13

我很好奇，由于 json-framework 的帮助，我目前有一个NSDictionary将一些值设置为对象的地方。NSNull

目的是去除所有NSNull值并将其替换为空字符串。

我确定有人在某个地方做过这个？毫无疑问，它可能是一个四班轮而且很简单，我只是太累了，无法自己解决这个问题。

4

8 回答 8

44

我对 Jacob 的原始答案进行了一些更改，以将其扩展为处理存储在原始字典中的字典和数组。

#import "NSDictionary+NullReplacement.h"
#import "NSArray+NullReplacement.h"

@implementation NSDictionary (NullReplacement)

- (NSDictionary *)dictionaryByReplacingNullsWithBlanks {
    const NSMutableDictionary *replaced = [self mutableCopy];
    const id nul = [NSNull null];
    const NSString *blank = @"";
    
    for (NSString *key in self) {
        id object = [self objectForKey:key];
        if (object == nul) [replaced setObject:blank forKey:key];
        else if ([object isKindOfClass:[NSDictionary class]]) [replaced setObject:[object dictionaryByReplacingNullsWithBlanks] forKey:key];
        else if ([object isKindOfClass:[NSArray class]]) [replaced setObject:[object arrayByReplacingNullsWithBlanks] forKey:key];
    }
    return [NSDictionary dictionaryWithDictionary:[replaced copy]];
}

@end

当然还有一个数组类别：

#import "NSArray+NullReplacement.h"
#import "NSDictionary+NullReplacement.h"

@implementation NSArray (NullReplacement)

- (NSArray *)arrayByReplacingNullsWithBlanks  {
    NSMutableArray *replaced = [self mutableCopy];
    const id nul = [NSNull null];
    const NSString *blank = @"";
    for (int idx = 0; idx < [replaced count]; idx++) {
        id object = [replaced objectAtIndex:idx];
        if (object == nul) [replaced replaceObjectAtIndex:idx withObject:blank];
        else if ([object isKindOfClass:[NSDictionary class]]) [replaced replaceObjectAtIndex:idx withObject:[object dictionaryByReplacingNullsWithBlanks]];
        else if ([object isKindOfClass:[NSArray class]]) [replaced replaceObjectAtIndex:idx withObject:[object arrayByReplacingNullsWithBlanks]];
    }
    return [replaced copy];
}

@end

有了这个，您可以使用任何数组或字典并递归地清除所有 [NSNull null] 实例。

PS为了完整起见，这里是头文件：

@interface NSDictionary (NullReplacement)

- (NSDictionary *)dictionaryByReplacingNullsWithBlanks;

@end

和数组头：

@interface NSArray (NullReplacement)

- (NSArray *)arrayByReplacingNullsWithBlanks;

@end
于 2013-05-22T21:42:27.063 回答
16

真的很简单：

@interface NSDictionary (JRAdditions)
- (NSDictionary *)dictionaryByReplacingNullsWithStrings;
@end

@implementation NSDictionary (JRAdditions)

- (NSDictionary *)dictionaryByReplacingNullsWithStrings {
   const NSMutableDictionary *replaced = [self mutableCopy];
   const id nul = [NSNull null];
   const NSString *blank = @"";

   for(NSString *key in self) {
      const id object = [self objectForKey:key];
      if(object == nul) {
         //pointer comparison is way faster than -isKindOfClass:
         //since [NSNull null] is a singleton, they'll all point to the same
         //location in memory.
         [replaced setObject:blank 
                      forKey:key];
      }
   }

   return [replaced copy];
}

@end

用法：

NSDictionary *someDictThatHasNulls = ...;
NSDictionary *replacedDict = [someDictThatHasNulls dictionaryByReplacingNullsWithStrings];
于 2011-11-10T05:00:01.113 回答
6

在字典中滚动查找 NSNull 是解决问题的一种方法，但我采取了一种稍微懒惰的方法。您可以分配一个空字符串，而不是 nil，但原理是相同的。

CPJSONDictionary.h

@interface NSDictionary (CPJSONDictionary)
- (id)jsonObjectForKey:(id)aKey;
@end

CPJSONDictionary.m

@implementation NSDictionary (CPJSONDictionary)

- (id)jsonObjectForKey:(id)aKey {
    id object = [self objectForKey:aKey];
    if ([object isKindOfClass:[NSNull class]]) {
        object = nil;
    }

    return object;
}

@end
于 2012-11-29T11:57:19.493 回答
4

我已经测试了 Stakenborg 解决方案。它工作得很好，但它有以下问题。例如，如果某个对象预期为数字，则将其转换为NSNull可能是错误的来源。我创建了一种新方法来直接删除NSNull条目。这样你只需要检查对应的密钥是否存在。

加入NSDictionary+NullReplacement

- (NSDictionary *)dictionaryByRemovingNulls{
    const NSMutableDictionary *replaced = [self mutableCopy];
    const id nul = [NSNull null];
    
    for (NSString *key in self) {
        id object = [self objectForKey:key];
        if (object == nul) [replaced removeObjectForKey:key];
        
        else if ([object isKindOfClass:[NSDictionary class]]) [replaced setObject:[object dictionaryByRemovingNulls] forKey:key];
        else if ([object isKindOfClass:[NSArray class]]) [replaced setObject:[object arrayByRemovingNulls] forKey:key];
    }
    return [NSDictionary dictionaryWithDictionary:[replaced copy]];
}

而在NSArray+NullReplacement

- (NSArray *)arrayByRemovingNulls {
    NSMutableArray *replaced = [self mutableCopy];
    const id nul = [NSNull null];

    for (int idx = [replaced count]-1; idx >=0; idx--) {
        id object = [replaced objectAtIndex:idx];
        if (object == nul) [replaced removeObjectAtIndex:idx];
        else if ([object isKindOfClass:[NSDictionary class]]) [replaced replaceObjectAtIndex:idx withObject:[object dictionaryByRemovingNulls]];
        else if ([object isKindOfClass:[NSArray class]]) [replaced replaceObjectAtIndex:idx withObject:[object arrayByRemovingNulls]];
    }
    return [replaced copy];
}
于 2014-04-14T11:11:48.713 回答
3

另一种变化：

NSDictionary * NewDictionaryReplacingNSNullWithEmptyNSString(NSDictionary * dict) {
    NSMutableDictionary * const m = [dict mutableCopy];    
    NSString * const empty = @"";
    id const nul = [NSNull null];
    NSArray * const keys = [m allKeys];
    for (NSUInteger idx = 0, count = [keys count]; idx < count; ++idx) {
        id const key = [keys objectAtIndex:idx];
        id const obj = [m objectForKey:key];
        if (nul == obj) {
            [m setObject:empty forKey:key]; 
        }
    }

    NSDictionary * result = [m copy];
    [m release];
    return result;
}

结果与 Jacob 的结果相同，而且看起来几乎相同，但在我进行的测试中，速度和内存要求是二分之一到三分之一（ARC 或 MRC）。当然，您也可以将其用作类别方法。

于 2011-11-10T05:06:04.067 回答
3

这是我的解决方案：

+ (NSDictionary *)cleanNullInJsonDic:(NSDictionary *)dic
{
    if (!dic || (id)dic == [NSNull null])
    {
        return dic;
    }
    NSMutableDictionary *mulDic = [[NSMutableDictionary alloc] init];
    for (NSString *key in [dic allKeys])
    {
        NSObject *obj = dic[key];
        if (!obj || obj == [NSNull null])
        {
//            [mulDic setObject:[@"" JSONValue] forKey:key];
        }else if ([obj isKindOfClass:[NSDictionary class]])
        {
            [mulDic setObject:[self cleanNullInJsonDic:(NSDictionary *)obj] forKey:key];
        }else if ([obj isKindOfClass:[NSArray class]])
        {
            NSArray *array = [BasicObject cleanNullInJsonArray:(NSArray *)obj];
            [mulDic setObject:array forKey:key];
        }else
        {
            [mulDic setObject:obj forKey:key];
        }
    }
    return mulDic;
}


+ (NSArray *)cleanNullInJsonArray:(NSArray *)array
{
    if (!array || (id)array == [NSNull null])
    {
        return array;
    }
    NSMutableArray *mulArray = [[NSMutableArray alloc] init];
    for (NSObject *obj in array)
    {
        if (!obj || obj == [NSNull null])
        {
//            [mulArray addObject:[@"" JSONValue]];
        }else if ([obj isKindOfClass:[NSDictionary class]])
        {
            NSDictionary *dic = [self cleanNullInJsonDic:(NSDictionary *)obj];
            [mulArray addObject:dic];
        }else if ([obj isKindOfClass:[NSArray class]])
        {
            NSArray *a = [BasicObject cleanNullInJsonArray:(NSArray *)obj];
            [mulArray addObject:a];
        }else
        {
            [mulArray addObject:obj];
        }
    }
    return mulArray;
}
于 2014-05-29T03:02:35.593 回答
2 
-(NSDictionary*)stripNulls:(NSDictionary*)dict{

    NSMutableDictionary *returnDict = [NSMutableDictionary new];
    NSArray *allKeys = [dict allKeys];
    NSArray *allValues = [dict allValues];

    for (int i=0; i<[allValues count]; i++) {
        if([allValues objectAtIndex:i] == (NSString*)[NSNull null]){
            [returnDict setValue:@"" forKey:[allKeys objectAtIndex:i]];
        }
    else
        [returnDict setValue:[allValues objectAtIndex:i] forKey:[allKeys objectAtIndex:i]];
    }

return returnDict;
}
于 2013-07-14T21:35:51.033 回答
0

nsnull 上返回 nil 的类别似乎也有意义，至少对我而言。那里有几个。一个使所有调用都返回 nil，这似乎是有道理的。抱歉没有链接。我想如果您以后需要使用 nspropertylistserialization 该类别可能不适合您。

于 2013-09-28T12:50:15.153 回答