Question

UIImagePickerController freezes while I think the Image is being compressed or being sent by NSURLConnection although I’m not convinced it’s the later.

What I want is, all this to be done in the background. Instead when I pick a photo from the library, the Screen freezes for what feels like forever. This isn’t optimal, obviously. What approach should I take here?

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingImage:(UIImage *)img editingInfo:(NSDictionary *)editInfo
{
int i = 0;
NSString *uniquePath = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents/selectedImage.png"];

while ([[NSFileManager defaultManager] fileExistsAtPath:uniquePath])
{
    uniquePath = [NSString stringWithFormat:@"%@/%@-%d.%@", [NSHomeDirectory() stringByAppendingPathComponent:@"Documents"], @"selectedImage", ++i, @"png"];
}

NSLog(@"Writing selected Image to Documents Folder, %@", uniquePath);

dataForPNGFile = UIImagePNGRepresentation(img);

if (!dataForPNGFile) return NO;

[UIImagePNGRepresentation(img) writeToFile:uniquePath atomically:YES];
UIImageWriteToSavedPhotosAlbum(img, nil, nil, nil);
[[self parentViewController] dismissModalViewControllerAnimated:YES];
[picker release];

NSString *urlString = @"http://localhost:3000/photos";
NSURL *url = [NSURL URLWithString:urlString];
NSString *boundary = @"----1010101010";
NSString *contentType = [NSString stringWithFormat:@"multipart/form-data; boundary=%@",boundary];

NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
[request setHTTPMethod:@"POST"];
[request addValue:contentType forHTTPHeaderField: @"Content-Type"];

NSString *photoPath = [[NSBundle mainBundle] pathForResource:@" my-photo " ofType:@"jpg"];
NSData *photoData = [NSData dataWithContentsOfFile:photoPath];

NSMutableData *body = [NSMutableData data];
[body appendData:[[NSString stringWithFormat:@"--%@\r\n", boundary] dataUsingEncoding:NSUTF8StringEncoding]];
[body appendData:[@"Content-Disposition: form-data; name=\"photo-description\"\r\n\r\n" dataUsingEncoding:NSUTF8StringEncoding]];
[body appendData:[@"testing 123" dataUsingEncoding:NSUTF8StringEncoding]];
[body appendData:[[NSString stringWithFormat:@"\r\n--%@\r\n", boundary] dataUsingEncoding:NSUTF8StringEncoding]];
//  [body appendData:[[NSString stringWithFormat:@"Content-Disposition: form-data; name=\"photo-file\"; filename=\"%@\"\r\n", " my-photo.jpg"] dataUsingEncoding:NSUTF8StringEncoding]];
[body appendData:[@"Content-Type: image/jpeg\r\n\r\n" dataUsingEncoding:NSUTF8StringEncoding]];
[body appendData:photoData];
[body appendData:[[NSString stringWithFormat:@"\r\n--%@\r\n", boundary] dataUsingEncoding:NSUTF8StringEncoding]];
[body appendData:[@"Content-Disposition: form-data; name=\"tags\"\r\n\r\n" dataUsingEncoding:NSUTF8StringEncoding]];
[body appendData:[@"random,test,example" dataUsingEncoding:NSUTF8StringEncoding]];
[body appendData:[[NSString stringWithFormat:@"\r\n--%@--\r\n",boundary] dataUsingEncoding:NSUTF8StringEncoding]];
[request setHTTPBody:body];
[request addValue:[NSString stringWithFormat:@"%d", body.length] forHTTPHeaderField: @"Content-Length"];

[[NSURLConnection alloc] initWithRequest:request delegate:self];

}

Answer 1

You should use:

detachNewThreadSelector:toTarget:withObject:

Detaches a new thread and uses the specified selector as the thread entry point.

+ (void)detachNewThreadSelector:(SEL)aSelector toTarget:(id)aTarget withObject:(id)anArgument

Documentation here: NSThread

This will create a new thread for the operation that is eating up the cpu, so your UI isn’t affected remember to create a NSAutoreleasePool for the new thread, as only the main thread gets a NSAutoreleasePool pool by default.

So at the beginning of your selector do:

NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

//and at the end:

[pool drain]: