当需要XML时，NSURLConnection返回null

Question

我有一个basecamp帐户，我正试图通过它的XML API访问它。

我已经创建了一个具有正确报头字段的NSURL请求。

    NSURL* projectsUrl = [NSURL URLWithString:[self.accountURL stringByAppendingString:@"/projects.xml"]];
    NSMutableURLRequest* projectsRequest = [NSMutableURLRequest requestWithURL:projectsUrl];

    [projectsRequest setValue:@"application/xml" forHTTPHeaderField:@"Content-Type"];
    [projectsRequest setValue:@"application/xml" forHTTPHeaderField:@"Accept"];

我创建了一个连接并启动它。

    NSURLConnection* connection = [[NSURLConnection alloc] initWithRequest:projectsRequest delegate:self];
    [connection start];
    [connection autorelease];

Basecamp使用HTTP基本身份验证。所以我使用一个NSCredential对象来处理它，如下所示。

-(void) connection:(NSURLConnection*)connection didReceiveAuthenticationChallenge:(NSURLAuthenticationChallenge*)authenticationChallenge
{


    if ([authenticationChallenge previousFailureCount] <=2 ) {
        NSURLCredential* basecampCredentials;
        basecampCredentials = [NSURLCredential credentialWithUser:[self username] 
                                                         password:[self password]
                                                      persistence:NSURLCredentialPersistenceNone];
        [[authenticationChallenge sender] useCredential:basecampCredentials forAuthenticationChallenge:authenticationChallenge];
    }else {
        [[authenticationChallenge sender] cancelAuthenticationChallenge:authenticationChallenge];

    }

}

当我从connection接收数据时，我用这些委托来处理它。

-(void) connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    [[self responseData] appendData: data];
    NSLog(@"I received %@", [self responseData]);

}


-(void) connectionDidFinishLoading:(NSURLConnection*)connection
{
    NSLog(@"I FINALLY received %@", [self responseData]);

    NSXMLParser* parser = [[NSXMLParser alloc] initWithData:[self responseData]];
    [parser setDelegate:self];
    BOOL success = [parser parse];
    if (success) {
        NSLog(@"XML parse success");
    }else {
        NSLog(@"XML parse ERROR");
    }

    [parser autorelease];

}

问题是，即使在使用正确的url、身份验证凭据和报头字段之后，我也会在responseData中获得null数据，而当我尝试使用curl访问相同的url时，我会从basecamp服务器获得正确的xml响应。我是目标C的新手。请解释并告诉我我还应该设置什么才能正确完成这项任务。

Answer 1

在启动连接([connection start];)之前，您应该初始化属性responseData，例如self.responseData = [[NSMutableData alloc] init];。

在方法- (void)connection:(NSURLConnection *)conn didReceiveResponse:(NSURLResponse *)response中，您应该将该数据的长度设置为零：[self.responseData setLength:0];

Answer 2

您确定设置了[self responseData]吗

Answer 3

使用ASIHTTPRequest尝试相同的URL，看看是否有效。