使用 NSURLSession 获取 JSON 数据

Question

我正在尝试使用 NSURLSession 从 google distance api 获取数据，但如下所示，当我打印响应和数据时，我得到的结果为 NULL。 可能是什么问题？或者有没有其他更好的方式来获取 JSON 数据。

NSString *urlAsString = [NSString stringWithFormat:@"https://maps.googleapis.com/maps/api/distancematrix/json?origins=Vancouver+BC|Seattle&destinations=San+Francisco|Victoria+BC&mode=bicycling&language=fr-FR&key=API-KEY"];

NSURL *url = [NSURL URLWithString:urlAsString];


NSURLSession *session = [NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration]];

[[session dataTaskWithURL:[NSURL URLWithString:urlAsString]
            completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {

                NSLog(@"RESPONSE: %@",response);
                NSLog(@"DATA: %@",data);


            }] resume];

Answer 1

你应该在你的 url 字符串上使用stringByAddingPercentEscapesUsingEncoding:，这就是你没有得到响应的原因：服务器返回了一个错误。

您应该检查过error ;)

我在 URL 字符串中替换了您的 API 密钥，如果您复制/粘贴我的代码，请记住输入您自己的 :)

NSString *urlAsString = [NSString stringWithFormat:@"https://maps.googleapis.com/maps/api/distancematrix/json?origins=Vancouver+BC|Seattle&destinations=San+Francisco|Victoria+BC&mode=bicycling&language=fr-FR&key=YOUR-API-KEY"];

NSCharacterSet *set = [NSCharacterSet URLQueryAllowedCharacterSet];
NSString *encodedUrlAsString = [urlAsString stringByAddingPercentEncodingWithAllowedCharacters:set];

NSURLSession *session = [NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration]];

[[session dataTaskWithURL:[NSURL URLWithString:encodedUrlAsString]
        completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {

    NSLog(@"RESPONSE: %@",response);
    NSLog(@"DATA: %@",data);

    if (!error) {
        // Success
        if ([response isKindOfClass:[NSHTTPURLResponse class]]) {
            NSError *jsonError;
            NSDictionary *jsonResponse = [NSJSONSerialization JSONObjectWithData:data options:0 error:&jsonError];

            if (jsonError) {
                // Error Parsing JSON

            } else {
                // Success Parsing JSON
                // Log NSDictionary response:
                NSLog(@"%@",jsonResponse);
            }
        }  else {
            //Web server is returning an error
        }
    } else {
        // Fail
        NSLog(@"error : %@", error.description);
    }
}] resume];

Answer 2

如果您打印出错误参数中返回的内容，您可能会得到一个非常好的提示。

IE：

NSString *unencodedURLString = [NSString stringWithFormat:@"https://maps.googleapis.com/maps/api/distancematrix/json?origins=Vancouver+BC|Seattle&destinations=San+Francisco|Victoria+BC&mode=bicycling&language=fr-FR&key=API-KEY"];
NSString *encodedURLString = (NSString *)CFURLCreateStringByAddingPercentEscapes(
                        NULL,
                        (CFStringRef)unencodedURLString,
                        NULL,
                        (CFStringRef)@"!*'();:@&=+$,/?%#[]",
                        kCFStringEncodingUTF8 );

[[session dataTaskWithURL:[NSURL URLWithString:encodedURLString]
            completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {

    if (error != nil)
    {
       // if there's an error, print it out...
       NSLog(@"error in NSURLSession is %@", [error localizedDescription]);
    } else {
       NSLog(@"RESPONSE: %@",response);
       NSLog(@"DATA: %@",data);
    }
}] resume];

我正在使用的 URL 编码例程 is found here。

Answer 3

来自文档：

网址必须采用以下格式：

https://maps.googleapis.com/maps/api/distancematrix/json?origins=Vancouver+BC|Seattle&destinations=San+Francisco|Victoria+BC&key=YOUR_API_KEY

您正在请求：

origins: Vancouver+BC|Seattle
destinations: San+Francisco|Victoria+BC
mode: driving
key: API_KEY

过境：

https://maps.googleapis.com/maps/api/distancematrix/json?origins=Vancouver+BC|Seattle&destinations=San+Francisco|Victoria+BC&mode=transit&transit_mode=train&key=YOUR_API_KEY

您要求：

  origins: Vancouver+BC|Seattle
destinations: San+Francisco|Victoria+BC
mode: transit
transit_mode: train
key: API_KEY