====== 파일다운로드 ======
  * 레퍼런스 : [[http://developer.apple.com/documentation/Cocoa/Conceptual/URLLoadingSystem/Tasks/UsingNSURLDownload.html#//apple_ref/doc/uid/20001839-BAJEAIEE|NSURLDownload]]


NSURLDownload 를 사용해서 사용하려는 URL로부터 컨텐츠를 디스크로 저장하는 기능을 제공. NSURLConnection 과 유사하지만 저장하려는 파일을 명시하는 기능이 추가되었음. 

또한 MacBinary, BinHex and gzip 와 같은 인코딩을 디코딩하는 기능이 가능함. NSURLConnection 와 달리 NSURLDownload는 캐쉬에 데이터를 저장하지 않음.

Note: 파운데이션 클래스를 쓰는데 문제가 없다면 NSURLDownlolad의 서브클래스인 Web Kit framework 의 WebDownload를 사용해서 인증 인터페이스를 사용할 수 있다.

Contents: 친절한 예제코드가 있음

  * [[http://developer.apple.com/documentation/Cocoa/Conceptual/URLLoadingSystem/Tasks/UsingNSURLDownload.html#//apple_ref/doc/uid/20001839-165459|Downloading to a Predetermined Destination]]
  * [[http://developer.apple.com/documentation/Cocoa/Conceptual/URLLoadingSystem/Tasks/UsingNSURLDownload.html#//apple_ref/doc/uid/20001839-163723|Downloading a File Using the Suggested Filename]]
  * [[http://developer.apple.com/documentation/Cocoa/Conceptual/URLLoadingSystem/Tasks/UsingNSURLDownload.html#//apple_ref/doc/uid/20001839-165094|Displaying the Download Progress]]
  * [[http://developer.apple.com/documentation/Cocoa/Conceptual/URLLoadingSystem/Tasks/UsingNSURLDownload.html#//apple_ref/doc/uid/20001839-155583|Handling Request Changes]]
  * [[http://developer.apple.com/documentation/Cocoa/Conceptual/URLLoadingSystem/Tasks/UsingNSURLDownload.html#//apple_ref/doc/uid/20001839-155724|Handling Authentication Challenges]]
  * [[http://developer.apple.com/documentation/Cocoa/Conceptual/URLLoadingSystem/Tasks/UsingNSURLDownload.html#//apple_ref/doc/uid/20001839-165205|Decoding Encoded Files]]
===== Downloading to a Predetermined Destination =====

One usage pattern for NSURLDownload is downloading a file to a predetermined filename on the disk. 
If the application knows the destination of the download, it can explicitly set it using setDestination:allowOverwrite:. Multiple setDestination:allowOverwrite: messages to an NSURLDownload instance are ignored.

The download starts immediately upon receiving the initWithRequest:delegate: message. It can be canceled any time before the delegate receives a downloadDidFinish: or download:didFailWithError: message by sending the download a cancel message.

The example in Listing 1 sets the destination, and thus requires the delegate only implement the download:didFailWithError: and downloadDidFinish: methods.

<code objectivec>
- (void)startDownloadingURL:sender
{
    // create the request
    NSURLRequest *theRequest = 
        [NSURLRequest requestWithURL:[NSURL URLWithString:CONFIG_SOURCE_URL_STRING]
                                              cachePolicy:NSURLRequestUseProtocolCachePolicy
                                          timeoutInterval:60.0];
    // create the connection with the request
    // and start loading the data
    NSURLDownload  *theDownload = [[NSURLDownload alloc] initWithRequest:theRequest delegate:self];
    if (theDownload) {
        // set the destination file now
        [theDownload setDestination:CONFIG_SOURCE_PATH allowOverwrite:YES];
    } else {
        // inform the user that the download could not be made
    }
}
 
- (void)download:(NSURLDownload *)download didFailWithError:(NSError *)error
{
    // release the connection
    [download release];
 
    // inform the user
    NSLog(@"Download failed! Error - %@ %@",
          [error localizedDescription],
          [[error userInfo] objectForKey:NSErrorFailingURLStringKey]);
}
 
- (void)downloadDidFinish:(NSURLDownload *)download
{
    // release the connection
    [download release];
 
    // do something with the data
    NSLog(@"%@",@"downloadDidFinish");
}
</code>