Download File Asynchronously

利用NSURLConnection的initWithRequest:delegate:startImmediately: method建立connection，

於startImmediately傳入yes表示馬上開始download

NSURL *url = [NSURL URLWithString:urlStr];

self.downloadData = [[NSMutableData alloc] init];

[self.downloadData release];

NSURLRequest *req = [NSURLRequest requestWithURL:url];

self.downloadConnection = [[NSURLConnection alloc] 

                                   initWithRequest:req  

                                   delegate:self

                                   startImmediately:YES];

[self.downloadConnection release];


常用的NSURLConnectionDelegate method


開始download後，首先被呼叫的method
由於一個request可能收到多個response，
所以將data的長度設為0，
清除之前收到的data

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response

{

    NSLog(@"didReceiveResponse");

    [self.downloadData setLength:0];

}

將收到的data累加進downloadData

-(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data

{

    NSLog(@"data %d", [data length]);

    [self.downloadData appendData:data];

}

成功完成下載時被呼叫

- (void)connectionDidFinishLoading:(NSURLConnection *)connection

{

    NSLog(@"Successfully connectionDidFinishLoading");

}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error

{

    NSLog(@"error %@", error);

}

測試輸出:

2011-03-26 17:50:00.690 DownloadAsync[13125:207] didReceiveResponse

2011-03-26 17:50:00.692 DownloadAsync[13125:207] data 3310

2011-03-26 17:50:00.693 DownloadAsync[13125:207] data 13258

2011-03-26 17:50:00.694 DownloadAsync[13125:207] Successfully connectionDidFinishLoading