试试这个：

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    // A response has been received,this is where we initialize the instance var you created
    // so that we can append data to it in the didReceiveData method
    // Furthermore,this method is called each time there is a redirect so reinitializing it
    // also serves to clear it
    lookServerResponseData = [[NSMutableData alloc] init];
}
 
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    // Append the new data to the instance variable you declared
    [lookServerResponseData appendData:data];
}
 
 
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    // The request is complete and data has been received
    // You can parse the stuff in your instance variable now
    NSError *errorJson=nil;
    NSDictionary* responseDict = [NSJSONSerialization JSONObjectWithData:lookServerResponseData options:kNilOptions error:&errorJson];
 
     NSLog(@"responseDict=%@",responseDict);
 
    [lookServerResponseData release];
    lookServerResponseData = nil;
}

这里,lookServerResponseData是全局声明的NSMutableData的实例.

希望它会有所帮助.