swift 3 and 4

let theURL = URL(string:"https://exampleURL.com")
let imagedData = NSData(contentsOf: theURL!)!
let theImage = UIImage(data: imagedData as Data)
cell.theImageView.image = theImage

This will be done in the main thread.

And to perform the same in asynchronous/background thread

   DispatchQueue.main.async(){
      let theURL = URL(string:"https://exampleURL.com")
      let imagedData = NSData(contentsOf: theURL!)!
      let theImage = UIImage(data: imagedData as Data)
   }
   cell.theImageView.image = theImage

Answer 5

Updating upon Jim dovey answer,[data release] is no longer required because in the updated apple guidelines. Memory management is done automatically by ARC (Automatic counting reference) ,

Here is the updated asynchronous call,

dispatch_async(dispatch_get_global_queue(0,0), ^{
        NSData * data = [[NSData alloc] initWithContentsOfURL: [NSURL URLWithString: @"your_URL"]];
        if ( data == nil )
            return;
        dispatch_async(dispatch_get_main_queue(), ^{
            self.your_UIimage.image = [UIImage imageWithData: data];
        });

    });