Question

我来自JSON

[{ “照片”：空}]

我使用此代码

NSMutableArray *jPhoto = [NSMutableArray arrayWithArray:(NSArray *)[jsonDict valueForKey:@"photo"]];

如果我想使用if（），我如何检查它？

修改

这里是JSON数据

   [{"photo":
              [{"image":"http:\/\/www.yohyeh.com\/upload\/shisetsu\/13157\/photo\/1304928459.jpg","title":"test picture","content":"this is description for test picture.\r\n\u8aac\u660e\u6587\u306a\u306e\u306b\u30fb\u30fb\u30fb\u30fb\u30fb\u30fb\u30fb\u30fb\u30fb\u30fb\u30fb\u30fb"}
              ,{"image":"http:\/\/www.yohyeh.com\/upload\/shisetsu\/13157\/photo\/1304928115.jpg","title":"nothing","content":"iMirai"}
              ,{"image":"http:\/\/www.yohyeh.com\/upload\/shisetsu\/13157\/photo\/1303276769.jpg","title":"iMirai","content":"Staff"}]}
  ]

这是我的JSON解析器

NSError *theError = nil;     
    NSString *URL = [NSString stringWithFormat:@"http://www.yohyeh.com/apps/get_sub_detail.php?id=%@&menu=photo",g_id];
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:URL]];
    NSURLResponse *theResponse =[[[NSURLResponse alloc]init] autorelease];
    NSData *data = [NSURLConnection sendSynchronousRequest:request returningResponse:&theResponse error:&theError];   
    NSMutableString *string = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];

    NSDictionary *jsonDict = [string JSONValue];

感谢您的帮助

Answer 1

我相信大多数JSON解析器将null表示为[NSNull null]。

考虑到jsonDict指向数组中的单个元素，则以下内容应该起作用：

if ([jsonDict objectForKey:@"photo"] == [NSNull null]) {
    // it's null
}

根据评论进行修改：所以jsonDict，尽管它的名字，是一个数组。在这种情况下，请将jsonDict重命名为jsonArray以避免进一步混淆。然后，考虑jsonArray指向类似于问题中发布的示例的数组：

NSArray *photos = [jsonArray valueForKey:@"photo"];
for (id photo in photos) {
    if (photo == [NSNull null]) {
        // photo is null
    }
    else {
        // photo isn't null
    }
}

根据OP的修改问题进一步修改：

NSArray *jsonArray = [string JSONValue];

NSArray *photos = [jsonArray valueForKey:@"photo"];
for (id photo in photos) {
    if (photo == [NSNull null]) {
        // photo is null
    }
    else {
        // photo isn't null. It's an array
        NSArray *innerPhotos = photo;
        …
    }
}

Answer 2

如果有效负载是具有可能值的复杂JSON结构，则宏可能会有所帮助。

#define SET_IF_NOT_NULL(TARGET, VAL) if(VAL != [NSNull null]) { TARGET = VAL; }

和宏可以像

一样引用

SET_IF_NOT_NULL(myRecord.name, [jsonData objectForKey:@"name"]);

Answer 3

没有简单的方法可以解决这个问题，但我这样做的方法是在NSObject上创建一个类别：

@interface NSObject (NotNull)

- (instancetype)notNull;

@end

如此实施：

@implementation NSObject (NotNull)

- (instancetype)notNull
{
    return self;
}

@end

@implementation NSNull (NotNull)

- (instancetype)notNull
{
    return nil;
}

@end

然后您可以将notNull发送到JSON字典中的任何可选对象，然后您将获得nil 回来，如果它是NSNull。否则你会得到原始对象。例如：

self.parentIdentifier = [dictionary[@"parent_id"] notNull];

Answer 4

尝试检查[jPhoto count]或[NSNull null]

Answer 5

希望这会有所帮助。

- （NSMutableDictionary *）jsonCheckforNull：（NSMutableDictionary *）json {

NSMutableDictionary * strongjson = [json mutableCopy];

public class RelayCommand : ICommand
{
    readonly Action<object> _execute;
    readonly Predicate<object> _canExecute;

    public RelayCommand(Action<object> execute)
        : this(execute, null)
    {
    }

    public RelayCommand(Action<object> execute, Predicate<object> canExecute)
    {
        if (execute == null)
            throw new ArgumentNullException(nameof(execute));

        _execute = execute;
        _canExecute = canExecute;
    }

    [DebuggerStepThrough]
    public bool CanExecute(object parameter)
    {
        return _canExecute == null ? true : _canExecute(parameter);
    }

    public event EventHandler CanExecuteChanged
    {
        add { CommandManager.RequerySuggested += value; }
        remove { CommandManager.RequerySuggested -= value; }
    }

    public void Execute(object parameter)
    {
        _execute(parameter);
    }
}

}

- （NSMutableArray *）ArrayCheckforNull：（NSMutableArray *）arr {

for (NSString *ktr in json) {

    NSObject *str=[json objectForKey:ktr];

    if ([str isKindOfClass:[NSArray class]]) {
        if (!(str==[NSNull null])) {
            NSArray *temp = [json allKeysForObject:str];
            str=[[self ArrayCheckforNull:(NSMutableArray*)str]mutableCopy];
            NSString *key = [temp objectAtIndex:0];
            [strongjson removeObjectForKey:key];
            [strongjson setObject:str forKey:key];
        }
        else
        {
            NSArray *temp = [strongjson allKeysForObject:str];
            NSString *key = [temp objectAtIndex:0];
            [strongjson removeObjectForKey:key];
            [strongjson setObject:@"-----" forKey:key];
        }

    }
    else if ([str isKindOfClass:[NSDictionary class]]) {
        if (!(str==[NSNull null])) {
            str=[[self jsonCheckforNull:str]mutableCopy];
            NSArray *temp = [strongjson allKeysForObject:str];
            NSString *key = [temp objectAtIndex:0];
            [strongjson removeObjectForKey:key];
            [strongjson setObject:str forKey:key];
        }
        else
        {
            NSArray *temp = [strongjson allKeysForObject:str];
            NSString *key = [temp objectAtIndex:0];
            [strongjson removeObjectForKey:key];
            [strongjson setObject:@"-----" forKey:key];
        }

    }

    else {

        if (str ==[NSNull null]) {
            NSArray *temp = [strongjson allKeysForObject:str];
            NSString *key = [temp objectAtIndex:0];
            [strongjson removeObjectForKey:key];
            [strongjson setObject:@"----" forKey:key];
        }

    }

}
return strongjson;

}

如何检查如果我从json得到null？

5 个答案: