从 NSDictionary 实例化自定义类

Question

我觉得这是个愚蠢的问题，但我还是会问...

我有一个NSDictionary 对象的集合，它们的键/值对对应于我创建的自定义类，称之为MyClass。有没有一种简单或“最佳实践”的方法可以让我基本上做类似MyClass * instance = [map NSDictionary 属性到MyClass ]; 的事情？我觉得我需要对 NSCoding 或 NSKeyedUnarchiver 做点什么，但与其自己跌跌撞撞，我想有人可以为我指明正确的方向。

Answer 1

-setValuesForKeysWithDictionary: 方法以及 -dictionaryWithValuesForKeys: 是您想要使用的方法。

例子：

// 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。您需要在 NSObject 上创建一个额外的类别，如下所示：

NSObject+PropertyArray.h

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

NSObject+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

例子：

#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];
    }
}

以下是你将如何使用它：

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

Answer 4

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

你会得到一个方便的方法dictionaryValue

[anObject dictionaryValue];

Answer 5

只需为 NSObject 添加类别，以便从您的自定义对象中获取 dictionaryRepresentation（在我的情况下，仅在 JSON 序列化中使用）：

//  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];
        }
    }