iOS使用NSURLConnection发送同步和异步HTTP Request

1. 同步发送

- (NSString *)sendRequestSync
{
    // 初始化请求, 这里是变长的, 方便扩展
    NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];

    // 设置
    [request setURL:[NSURL URLWithString:urlStr]];
    [request setHTTPMethod:@"POST"];
    [request setValue:host forHTTPHeaderField:@"Host"];
    NSString *contentLength = [NSString stringWithFormat:@"%d", [content length]];
    [request setValue:contentLength forHTTPHeaderField:@"Content-Length"];
    [request setHTTPBody:content];

    // 发送同步请求, data就是返回的数据
    NSError *error = nil;
    NSData *data = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:&error];
    if (data == nil) {
        NSLog(@"send request failed: %@", error);
        return nil;
    }

    NSString *response = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
    NSLog(@"response: %@", response);
    return response;
}

2.异步发送

1) 使用delegate的方式:

- (void)sendRequestAsync
{
    // 初始化请求
    NSMutableURLRequest  *request = [[NSMutableURLRequest alloc] init];

    // 设置
    [request setURL:[NSURL URLWithString:urlStr]];
    [request setCachePolicy:NSURLRequestUseProtocolCachePolicy]; // 设置缓存策略
    [request setTimeoutInterval:5.0]; // 设置超时

    //......

    receivedData = [[NSMutableData alloc] initData: nil];

    NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request     delegate:self];
    if (connection == nil) {
        // 创建失败
        return;
    }
}

异步发送使用代理的方式, 需要实现以下delegate接口:

// 收到回应
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    NSLog(@"receive the response");
    // 注意这里将NSURLResponse对象转换成NSHTTPURLResponse对象才能去
    NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse*)response;
    if ([response respondsToSelector:@selector(allHeaderFields)]) {
        NSDictionary *dictionary = [httpResponse allHeaderFields];
        NSLog(@"allHeaderFields: %@",dictionary);
    }
    [receivedData setLength:];
}    

// 接收数据
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    NSLog(@"get some data");
    [receivedData appendData:data];
}

// 数据接收完毕
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    NSString *results = [[NSString alloc]
                         initWithBytes:[receivedData bytes]
                         length:[receivedData length]
                         encoding:NSUTF8StringEncoding];

    NSLog(@"connectionDidFinishLoading: %@",results);
}

// 返回错误
-(void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
    NSLog(@"Connection failed: %@", error);
}    

2) iOS 5.0版本新增异步发送接口:

+ (void)sendAsynchronousRequest:(NSURLRequest *)request
                          queue:(NSOperationQueue*) queue
              completionHandler:(void (^)(NSURLResponse*, NSData*, NSError*)) handlerNS_AVAILABLE(10_7, 5_0);