Question

我很好奇，我目前有一个NSDictionary，其中一些值设置为NSNull对象，这得益于json-framework的帮助。

目标是去除所有NSNull值并将其替换为空字符串。

我确定有人在某处做过这件事吗？毫无疑问，它可能只是一个四线，而且很简单，我只是太过刻不知所措了。

谢谢！

Answer 1

我对Jacob的原始答案进行了一些更改，以扩展它以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，你可以获取任何数组或字典，并递归地消灭所有[NSNull null]实例。

希望它有所帮助。

布兰登

P.S。为了完成起见，这里是头文件：

@interface NSDictionary (NullReplacement)

- (NSDictionary *)dictionaryByReplacingNullsWithBlanks;

@end

数组头：

@interface NSArray (NullReplacement)

- (NSArray *)arrayByReplacingNullsWithBlanks;

@end

Answer 2

非常简单：

@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];

Answer 3

翻阅字典寻找NSNull是解决问题的一种方法，但我采取了一种稍微懒散的方法。你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

Answer 4

我测试了Stakenborg解决方案。它运作良好，但它有以下问题。例如，如果某个对象是数字，则将其转换为NSNull可能是错误的来源。我创建了一个新方法来直接删除NSNull条目。这样，您只需检查是否存在对应密钥。

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]];
}

并在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];
}

我希望这会有所帮助

Answer 5

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;
}

结果与之相同，并且看起来与雅各布非常相似，但在我做的测试中，速度和内存要求是半个到三分之一（ARC或MRC）。当然，您也可以将它用作类别方法。

Answer 6

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;
}

Answer 7

-(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;
}

Answer 8

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。一个让所有的呼叫返回零，这似乎是有道理的。对不起没有链接。我想如果你以后需要使用nspropertylistserialization，那么这个类别可能不适合你。

替换NSDictionary中的所有NSNull对象

8 个答案:

CPJSONDictionary.h

CPJSONDictionary.m