Question

我有一个非常简单的问题，我想有经验的人很容易回答。有一个JSON提要，可以将视频URL内容提供给我正在构建的其中一个应用程序。它看起来像这样：

    {
    "playlist": [
        {
            "videos": {
                "ds900": {
                    "length": 30,
                    "bitrate": "900",
                    "uri": "http://somevideo1.mp4"
                },
                "ds300": {
                    "length": 30,
                    "bitrate": "300",
                    "uri": "http://somevideo2.mp4"
                },
                "ds500": {
                    "length": 30,
                    "bitrate": "500",
                    "uri": "http://somevideo3.mp4"
                },
                "ds700": {
                    "length": 30,
                    "bitrate": "700",
                    "uri": "http://somevideo4.mp4"
                }
            }
        }
    ],
    "playlistName": "The Play List Name",
    "description": "The description"
}

要反序列化，我有以下代码：

    -(void)connectToVideoLink
{
    NSString *urlString = @"http://Link_To_JSON_feed";
    NSURL *url = [NSURL URLWithString:urlString];

    NSURLRequest *urlRequest =
    [NSURLRequest requestWithURL:url
                     cachePolicy:NSURLRequestReloadIgnoringLocalAndRemoteCacheData
                 timeoutInterval:30.0f];


    NSOperationQueue *queue =[[NSOperationQueue alloc] init];

    [NSURLConnection sendAsynchronousRequest:urlRequest
                                       queue:queue
                           completionHandler:^(NSURLResponse *response,
                                               NSData *dataR,
                                               NSError *error) {

                               if([dataR length]>0 && error == nil)
                               {
                                   NSString *feed = [[NSString alloc] initWithData:dataR
                                                                          encoding:NSUTF8StringEncoding];
                                   [self trythis2:dataR];

                               }
                               else if ([dataR length]==0 && error==nil)
                               {
                                   NSLog(@"Nothing available");
                               }
                               else if (error != nil)
                               {
                                   NSLog(@"Error is : %@", error);
                               }

     }]; 
}

然后调用函数[self trythis2：dataR];这将调用反序列化方法。

-(void)trythis2:(NSData*)responseData
{
    NSError *e = nil;

    id jsonObject = [NSJSONSerialization JSONObjectWithData:responseData options:NSJSONReadingMutableContainers error:&e];

    NSDictionary *jsonArray = (NSDictionary *)jsonObject;
    jsonArray = [NSJSONSerialization JSONObjectWithData: responseData options: NSJSONReadingAllowFragments error: &e];
    //NSArray
    if (!jsonArray) {
        NSLog(@"Error parsing JSON: %@", e);
    } else {

        NSArray *playlistdict = [jsonArray objectForKey:@"playlist"];
        for (NSDictionary *playlistitems in playlistdict) {
            NSDictionary *videoTypes = [[playlistitems objectForKey:@"videos"] objectForKey:@"ds700"];
            NSLog(@"String: %@", videoTypes);
            for (NSDictionary *videoTypesItems in videoTypes) {
                NSLog(@"ds700 Key: %@", videoTypesItems);

                NSLog(@"Val : %@",[videoTypesItems objectForKey:@"uri"]); //error caused here


            }
        }
    }
}

如上所述，错误在注释行处停止。这是我的输出：

2013-08-07 15:21:22.711 DeserializeJSON[3025:1d03] String: {
    bitrate = 700;
    length = 30;
    uri = "http://somevideo1.mp4";
}
2013-08-07 15:21:22.713 DeserializeJSON[3025:1d03] ds700 Key: bitrate
2013-08-07 15:21:22.714 DeserializeJSON[3025:1d03] -[__NSCFString objectForKey:]: unrecognized selector sent to instance 0x1ed3e910
2013-08-07 15:21:22.715 DeserializeJSON[3025:1d03] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFString objectForKey:]: unrecognized selector sent to instance 0x1ed3e910'
*** First throw call stack:
(0x33e853e7 0x3bb80963 0x33e88f31 0x33e8764d 0x33ddf208 0x72ee9 0x71fa3 0x3471c229 0x34713a89 0x3478bfe7 0x3bf9a793 0x3bf9e657 0x3bf9e7d9 0x3bfc27f1 0x3bfc2684)
libc++abi.dylib: terminate called throwing an exception
(lldb)

我确定uri =“http://somevideo1.mp4”;是可用的，但你可以看到我无法抓住它。我尝试使用NSString变量并尝试在记录之前为其分配[videoTypesItems objectForKey：@“uri”]，但这也无效。解析这个JSON我在哪里出错了？谢谢你的阅读。

Answer 1

您的videoTypes字典没有任何嵌套数据。你想要这样的东西：

NSDictionary *videoTypes = [[playlistitems objectForKey:@"videos"] objectForKey:@"ds700"];
NSString *url = videoTypes[@"uri"];
NSLog(@"Val: %@", uri);

如果你真的想迭代字典的键，你可以这样做：

NSDictionary *videoTypes = [[playlistitems objectForKey:@"videos"] objectForKey:@"ds700"];
NSLog(@"String: %@", videoTypes);
for (NSString *videoTypeKey in [videoTypes allKeys]) {
    NSLog(@"ds700 Key: %@", videoTypeKey);

    NSLog(@"Val : %@", videoTypesItems[videoTypeKey]); //error caused here
}

Answer 2

    NSDictionary *videoTypes = [[playlistitems objectForKey:@"videos"] objectForKey:@"ds700"];
    NSLog(@"String: %@", videoTypes);
    for (NSDictionary *videoTypesItems in videoTypes) {
        NSLog(@"ds700 Key: %@", videoTypesItems);

        NSLog(@"Val : %@",[videoTypesItems objectForKey:@"uri"]); //error caused here


    }

在videoTypes中，您正在打开“ds700”字典。这不包含任何子词典，只包含键值对。然而，你的for循环正在创建一个NSDictionary。

    "ds700": {
        "length": 30,
        "bitrate": "700",
        "uri": "http://somevideo4.mp4"
    }

如果您想循环浏览所有不同的视频类型（ds300，ds500，ds700和ds900），请尝试以下操作：

    NSDictionary *videoTypes = [[playlistitems objectForKey:@"videos"];
    NSLog(@"String: %@", videoTypes);
    for (NSDictionary *videoTypesItems in videoTypes) {
        NSLog(@"type Key: %@", videoTypesItems);

        NSLog(@"Val : %@",[videoTypesItems objectForKey:@"uri"]);


    }

使用NSJSONSerialization正确反序列化嵌套的JSON源？

2 个答案: