如何从 NSDictionary 中删除空值

Question

I have a JSON Feed:

{
    "count1" = 2;
    "count2" = 2;
    idval = 40;
    level = "<null>";
    "logo_url" = "/assets/logos/default_logo_medium.png";
    name = "Golf Club";
    "role_in_club" = Admin;
}

The problem is the "<null>" . I cannot figure out how to remove it from the NSDictionary before saving it to NSUserDefaults.

Answer 1

Another variation, without (explicit) loop:

NSMutableDictionary *dict = [yourDictionary mutableCopy];
NSArray *keysForNullValues = [dict allKeysForObject:[NSNull null]];
[dict removeObjectsForKeys:keysForNullValues];

Answer 2

Iterate through the dictionary and look for any null entries and remove them.

NSMutableDictionary *prunedDictionary = [NSMutableDictionary dictionary];
for (NSString * key in [yourDictionary allKeys])
{
    if (![[yourDictionary objectForKey:key] isKindOfClass:[NSNull class]])
        [prunedDictionary setObject:[yourDictionary objectForKey:key] forKey:key];
}

After that, prunedDictionary should have all non-null items in the original dictionary.

Answer 3

Use this for remove null from dictionary

- (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;
}

Answer 4

Here is my category-based recursive solution for dictionaries containing dictionaries and arrays which values can also be dictionaries and arrays:

File 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

File 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];
}

Answer 5

To remove it, convert it into a mutable dictionary and remove the object for key "level";

NSDictionary* dict = ....;  // this is the dictionary to modify
NSMutableDictionary* mutableDict = [dict mutableCopy];
[mutableDict removeObjectForKey:@"level"];
dict = [mutableDict copy];

If you don't use ARC, you'll need to add some calls to 'release'.

Update:

If you don't know the name of the key(s) with the "<null>" objects, then you have to iterate:

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];

To locate the "<null>" values, I'm using a string comparison since "<null>" is a string in your sample. But I'm not sure if this is really the case.

Answer 6

I belive this is the most resource saving way

// category implementation on NSDictionary

- (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;
}

Answer 7

I have created a category for NSJSOn serialisation class.

Create a category and import class to use its methods...

// 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;

Answer 8

I tried the solution for your question and i got it

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);

Finally the answer is

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";
}

Answer 9

I am doing in this way.

NSMutableDictionary *prunedDict = [NSMutableDictionary dictionary];
[self enumerateKeysAndObjectsUsingBlock:^(NSString *key, id obj, BOOL *stop) {
  if (![obj isKindOfClass:[NSNull class]]) {
    prunedDict[key] = obj;
  }
}];

Answer 10

the following code is ok when the result is in array or dictionary , you can change the result returned to nil or empty string by editing the code

the function is recursive , so can parse array in dictionary .

-(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;
}

resulting in:

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;
    }
)

Answer 11

Swift 3.0/4.0 Solution

Following is the solution, when JSON have sub-dictionaries . This will go-through all the dictionaries , sub -dictionaries of JSON and remove NULL(NSNull) key-value pair from the JSON .

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>
    }
 }

Answer 12

Add this 3 methods in your view controller, and call this method like this way

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;
}

Answer 13

Modify @sinh99 answer. Use a new NSMutableDictionary to collection no-null values and sub-dictionary values.

- (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;
}

Answer 14

Swift - Nested NSNull supported

First of all, we use Dictionary in Swift instead of NSDictionary .

To remove any NSNull appearance in any nested level (including arrays and dictionaries ), try this:

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
    }
}

_{Note that the key of the dictionary should be String}