NSData *res = request.responseData;
NSError *error;
NSDictionary *json = [NSJSONSerialization JSONObjectWithData:res options:NSJSONReadingMutableLeaves error:&error];
if (error) {
        NSLog(@"%@",error);

}

關於引數：options

NSJSONReadingMutableContainers：Specifies that arrays and dictionaries are created as mutable objects.
返回的容器是可變型別的（Array和Dictionary） NSJSONReadingMutableLeaves： Specifies that leaf strings in the JSON object graph are created as instances of NSMutableString.
返回的葉子NSString是可變型別的； NSJSONReadingAllowFragments： Specifies that the parser should allow top-level objects that are not an instance of NSArray or NSDictionary. 允許頂層的介面不是NSArray或NSDictionary； 如果都不需要，預設填0。

範例

1. 同步方式：

url = [NSString stringWithFormat:@"http://192.168.1.24/netoffice/passwordcheck.jsp?Account=%@&Password=%@&rand=%@", username, password, randcode];
    request = [[NSMutableURLRequest alloc] initWithURL:[NSURL URLWithString:url] cachePolicy:NSURLCacheStorageAllowed timeoutInterval:10];
NSData *responseData = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error];


if (responseData) {
                    … … 
}

  2. 非同步方式1：

[NSURLConnection sendAsynchronousRequest:hotWordsRequest queue:operationQueue completionHandler:^(NSURLResponse *response, NSData *data, NSError *error) {
if (error) {
		NSLog(@"error:\n%@",error);
                return;
}
           NSDictionary *json = [NSJSONSerializationJSONObjectWithData:data options:0error:&error];
NSLog(@"%@",json);
        }];

 3. 非同步方式2：

    1.建立NSConnection物件，設定委託物件
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:[self urlString]]];
[NSURLConnection connectionWithRequest:request delegate:self];          

2. NSURLConnection delegate委託方法                             

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response; 
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error; 
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data; 
- (void)connectionDidFinishLoading:(NSURLConnection *)connection; 
 
3. 實現委託方法
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
// store data
[self.receivedData setLength:0];      //通常在這裡先清空接受資料的快取
}
  
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
[self.receivedData appendData:data];    //可能多次收到資料，把新的資料新增在現有資料最後
}
 
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
		// 錯誤處理
	}     
 
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
// disconnect
[UIApplication sharedApplication].networkActivityIndicatorVisible = NO;  
NSString *returnString = [[NSString alloc] initWithData:self.receivedData encoding:NSUTF8StringEncoding];     
NSLog(returnString);
[self urlLoaded:[self urlString] data:self.receivedData];
firstTimeDownloaded = YES;
}

3.ASIHTTPRequest的使用：

   - (void)getSearchHotWordsFromSender:(PSearchViewController *) searchViewController{
              NSURL *url = [NSURLURLWithString:PaperSearchHotWordsUrl];
              ASIHTTPRequest *hotWordsRequest = [ASIHTTPRequestrequestWithURL:url];
              self.currentConnectionRequest = hotWordsRequest;
    
              [hotWordsRequest setDelegate:searchViewController];
              [hotWordsRequest setDidFinishSelector:@selector(hotWordsRequestFinished:)];
              [hotWordsRequest setDidFailSelector:@selector(hotWordsRequestFailed:)];
    
              [hotWordsRequest setRequestMethod:@"GET"];
    
              //設定超時時間
              [hotWordsRequest setTimeOutSeconds:ConnectionTimeOutSeconds];
              //保持cookie的狀態
              //[hotWordsRequest setUseCookiePersistence:NO];
              //發出非同步請求
              [hotWordsRequest startAsynchronous];


                    }
          回撥處理：



     
     - (void)hotWordsRequestFinished:(ASIHTTPRequest *)request{
    
         NSError *error;
         NSDictionary *json = [NSJSONSerializationJSONObjectWithData:request.responseDataoptions:0error:&error];
    
         if (error) {
             NSLog(@"%@",error);


                   }
               … ...
     }
     - (void)hotWordsRequestFailed:(ASIHTTPRequest *)request{
       … … 


     }

////////////////------------------------------------------------------

//1.建立post方式的 引數字串url

+(NSString *)createPostURL:(NSMutableDictionary *)params

{

    NSString *postString=@"";

    for(NSString *key in [params allKeys])

    {

        NSString *value=[params objectForKey:key];

        postString=[postString stringByAppendingFormat:@"%@=%@&",key,value];

    }

    if([postString length]>1)

    {

        postString=[postString substringToIndex:[postString length]-1];

    }

    return postString;

}

//2.zwh -自定義的通用方法－－－－－－post資料回伺服器，並返回結果資料集

+(NSData *)getResultDataByPost:(NSMutableDictionary *)params

{

    NSString *postURL=[Utility createPostURL:params];

    NSError *error;

    NSURLResponse *theResponse;

NSMutableURLRequest *theRequest=[NSMutableURLRequestrequestWithURL:[NSURLURLWithString:BASEURL]];

    [theRequest setHTTPMethod:@"POST"];

    [theRequest setHTTPBody:[postURL dataUsingEncoding:NSUTF8StringEncoding]];

    [theRequest addValue:@"application/x-www-form-urlencoded"forHTTPHeaderField:@"Content-Type"];

return [NSURLConnectionsendSynchronousRequest:theRequest returningResponse:&theResponse error:&error];

}

 ／／呼叫例項程式碼

NSMutableDictionary *params=[[NSMutableDictionaryalloc] init];

    [params setObject:@"taobao.taobaoke.items.get"forKey:@"method"];

    [params setObject:@"num_iid,title,pic_url,price,score"forKey:@"fields"];

    [params setObject:@"淘寶帳戶" forKey:@"nick"];

    [params setObject:selectedItemCat.cid forKey:@"cid"];

    [params setObject:@"true"forKey:@"is_mobile"];

    NSData *resultData=[Utility getResultData:params];