Getting an image from a remote server - iphone

Question

In my iPhone app I have to show the preview of the thumbnail image. That preview image actually we will get from remote server. Before loading that big image on screen I have to show preloading view but actually this preloading view is not appearing on the screen.
The code I used is:
zoomview=[[UIView alloc]initWithFrame:CGRectMake(0,0,320,460)];
imageloadview.backgroundColor=[UIColor colorWithRed:0.0 green:0.0 blue:0.0 alpha:0.5];
[self.view addSubview:imageloadview];
[activity startAnimating];
[self loadimageview];
Here instead of loading the zoom view on screen this loading view method is executing but I want to display preloading view before getting the big image from the server.
-(void)loadimageview
{
imageloader.image=[UIImage imageNamed:#""];
[self loadimage];
}
-(void)loadimage
{
NSData *data=[NSData dataWithContentsOfURL:[NSURL URLWithString:[picfullarray objectAtIndex:0]]];
if([data length]==0)
{
NSLog(#"data");
}
else
{
UIImage *image1=[UIImage imageWithData:data];
imageloader.image=image1;
[activity stopAnimating];
[loadlabel1 setText:#""];
}
}
How do I show preloaded view on iPhone screen before getting the big image from the server?

Answer 1

You have to load the image asynchronously with NSURLRequest.
Make the class implement NSURLRequestDelegate protocol. In the function - (void)connectionDidFinishLoading:(NSURLConnection *)connection of NSURLRequestDelegate, add the code to update the view when the loading is completed.
// You must declare NSMutableData somewhere to write received data in delegate method
// - (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
// I assume the instance of NSMutableData is named data
// If you want to load multiple images, it is a bit tricky, but doable.
// I'll post the code if that is what you need.
- (void) connectionDidFinishLoading: (NSURLConnection *) connection {
// You may want to declare a instance member to store the image (UIImage*), so that you can restore the view if the view is unloaded due to memory warning.
UIImage* image = [UIImage imageWithData: data];
data = nil; // Important. You should clean the data, or it will take up space.
// You may want to check whether image != nil, since the incoming data may not be image
[self displayImage: image];
}
- (void) displayImage: (UIImage*) aImage {
imageloader.image = aImage;
// Depending on how UIImageView is initialized, you may need to call sizeToFit.
// Or set the frame accordingly
[activity stopAnimating];
[loadlabel1 setText: #""];
}

Answer 2

I'd suggest using SDWebImage framework. It already has async image loading capability, and it's super easy to use.
[imageView.image setImageWithURL:[NSURL URLWithString:#"http://www.domain.com/path/to/image.jpg"]
placeholderImage:[UIImage imageNamed:#"placeholder.png"]];
You don't have to worry about messing with NSURLConnection, maintaining NSData, etc..

Answer 3

There is also AFNetworking which has a way to do this easily.
https://github.com/AFNetworking/AFNetworking/wiki/Getting-Started-with-AFNetworking
Check out the "Download and Display Images" section.