为什么我的委托方法永远不会被调用？

Question

我正在关注这些问题和教程：

• fetching data with get post methods
• sending http get and post from cocoa
• nsurlconnection basics for beginners
• sending an http post request on ios
• how to hanlde multiple delegates

但我仍然缺少一些东西。我的委托方法

- (void)connectionDidFinishLoading:(NSURLConnection *)connection

一直被调用，需要一点时间，我猜是因为网速，但是方法

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

永远不会被调用。我错过了什么？请帮帮我。

我的代码：

-(void)loadDataBase{
    NSString *post = [NSString stringWithFormat:@"advnr=123"];
    NSData *postData = [post dataUsingEncoding:NSASCIIStringEncoding allowLossyConversion:YES];
    NSString *postLength = [NSString stringWithFormat:@"%lu",(unsigned long)[postData length]];
    NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];
    [request setURL:[NSURL URLWithString:[NSString stringWithFormat:@"http://thewebsite.abc/interface.php"]]];
    [request setHTTPMethod:@"POST"];
    [request setValue:postLength forHTTPHeaderField:@"Content-Length"];
    [request setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"];
    [request setHTTPBody:postData];
    NSURLConnection *conn = [[NSURLConnection alloc]initWithRequest:request delegate:self];
    //return @"";
}

#pragma mark -
#pragma mark NSURLConnection delegates

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData*)data {
    NSLog(@"Success"); // never gets executed
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
    NSLog(@"didFinished");
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
    NSLog(@"FAILED");
}

Answer 1

我怀疑确实没有返回数据（可能是因为某些 Web 服务错误或准备不正确的请求）。

如果您愿意，可以使用Charles 观察请求和响应以确认这一点。顺便说一句，Charles 或任何类似的工具都是添加到您的武器库中的有用武器，因为它极大地简化了 HTTP 问题的诊断，将网络相关问题与客户端编程问题隔离开来。

无论如何，如果您遇到此类错误，您通常会收到服务器返回的非 200 statusCode。见list of HTTP status codes。

您还可以通过实现didReceiveResponse 来验证这一点并检查响应的标头：

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse*)response {
    if ([response isKindOfClass:[NSHTTPURLResponse class]]) {
        int statusCode = [(NSHTTPURLResponse *)response statusCode];
        if (statusCode != 200) {
            NSLog(@"Status code = %ld; response = %@", (long)statusCode, response);

            // handle this error however you'd like
        }
    }

    // temporarily, you might even want to log the whole `response` regardless of the status code
    NSLog(@"%s: %@", __PRETTY_FUNCTION__, response);
}