Question

我觉得这是一个愚蠢的问题，但无论如何我都会问......

我有一组NSDictionary个对象，其键/值对对应于我创建的自定义类，称之为MyClass。我是否有一种简单或“最佳实践”的方法，基本上可以将MyClass * instance = [地图NSDictionary属性添加到MyClass ];？我有一种感觉，我需要对NSCoding或NSKeyedUnarchiver做些什么，而不是自己偶然发现它，我觉得有人可能会指出我正确的方向。

Answer 1

-setValuesForKeysWithDictionary：方法和-dictionaryWithValuesForKeys：是你想要使用的。

示例：

// In your custom class
+ (id)customClassWithProperties:(NSDictionary *)properties {
   return [[[self alloc] initWithProperties:properties] autorelease];
}

- (id)initWithProperties:(NSDictionary *)properties {
   if (self = [self init]) {
      [self setValuesForKeysWithDictionary:properties];
   }
   return self;
}

// ...and to easily derive the dictionary
NSDictionary *properties = [anObject dictionaryWithValuesForKeys:[anObject allKeys]];

Answer 2

NSObject上没有allKeys。你需要在NSObject上创建一个额外的类别，如下所示：

NSObject的+ PropertyArray.h

@interface NSObject (PropertyArray)
- (NSArray *) allKeys;
@end

NSObject的+ PropertyArray.m

#import <objc/runtime.h>

@implementation NSObject (PropertyArray)
- (NSArray *) allKeys {
    Class clazz = [self class];
    u_int count;

    objc_property_t* properties = class_copyPropertyList(clazz, &count);
    NSMutableArray* propertyArray = [NSMutableArray arrayWithCapacity:count];
    for (int i = 0; i < count ; i++) {
        const char* propertyName = property_getName(properties[i]);
        [propertyArray addObject:[NSString  stringWithCString:propertyName encoding:NSUTF8StringEncoding]];
    }
    free(properties);

   return [NSArray arrayWithArray:propertyArray];
}
@end

示例：

#import "NSObject+PropertyArray.h"

...

MyObject *obj = [[MyObject alloc] init];
obj.a = @"Hello A";  //setting some values to attributes
obj.b = @"Hello B";

//dictionaryWithValuesForKeys requires keys in NSArray. You can now
//construct such NSArray using `allKeys` from NSObject(PropertyArray) category
NSDictionary *objDict = [obj dictionaryWithValuesForKeys:[obj allKeys]];

//Resurrect MyObject from NSDictionary using setValuesForKeysWithDictionary
MyObject *objResur = [[MyObject alloc] init];
[objResur setValuesForKeysWithDictionary:objDict];

Answer 3

假设您的类符合Key-Value Coding协议，您可以使用以下内容:(为方便起见，在NSDictionary上定义为类别）：

// myNSDictionaryCategory.h:
@interface NSDictionary (myCategory)
- (void)mapPropertiesToObject:(id)instance
@end

// myNSDictionaryCategory.m:
- (void)mapPropertiesToObject:(id)instance
{
    for (NSString * propertyKey in [self allKeys])
    {
        [instance setValue:[self objectForKey:propertyKey]
                    forKey:propertyKey];
    }
}

以下是您将如何使用它：

#import "myNSDictionaryCategory.h"
//...
[someDictionary mapPropertiesToObject:someObject];

Answer 4

如果你做这种事情的机会是你处理JSON，你应该看看Mantle https://github.com/Mantle/Mantle

然后，您将获得一个方便的方法dictionaryValue

[anObject dictionaryValue];

Answer 5

只需为NSObject添加类别，以便从自定义对象中获取dictionaryRepresentation（在我的情况下仅使用JSON序列化）：

//  NSObject+JSONSerialize.h
#import <Foundation/Foundation.h>

@interface NSObject(JSONSerialize)

- (NSDictionary *)dictionaryRepresentation;

@end

//  NSObject+JSONSerialize.m
#import "NSObject+JSONSerialize.h"
#import <objc/runtime.h>

@implementation NSObject(JSONSerialize)

+ (instancetype)instanceWithDictionary:(NSDictionary *)aDictionary {
    return [[self alloc] initWithDictionary:aDictionary];
}

- (instancetype)initWithDictionary:(NSDictionary *)aDictionary {
    aDictionary = [aDictionary clean];

    self.isReady = NO;

    for (NSString* propName in [self allPropertyNames]) {
        [self setValue:aDictionary[propName] forKey:propName];
    }

    //You can add there some custom properties with wrong names like "id"
    //[self setValue:aDictionary[@"id"] forKeyPath:@"objectID"];
    self.isReady = YES;

    return self;
}

- (NSDictionary *)dictionaryRepresentation {
    NSMutableDictionary *result = [NSMutableDictionary dictionary];
    NSArray *propertyNames = [self allPropertyNames];

    id object;
    for (NSString *key in propertyNames) {
        object = [self valueForKey:key];
        if (object) {
            [result setObject:object forKey:key];
        }
    }

    return result;
}

- (NSArray *)allPropertyNames {
    unsigned count;
    objc_property_t *properties = class_copyPropertyList([self class], &count);

    NSMutableArray *rv = [NSMutableArray array];

    unsigned i;
    for (i = 0; i < count; i++) {
        objc_property_t property = properties[i];
        NSString *name = [NSString stringWithUTF8String:property_getName(property)];
        [rv addObject:name];
    }
    //You can add there some custom properties with wrong names like "id"
    //[rv addObject:@"objectID"];
    //Example use inside initWithDictionary:
    //[self setValue:aDictionary[@"id"] forKeyPath:@"objectID"];

    free(properties);

    return rv;
}

@end

此外，您可以看到我的解决方案不适用于具有嵌套对象或数组的自定义对象。对于数组 - 只需更改dictionaryRepresentation方法中的代码行：

    if (object) {
        if ([object isKindOfClass:[NSArray class]]) {
            @autoreleasepool {
                NSMutableArray *array = [NSMutableArray array];
                for (id item in (NSArray *)object) {
                    [array addObject:[item dictionaryRepresentation]];
                }

                [result setObject:array forKey:key];
            }
        } else {
            [result setObject:object forKey:key];
        }
    }

从NSDictionary实例化自定义类

5 个答案: