Asynchronous download/request with Objective-C

For handling asynchronous request there is a very neat and simple mechanism in Objective-C.

Delegates

The following header file defines a protocol for the delegate and the necessary methods and data types to create a downloader that constantly pushes an update about the download state to the main thread.

Header File

@protocol DownloaderDelegate; #import <Foundation/Foundation.h> @interface Downloader : NSObject { id <DownloaderDelegate> delegate; NSString* strFileNameWithPath; NSURLConnection* connection; CGFloat floatTotalData; CGFloat floatReceivedData; } @property(nonatomic, retain) NSString* strFileNameWithPath; @property(nonatomic, retain) id <DownloaderDelegate> delegate; -(void)loadData; -(float)getProgressInPercent; @end @protocol DownloaderDelegate <NSObject> @optional -(void)didReceiveData:(Downloader *)d; //will be called each time data has been received -(void)didLoadData:(Downloader *)d; //will be called when the download has finished @end

Implementation

#import "Downloader.h" @implementation Downloader @synthesize strFileNameWithPath; @synthesize delegate; -(void)loadData{ floatTotalData = 100; floatReceivedData = 0; self.strFileNameWithPath = [[NSHomeDirectory() stringByAppendingPathComponent:@"Documents"] stringByAppendingPathComponent:@"tmp"]; self.strFileNameWithPath = [self.strFileNameWithPath stringByAppendingPathComponent:@"someFile.zip"]; [[NSFileManager defaultManager] createFileAtPath:self.strFileNameWithPath contents:nil attributes:nil]; NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:@"http://url.com/getData.php"]]; //this block shall show how to add POST variables to the request NSString *encodedParameterPairs = [NSString stringWithFormat:@"uid=%@", [[UIDevice currentDevice] uniqueIdentifier]]; NSData *requestData = [encodedParameterPairs dataUsingEncoding:NSUTF8StringEncoding allowLossyConversion:YES]; [request setHTTPMethod: @"POST"]; [request setHTTPBody:requestData]; [NSURLConnection connectionWithRequest:request delegate:self]; //request is send here } - (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response { //store how big file is going to be floatTotalData = [[NSString stringWithFormat:@"%lli",[response expectedContentLength]] floatValue]; } - (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data { floatReceivedData += [data length]; //add new data to the end of the file NSFileHandle *fileHandle = [NSFileHandle fileHandleForUpdatingAtPath: self.strFileNameWithPath]; [fileHandle seekToEndOfFile]; [fileHandle writeData: data]; [fileHandle closeFile]; //if delegate did implement the method didReceiveData let him know about the new data if ([self.delegate respondsToSelector:@selector(didReceiveData:)]) [self.delegate didReceiveData:self]; } - (void)connectionDidFinishLoading:(NSURLConnection *)connection { //do something with the received data.... //and let the delegate know that the download has finished if ([self.delegate respondsToSelector:@selector(didLoadData:)]) [self.delegate didLoadData:self]; } -(float)getProgressInPercent{ //if you want to show a progressbar or something similar call this method in //the delegate method didReceiveData return (floatReceivedData / floatTotalData) * 100.0f; } - (void)dealloc { //free memory [strFileNameWithPath release], strFileNameWithPath = nil; delegate = nil; [super dealloc]; } @end

This implementation is ment for big files like 200 MB zip files. If you just want to download small stuff like an image u can instead of writing into a file use a NSData object.

Hope this tutorial did help. Feel free to post some code improvements or questions in the comments?

P.S.: Will look for a nicer way to post code in blogger. For the moment I don't have a lot of time (child n.3 was born two days ago... ;o) ) so ill leave it this way.


Cheers,

JayEs

Here the code as Pastie-link:

header-file
implementation