iphone - 使用 SBJSON 进行 JSON 解析和检查

Question

我有这个 JSON:

{
    "errors": [
    ], 
    "warnings": [
    ], 
    "data": {
        "token": "someToken"
    }, 
    "page": {
        "current": 1, 
        "total": 1
    }
}

我正在尝试使用 SBJSON 解析 token 。解析没有问题。但是，在某些情况下，检索到的 JSON 没有标记值。我如何检查该值是否存在，因为如果我不检查我的应用程序会因 EXCBadAccess 而崩溃。

谢谢!

Answer 1

SBJSON 会返回一个 NSDictionary 对象。您只需要检查 objectForKey 返回的指针是否为 nil，还要检查它是否为 NSNull(如果该值存在，但在 JSON 中设置为 null，则会出现这种情况)，您还可以确保数据实际上是一个 NSDictionary:

id dataDictionaryId = [resultsDictionary objectForKey:@"data"];

// check that it isn't null ... this will be the case if the
// data key value pair is not present in the JSON
if (!dataDictionaryId) 
{
    // no data .. do something else
    return;
}

// then you need to check for the case where the data key is in the JSON
// but set to null. This will return you a valid NSNull object. You just need 
// ask the id that you got back what class it is and compare it to NSNull
if ([dataDictionaryId isKindOfClass:[NSNull class]])
{
    // no data .. do something else
    return;
}

// you can even check to make sure it is actually a dictionary
if (![dataDictionaryId isKindOfClass:[NSDictionary class]])
{
    // you got a data thing, but it isn't a dictionary?
    return;
}

// yay ... it is a dictionary
NSDictionary * dataDictionary = (NSDictionary*)dataDictionaryId;

// similarly here you could check to make sure that the token exists, is not null
// and is actually a NSString ... but for this snippet, lets assume it is
NSString * token = [dataDictionary objectForKey:@"token"];
if (!token)
    // no token ... do something else

更新

这是我为了检查SBJSON解析结果而写的测试代码:

NSError* error = NULL;
id json = [parser objectWithString:@"{\"data\":null}" error:&error];
NSDictionary * results = (NSDictionary*)json;
id dataDictionaryId = [results objectForKey:@"data"];
if (!dataDictionaryId || [dataDictionaryId isKindOfClass:[NSNull class]])
    return NO;