如何从 NSDictionary 中删除空值
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【中文标题】如何从 NSDictionary 中删除空值【英文标题】：How to remove a null value from NSDictionary 【发布时间】：2012-12-18 08:44:34 【问题描述】：我有一个 JSON 提要：
"count1" = 2;
"count2" = 2;
idval = 40;
level = "<null>";
"logo_url" = "/assets/logos/default_logo_medium.png";
name = "Golf Club";
"role_in_club" = Admin;
问题是"<null>"。在将其保存到 NSUserDefaults 之前，我无法弄清楚如何将其从 NSDictionary 中删除。
【问题讨论】：
因为您可以将空值保存到 NSUserDefaults。 啊，“在将它们保存到 NSUserDefaults 之前” - 抱歉，还没有阅读。 ***.com/a/40343081/2273338 【参考方案1】：遍历字典并查找任何空条目并将其删除。
NSMutableDictionary *prunedDictionary = [NSMutableDictionary dictionary];
for (NSString * key in [yourDictionary allKeys])
if (![[yourDictionary objectForKey:key] isKindOfClass:[NSNull class]])
[prunedDictionary setObject:[yourDictionary objectForKey:key] forKey:key];
之后，prunedDictionary 应该在原始字典中包含所有非空项。
【讨论】：
我想知道哪个性能更好：创建字典的可变副本，然后从中删除对象或手动将所有值添加到字典中...... @RichardJ.RossIII 除非数组 非常 大，否则真的没关系。如果数组 足够大，我会尝试两种方式，看看哪个最快。【参考方案2】：要删除它，请将其转换为可变字典并删除键“级别”的对象；
NSDictionary* dict = ....; // this is the dictionary to modify
NSMutableDictionary* mutableDict = [dict mutableCopy];
[mutableDict removeObjectForKey:@"level"];
dict = [mutableDict copy];
如果您不使用 ARC，则需要添加一些对“释放”的调用。
更新：
如果您不知道 "<null>" 对象的键名，那么您必须进行迭代：
NSDictionary* dict = ....; // this is the dictionary to modify
NSMutableDictionary* mutableDict = [dict mutableCopy];
for (id key in dict)
id value = [dict objectForKey: key];
if ([@"<null>" isEqual: value])
[mutableDict removeObjectForKey:key];
dict = [mutableDict copy];
为了定位"<null>" 值，我使用了字符串比较，因为"<null>" 是您示例中的字符串。但我不确定是否真的如此。
【讨论】：
事实并非如此。如果它是一个不会有问题的字符串。这里的问题是解析将产生一个NSNull 实例读取“NSUserDefaults 中。<null> 而不是 "<null>"。所以要么值是字符串，要么样本错误。
加布里埃拉你是对的。问题是它正在获取一个存储为“另一种变体，没有（显式）循环：
NSMutableDictionary *dict = [yourDictionary mutableCopy];
NSArray *keysForNullValues = [dict allKeysForObject:[NSNull null]];
[dict removeObjectsForKeys:keysForNullValues];
【讨论】：
同样，您可以通过将 [NSNull null] 替换为 @"" 来删除所有空条目 这是一个很酷的代码，但是如果我们将字典放入数组中，我们可以做什么。【参考方案4】：使用它从字典中删除 null
- (NSMutableDictionary *)recursive:(NSMutableDictionary *)dictionary
for (NSString *key in [dictionary allKeys])
id nullString = [dictionary objectForKey:key];
if ([nullString isKindOfClass:[NSDictionary class]])
[self recursive:(NSMutableDictionary*)nullString];
else
if ((NSString*)nullString == (id)[NSNull null])
[dictionary setValue:@"" forKey:key];
return dictionary;
【讨论】：
用@"" 替换空值，这可能是也可能不是你想要的:-) “[字典 setValue:@"" forKey:key];”这可能会崩溃。子/递归字典可能不是 mutableDictionary。所以我们可以使用一个新的 mutableDictionary 来收集每个非空值和子字典值。【参考方案5】：我相信这是最节省资源的方式
// NSDictionary 上的类别实现
- (NSDictionary *)dictionaryByRemovingNullValues
NSMutableDictionary * d;
for (NSString * key in self)
if (self[key] == [NSNull null])
if (d == nil)
d = [NSMutableDictionary dictionaryWithDictionary:self];
[d removeObjectForKey:key];
if (d == nil)
return self;
return d;
【讨论】：
【参考方案6】：我已经为 NSJSOn 序列化类创建了一个类别。
创建一个类别并导入类以使用其方法...
// Mutable containers are required to remove nulls.
if (replacingNulls)
// Force add NSJSONReadingMutableContainers since the null removal depends on it.
opt = opt || NSJSONReadingMutableContainers;
id JSONObject = [self JSONObjectWithData:data options:opt error:error];
if ((error && *error) || !replacingNulls)
return JSONObject;
[JSONObject recursivelyReplaceNullsIgnoringArrays:ignoreArrays withString:replaceString];
return JSONObject;
【讨论】：
【参考方案7】：这是我的基于类别的递归解决方案，用于包含字典和数组的字典，其中值也可以是字典和数组：
文件NSDictionary+Dario.m：
#import "NSArray+Dario.h"
@implementation NSDictionary (Dario)
- (NSDictionary *) dictionaryByReplacingNullsWithEmptyStrings
const NSMutableDictionary *replaced = [NSMutableDictionary new];
const id nul = [NSNull null];
const NSString *blank = @"";
for(NSString *key in self)
const id object = [self objectForKey:key];
if(object == nul)
[replaced setObject:blank forKey:key];
else if ([object isKindOfClass:[NSDictionary class]])
[replaced setObject:[object dictionaryByReplacingNullsWithEmptyStrings] forKey:key];
else if ([object isKindOfClass:[NSArray class]])
[replaced setObject:[object arrayByReplacingNullsWithEmptyStrings] forKey:key];
else
[replaced setObject:object forKey:key];
return [NSDictionary dictionaryWithDictionary:(NSDictionary*)replaced];
@end
文件NSArray+Dario.m：
#import "NSDictionary+Dario.h"
@implementation NSArray (Dario)
- (NSArray *) arrayByReplacingNullsWithEmptyStrings
const NSMutableArray *replaced = [NSMutableArray new];
const id nul = [NSNull null];
const NSString *blank = @"";
for (int i=0; i<[self count]; i++)
const id object = [self objectAtIndex:i];
if ([object isKindOfClass:[NSDictionary class]])
[replaced setObject:[object dictionaryByReplacingNullsWithEmptyStrings] atIndexedSubscript:i];
else if ([object isKindOfClass:[NSArray class]])
[replaced setObject:[object arrayByReplacingNullsWithEmptyStrings] atIndexedSubscript:i];
else if (object == nul)
[replaced setObject:blank atIndexedSubscript:i];
else
[replaced setObject:object atIndexedSubscript:i];
return [NSArray arrayWithArray:(NSArray*)replaced];
【讨论】：
【参考方案8】：我尝试了你的问题的解决方案，我明白了
NSDictionary *dict = [[NSDictionary alloc]initWithObjectsAndKeys:@"2",@"count1",@"2",@"count2",@"40",@"idval",@"<null>",@"level",@"/assets/logos/default_logo_medium.png",@"logo_url",@"Golf Club",@"name",@"role_in_club",@"Admin", nil];
NSMutableDictionary *mutableDict = [dict mutableCopy];
for (NSString *key in [dict allKeys])
if ([dict[key] isEqual:[NSNull null]])
mutableDict[key] = @"";
if([dict[key] isEqualToString:@"<null>"])
mutableDict[key] = @"";
dict = [mutableDict copy];
NSLog(@"The dict is - %@",dict);
最终答案是
The dict is -
Admin = "role_in_club";
count1 = 2;
count2 = 2;
idval = 40;
level = "";
"logo_url" = "/assets/logos/default_logo_medium.png";
name = "Golf Club";
【讨论】：
我试过了，然后我才用结果发布了我的答案。它有效。【参考方案9】：我就是这样做的。
NSMutableDictionary *prunedDict = [NSMutableDictionary dictionary];
[self enumerateKeysAndObjectsUsingBlock:^(NSString *key, id obj, BOOL *stop)
if (![obj isKindOfClass:[NSNull class]])
prunedDict[key] = obj;
];
【讨论】：
【参考方案10】：以下代码在结果为数组或字典的情况下是可以的，你可以通过编辑代码将返回的结果更改为nil或空字符串
函数是递归的，所以可以解析字典中的数组。
-(id)changeNull:(id)sender
id newObj;
if ([sender isKindOfClass:[NSArray class]])
NSMutableArray *newArray = [[NSMutableArray alloc] init];
for (id item in sender)
[newArray addObject:[self changeNull:item]];
newObj = newArray;
else if ([sender isKindOfClass:[NSDictionary class]])
NSMutableDictionary *newDict = [[NSMutableDictionary alloc] init];
for (NSString *key in sender)
NSDictionary *oldDict = (NSDictionary*)sender;
id item = oldDict[key];
if (![item isKindOfClass:[NSDictionary class]] && ![item isKindOfClass:[NSArray class]])
if ([item isEqual:[NSNull null]])
item = @"";
[newDict setValue:item forKey:key];
else
[newDict setValue:[self changeNull:item] forKey:key];
newObj = newDict;
return newObj;
导致：
jsonresult (
Description = "<null>";
Id = 1;
Name = High;
,
Description = "<null>";
Id = 2;
Name = Medium;
,
Description = "<null>";
Id = 3;
Name = Low;
)
change null (
Description = "";
Id = 1;
Name = High;
,
Description = "";
Id = 2;
Name = Medium;
,
Description = "";
Id = 3;
Name = Low;
)
【讨论】：
【参考方案11】：Swift 3.0/4.0解决方案
以下是解决方案，当JSON 拥有sub-dictionaries。这将遍历所有dictionaries、JSON 的子-dictionaries 并从JSON 中删除NULL(NSNull) key-value 对。
extension Dictionary
func removeNull() -> Dictionary
let mainDict = NSMutableDictionary.init(dictionary: self)
for _dict in mainDict
if _dict.value is NSNull
mainDict.removeObject(forKey: _dict.key)
if _dict.value is NSDictionary
let test1 = (_dict.value as! NSDictionary).filter( $0.value is NSNull ).map( $0 )
let mutableDict = NSMutableDictionary.init(dictionary: _dict.value as! NSDictionary)
for test in test1
mutableDict.removeObject(forKey: test.key)
mainDict.removeObject(forKey: _dict.key)
mainDict.setValue(mutableDict, forKey: _dict.key as? String ?? "")
if _dict.value is NSArray
let mutableArray = NSMutableArray.init(object: _dict.value)
for (index,element) in mutableArray.enumerated() where element is NSDictionary
let test1 = (element as! NSDictionary).filter( $0.value is NSNull ).map( $0 )
let mutableDict = NSMutableDictionary.init(dictionary: element as! NSDictionary)
for test in test1
mutableDict.removeObject(forKey: test.key)
mutableArray.replaceObject(at: index, with: mutableDict)
mainDict.removeObject(forKey: _dict.key)
mainDict.setValue(mutableArray, forKey: _dict.key as? String ?? "")
return mainDict as! Dictionary<Key, Value>
【讨论】：
谢谢，我已经更新了我的答案。实际上嵌入链接的答案也是我发布的。【参考方案12】：在你的视图控制器中添加这3个方法，并像这样调用这个方法
NSDictionary *dictSLoginData = [self removeNull:[result valueForKey:@"data"]];
- (NSDictionary*)removeNull:(NSDictionary *)dict
NSMutableDictionary *replaced = [NSMutableDictionary dictionaryWithDictionary: dict];
const id nul = [NSNull null];
const NSString *blank = @"";
for (NSString *key in [dict allKeys])
const id object = [dict objectForKey: key];
if (object == nul)
[replaced setObject: blank forKey: key];
else if([object isKindOfClass: [NSDictionary class]])
[replaced setObject: [self replaceNull:object] forKey: key];
else if([object isKindOfClass: [NSArray class]])
[replaced setObject: [self replaceNullArray:object] forKey: key];
return [NSDictionary dictionaryWithDictionary: replaced];
- (NSArray *)replaceNullArray:(NSArray *)array
const id nul = [NSNull null];
const NSString *blank = @"";
NSMutableArray *replaced = [NSMutableArray arrayWithArray:array];
for (int i=0; i < [array count]; i++)
const id object = [array objectAtIndex:i];
if (object == nul)
[replaced replaceObjectAtIndex:i withObject:blank];
else if([object isKindOfClass: [NSDictionary class]])
[replaced replaceObjectAtIndex:i withObject:[self replaceNull:object]];
else if([object isKindOfClass: [NSArray class]])
[replaced replaceObjectAtIndex:i withObject:[self replaceNullArray:object]];
return replaced;
- (NSDictionary *)replaceNull:(NSDictionary *)dict
const id nul = [NSNull null];
const NSString *blank = @"";
NSMutableDictionary *replaced = [NSMutableDictionary dictionaryWithDictionary: dict];
for (NSString *key in [dict allKeys])
const id object = [dict objectForKey: key];
if (object == nul)
[replaced setObject: blank forKey: key];
else if ([object isKindOfClass: [NSDictionary class]])
[replaced setObject: [self replaceNull:object] forKey: key];
else if([object isKindOfClass: [NSArray class]])
[replaced setObject: [self replaceNullArray:object] forKey: key];
return replaced;
【讨论】：
【参考方案13】：修改@sinh99 答案。使用新的 NSMutableDictionary 来收集非空值和子字典值。
- (NSMutableDictionary *)recursiveRemoveNullValues:(NSDictionary *)dictionary
NSMutableDictionary *mDictionary = [NSMutableDictionary new];
for (NSString *key in [dictionary allKeys])
id nullString = [dictionary objectForKey:key];
if ([nullString isKindOfClass:[NSDictionary class]])
NSMutableDictionary *mDictionary_sub = [self recursiveRemoveNullValues:(NSDictionary*)nullString];
[mDictionary setObject:mDictionary_sub forKey:key];
else
if ((NSString*)nullString == (id)[NSNull null])
[mDictionary setValue:@"" forKey:key];
else
[mDictionary setValue:nullString forKey:key];
return mDictionary;
【讨论】：
【参考方案14】：Swift - 支持嵌套 NSNull
首先，我们在 Swift 中使用Dictionary 而不是NSDictionary。
要删除任何嵌套级别（包括数组和字典）中的任何 NSNull外观，请尝试以下操作：
extension Dictionary where Key == String
func removeNullsFromDictionary() -> Self
var destination = Self()
for key in self.keys
guard !(self[key] is NSNull) else destination[key] = nil; continue
guard !(self[key] is Self) else destination[key] = (self[key] as! Self).removeNullsFromDictionary() as? Value; continue
guard self[key] is [Value] else destination[key] = self[key]; continue
let orgArray = self[key] as! [Value]
var destArray: [Value] = []
for item in orgArray
guard let this = item as? Self else destArray.append(item); continue
destArray.append(this.removeNullsFromDictionary() as! Value)
destination[key] = destArray as? Value
return destination
注意字典的key应该是String
【讨论】：
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