ios - nsurlconnection を使用して 1 つずつダウンロードします

Question

NSURLconnection を使用して複数のファイルを 1 つずつダウンロードしたいのですが、ダウンロードできる最大数は 5 です。このプロセスは、最初のダウンロードを開始し、最初のダウンロードが完了したら 2 番目のダウンロードのみを開始し、2 番目のダウンロードが完了したら 3 番目のダウンロードを開始するようなものです。同様に、4 回目のダウンロードと 5 回目のダウンロードでも、1 つのファイルをダウンロードできます。同じコードは次のとおりです。

- (IBAction)download1:(id)sender {
    _fileName = @"dog-wallpaper-dogs.jpg";
    _currentURL = [NSString stringWithFormat:@"http://noruffdaysdotcom1.files.wordpress.com/2012/04/%@",_fileName];
    NSLog(@"currenturl%@",_currentURL);

    NSLog(@"the filename is %@",_fileName);

    NSURL *url =[NSURL URLWithString:_currentURL];
    NSURLRequest *theRequest = [NSURLRequest requestWithURL:url cachePolicy:NSURLRequestReloadIgnoringCacheData timeoutInterval:60];

    _receivedData = [[NSMutableData alloc]initWithLength:0];
    NSURLConnection *connection = [[NSURLConnection alloc]initWithRequest:theRequest delegate:self startImmediately:YES];


}

-(void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)response;
    NSLog(@"THE STATUS CODE IS %d",[httpResponse statusCode]);
    statuscode = [httpResponse statusCode];
    NSLog(@"into didReceiveResponse");
    [UIApplication sharedApplication].networkActivityIndicatorVisible = YES;
    [_receivedData setLength:0];
    expectedBytes = [response expectedContentLength];
    NSLog(@"EXPECTED BYTES:%ld",expectedBytes);
}
-(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
   // NSLog(@"into did receivedata");
    [_receivedData appendData:data];
    //   float progressive = (float)[_receivedData length] / (float)expectedBytes;


}

-(void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
    flag= 0;
    NSLog(@"into didfailwitherror");
    [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
    NSLog(@"connection failed");
}

-(NSCachedURLResponse *)connection:(NSURLConnection *)connection willCacheResponse:(NSCachedURLResponse *)cachedResponse
{
    return nil;
}

-(void)connectionDidFinishLoading:(NSURLConnection *)connection

{   flag = 0;
    NSLog(@"into didfinishloading");
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    NSLog(@"DOCUMENT DIRECTORY :%@",documentsDirectory);
    //   [NSFileManager isWritbleAtPath:documentsDirectory];
    //  [NSFileManager isWritableAtPath:documentsDirectory];
    _imagePath = [documentsDirectory stringByAppendingPathComponent:_fileName];
    NSLog(@"iamge path:%@",_imagePath);
    NSLog(@"succeeded");
    [UIApplication sharedApplication].networkActivityIndicatorVisible= NO;
    NSLog(@"Succeeded! Received %d bytes of data",[_receivedData length]);

    // flag= [_receivedData writeToFile:imagePath atomically:NO];
    if([_receivedData writeToFile:_imagePath atomically:YES])
    {
        flag= 1;
        NSLog(@"write successfull");

    }
    else{
        flag =0;
        NSLog(@"write failed");
    }
    UIImage *img =[UIImage imageWithContentsOfFile:_imagePath];
    self.imageview.image = img;
    isloaded = YES;
}

以前の完了時に次のダウンロードを行う方法を教えてください。