iOS: 把对象直接转化成NSDictionary或JSON

1. 使用

实现的结果就是可以把任何对象转化成字典或者字典对应的JSON。字典的数据就是来自对象的属性名称和属性值 。而且是多层的，也就是说如果对象的某个属性值是另一个对象，数组，或者字典，该值都会被转换成另一个字典。

这个类型名称是PrintObject，它的所有方法都是静态的：

@interface PrintObject : NSObject
//通过对象返回一个NSDictionary，键是属性名称，值是属性值。
+ (NSDictionary*)getObjectData:(id)obj;

//将getObjectData方法返回的NSDictionary转化成JSON
+ (NSData*)getJSON:(id)obj options:(NSJSONWritingOptions)options error:(NSError**)error;

//直接通过NSLog输出getObjectData方法返回的NSDictionary
+ (void)print:(id)obj;

@end

举个例子，比如用来保存数据的类型是MyData， 这个类型如下定义：

@interface MyData : NSObject
@property (nonatomic, strong) NSString *name;
@property (nonatomic, strong) NSString *nullString;
@property (nonatomic) int age;
@property (nonatomic) BOOL male;
@property (nonatomic, strong) MyData *objProp;
@property (nonatomic, strong) NSArray *arrProp;
@property (nonatomic, strong) NSDictionary *dicProp;
@end

然后通过MyData类型创建一个复杂的对象，其中包含非对象属性，对象属性，还有包含对象的数组和字典。代码如下：

MyData *main = [[MyData alloc] init];
main.name = @"mgen";
main.age = 22;
MyData *childOfChild = [[MyData alloc] init];
childOfChild.name = @"child of child";
childOfChild.age = -443;
MyData *child = [[MyData alloc] init];
child.name = @"child";
child.arrProp = @[@"test", @234, @[@123, @"array in array", childOfChild]];
main.objProp = child;
main.dicProp = @{@"中文Key": @3.444444, @"object": childOfChild};

OK，接着使用PrintObject类型输出这个MyData对象（上面的main变量）的字典：

NSDictionary *dic = [PrintObject getObjectData:main];
NSLog(@"%@", dic);

输出：

{
    age = 22;
    arrProp = "<null>";
    dicProp =     {
        object =         {
            age = "-443";
            arrProp = "<null>";
            dicProp = "<null>";
            male = 0;
            name = "child of child";
            nullString = "<null>";
            objProp = "<null>";
        };
        "\U4e2d\U6587Key"= "3.444444";
    };
    male = 0;
    name = mgen;
    nullString = "<null>";
    objProp =     {
        age = 0;
        arrProp =         (
            test,
            234,
                        (
                123,
                "array in array",
                                {
                    age = "-443";
                    arrProp = "<null>";
                    dicProp = "<null>";
                    male = 0;
                    name = "child of child";
                    nullString = "<null>";
                    objProp = "<null>";
                }
            )
        );
        dicProp = "<null>";
        male = 0;
        name = child;
        nullString = "<null>";
        objProp = "<null>";
    };
}

也可以输出这个对象的JSON数据

NSData *jsonData = [PrintObject getJSON:main options:NSJSONWritingPrettyPrinted error:nil];
NSString *jsonText = [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];
NSLog(@"%@", jsonText);

结果：

{
  "arrProp": null,
  "name": "mgen",
  "age": 22,
  "objProp": {
    "arrProp": [
      "test",
      234,
      [
        123,
        "array in array",
        {
          "arrProp": null,
          "name": "child of child",
          "age": -443,
          "objProp": null,
          "male": 0,
          "nullString": null,
          "dicProp": null
        }
      ]
    ],
    "name": "child",
    "age": 0,
    "objProp": null,
    "male": 0,
    "nullString": null,
    "dicProp": null
  },
  "male": 0,
  "nullString": null,
  "dicProp": {
    "中文Key": 3.444444,
    "object": {
      "arrProp": null,
      "name": "child of child",
      "age": -443,
      "objProp": null,
      "male": 0,
      "nullString": null,
      "dicProp": null
    }
  }
}

2. 实现

在实现上，属性的枚举是通过定义在<objc/runtime.h>中的class_copyPropertyList方法实现。其次，属性值的获取是通过KVC中的valueForKey方法，这个方法同时可以将非对象类型（如BOOL, int等）转换成NSNumber。

接着就是对数组，字典和对象类型值的嵌套处理，所有值就可以获取出来了。

至于JSON，如果正确获取了NSDictionary后，直接使用iOS 5后的NSJSONSerialization类型的dataWithJSONObject方法就可以返回包含JSON字符串的NSData对象了。

3. 下载和代码

源代码下载 下载页面 

注意：链接是微软SkyDrive页面，下载时请用浏览器直接下载，用某些下载工具可能无法下载 

源代码环境：Xcode 4.6.3

PrintObject.h

#import <Foundation/Foundation.h>

@interface PrintObject : NSObject
//通过对象返回一个NSDictionary，键是属性名称，值是属性值。
+ (NSDictionary*)getObjectData:(id)obj;

//将getObjectData方法返回的NSDictionary转化成JSON
+ (NSData*)getJSON:(id)obj options:(NSJSONWritingOptions)options error:(NSError**)error;

//直接通过NSLog输出getObjectData方法返回的NSDictionary
+ (void)print:(id)obj;

@end

PrintObject.m

#import "PrintObject.h"
#import <objc/runtime.h>

@implementation PrintObject

+ (NSDictionary*)getObjectData:(id)obj
{
    NSMutableDictionary *dic = [NSMutableDictionary dictionary];
    unsigned int propsCount;
    objc_property_t *props = class_copyPropertyList([obj class], &propsCount);
    for(int i = 0;i < propsCount; i++)
    {
        objc_property_t prop = props[i];

        NSString *propName = [NSString stringWithUTF8String:property_getName(prop)];
        id value = [obj valueForKey:propName];
        if(value == nil)
        {
            value = [NSNull null];
        }
        else
        {
            value = [self getObjectInternal:value];
        }
        [dic setObject:value forKey:propName];
    }
    returndic;
}

+ (void)print:(id)obj
{
    NSLog(@"%@", [self getObjectData:obj]);
}


+ (NSData*)getJSON:(id)obj options:(NSJSONWritingOptions)options error:(NSError**)error
{
    return[NSJSONSerialization dataWithJSONObject:[self getObjectData:obj] options:options error:error];
}

+ (id)getObjectInternal:(id)obj
{
    if([obj isKindOfClass:[NSString class]]
       || [obj isKindOfClass:[NSNumber class]]
       || [obj isKindOfClass:[NSNull class]])
    {
        returnobj;
    }

    if([obj isKindOfClass:[NSArray class]])
    {
        NSArray *objarr = obj;
        NSMutableArray *arr = [NSMutableArray arrayWithCapacity:objarr.count];
        for(int i = 0;i < objarr.count; i++)
        {
            [arr setObject:[self getObjectInternal:[objarr objectAtIndex:i]] atIndexedSubscript:i];
        }
        returnarr;
    }

    if([obj isKindOfClass:[NSDictionary class]])
    {
        NSDictionary *objdic = obj;
        NSMutableDictionary *dic = [NSMutableDictionary dictionaryWithCapacity:[objdic count]];
        for(NSString *key inobjdic.allKeys)
        {
            [dic setObject:[self getObjectInternal:[objdic objectForKey:key]] forKey:key];
        }
        returndic;
    }
    return[self getObjectData:obj];
}

@end