问如何在iOS中查看从互联网下载数据的百分比？

EN

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)response;
    statusCode = [httpResponse statusCode];
    if ((statusCode/100) == 2) 
    {
        contentLength = [httpResponse expectedContentLength];
        if (contentLength == NSURLResponseUnknownLength) 
                NSLog(@"unknown content length %ld", contentLength);
    }

}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    bytesSum += [data length];
    percent = (float)bytesSum / (float)contentLength;

    // append the new data to the receivedData
    [receivedData appendData:data];     //received data is a NSMutableData ivar.

}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
     //the end. Write your data ( stored in receivedData ) to a local .mp3 file.
}