Question

我需要对URL进行HTTPRequest并解析生成的JSON，我尝试了以下代码

- (void)viewDidLoad {
    [super viewDidLoad];
    NSLog(@"viewdidload");
    self.responseData = [NSMutableData data];
    NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:@"http://www.gcap.eu/omosanya/download.php"]];
    [[NSURLConnection alloc] initWithRequest:request delegate:self];
}

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
    NSLog(@"didReceiveResponse");
    [self.responseData setLength:0];
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
    [self.responseData appendData:data];
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
    NSLog(@"didFailWithError");
    NSLog([NSString stringWithFormat:@"Connection failed: %@", [error description]]);
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
    NSLog(@"connectionDidFinishLoading");
    NSLog(@"Succeeded! Received %lu bytes of data",(unsigned long)[self.responseData length]);

    // convert to JSON
    NSError *myError = nil;
    NSDictionary *res = [NSJSONSerialization JSONObjectWithData:_responseData options:NSJSONReadingAllowFragments error:&myError];

    // show all values
    for(id key in res) {
        id value = [res objectForKey:key];

        NSString *keyAsString = (NSString *)key;
        NSString *valueAsString = (NSString *)value;

        NSLog(@"key: %@", keyAsString);
        NSLog(@"value: %@", valueAsString);
    }

    // extract specific value...
    NSArray *results = [res objectForKey:@"results"];

    for (NSDictionary *result in results) {
        NSString *icon = [result objectForKey:@"timestamp"];
        NSLog(@"icon: %@", icon);
    }

}

我在控制台中收到以下输出：

2015-02-03 17:12:28.201 LSDir[1495:130391] viewdidload
2015-02-03 17:12:28.831 LSDir[1495:130391] didReceiveResponse
2015-02-03 17:12:36.815 LSDir[1495:130391] connectionDidFinishLoading
2015-02-03 17:12:36.815 LSDir[1495:130391] Succeeded! Received 8223702 bytes of data

请注意，没有打印JSON？为什么这样，我该如何解决？我的NSJSONSerialization有什么问题吗？

Answer 1

请注意json字符串可以是字典或数组。如果你不确定json字符串是哪种，你必须在采取行动之前验证它。这是验证json对象的代码

id jsonObject = [NSJSONSerialization JSONObjectWithData:_responseData options:NSJSONReadingAllowFragments error:&myError];
if ([jsonObject isKindOfClass:[NSArray class]]) {
    NSLog(@"its an array!");
    NSArray *jsonArray = (NSArray *)jsonObject;
    //do your work with this array
}
else {
    NSLog(@"its probably a dictionary");
    NSDictionary *jsonDictionary = (NSDictionary *)jsonObject;
    //do your work with this dictionary
}

Answer 2

请勿使用NSURLConnection - 请改用基于块的NSURLSession API。它是NSURLConnection的后继者，向后兼容iOS 7。

以下是解决问题所需的代码片段（我认为）：

    NSURLSession *session = [NSURLSession sharedSession];
    NSURLSessionDataTask *task = [session dataTaskWithURL:[NSURL URLWithString:@"http://www.gcap.eu/omosanya/download.php"]
                                         completionHandler:^(NSData *data,
                                                             NSURLResponse *response,
                                                             NSError *error) {

                                             NSError *deserializationError = nil;
                                             if (!error) { // HTTP Reqeust Succeeded
                                                 id results = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingAllowFragments error:&deserializationError];

                                                 if (!deserializationError) { // Deserialization Succeeded
                                                     if ([results isKindOfClass:[NSDictionary class]]) { // Dictionary
                                                         NSLog(@"JSON Dictionary Data %@", (NSDictionary *)results);
                                                     } else { // Array
                                                         NSLog(@"JSON Array Data %@", (NSArray *)results);
                                                     }
                                                 } else { // Deserialization Failed
                                                     NSLog(@"Deserializaiton Error: %@", error);
                                                 }
                                             } else { // HTTP Request Failed
                                                 NSLog(@"HTTP Error: %@", error);
                                             }}];
   [task resume];

NSURLSession上有一个很棒的（免费）教程：http://www.raywenderlich.com/51127/nsurlsession-tutorial

Answer 3

我试过了：

-(void)viewDidAppear:(BOOL)animated
{             
        dispatch_async(kBgQueue, ^{
                NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:@"http://www.gcap.eu/omosanya/download.php"]];
                [self performSelectorOnMainThread:@selector(receivedCall:)withObject:data waitUntilDone:YES];
        });
}
- (void) receivedCall:(NSData *)response
{
        NSError *error;

        NSArray *parsedResponse = [NSJSONSerialization
                                        JSONObjectWithData:response
                                        options:NSJSONReadingMutableContainers
                                        error:&error];

        if (error) {
                NSLog(@"Error %@", error);
        }
        NSLog(@"Silly Response %@", parsedResponse);

}

其中：

#define kBgQueue dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)

我收到以下错误：

Error Domain=NSCocoaErrorDomain Code=3840 "The operation couldn’t be completed. (Cocoa error 3840.)" (Badly formed array around character 3482608.) UserInfo=0x16512920 {NSDebugDescription=Badly formed array around character 3482608.}

我怀疑问题是JSON格式错误，可以通过调查服务器如何形成JSON来解决问题。

此外，上面的代码可能值得使用 - 它不会阻塞主线程并使用更少的代码实现相同的功能。它也更容易扩展，因为如果您想要并行或顺序进行多个API调用，这可以比您使用的方法更容易实现。

iOS中的JSON调用不接收数据但不能解析或记录它

3 个答案: