iOS 用宏在category里给对象添加属性

iOS 用宏在category里给对象添加属性

奇技yin巧 指过于奇巧而无益的技艺与制品.

转载请注明出处http://blog.csdn.net/uxyheaven/article/details/46789065
系列文章请看http://blog.csdn.net/uxyheaven/article/category/5800569

众所周知,一般的情况下我们是没办法在category里加属性的.
如果想加,需要用到Associated.

@interface NSObject (XYFlyweightTransmit)
@property (nonatomic, strong) id uxy_flyweightData;
@end

@implementation NSObject (UXYFlyweightTransmit)
- (id)uxy_flyweightData
{
    return objc_getAssociatedObject(self, NSObject_key_flyweightData);
}

- (void)setUxy_flyweightData:(id)flyweightData
{
    objc_setAssociatedObject(self, NSObject_key_flyweightData, flyweightData, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
@end;

如果每次需要写这么多代码才可以实现, 确实很繁琐.
这事可以按照下面的代码封装一下

@interface NSObject (XY_associated)
- (id)uxy_getAssociatedObjectForKey:(const char *)key;
- (id)uxy_retainAssociatedObject:(id)obj forKey:(const char *)key;
- @end

@implementation NSObject (XY_associated)
- (id)uxy_getAssociatedObjectForKey:(const char *)key
{
    const char * propName = key;
    id currValue = objc_getAssociatedObject( self, propName );
    return currValue;
}
- (id)uxy_retainAssociatedObject:(id)obj forKey:(const char *)key;
{
    const char * propName = key;
    id oldValue = objc_getAssociatedObject( self, propName );
    objc_setAssociatedObject( self, propName, obj, OBJC_ASSOCIATION_RETAIN_NONATOMIC );
    return oldValue;
}

这样,我们只需要按照如下方式添加一个属性

- (UIView *)overlay
{
    return [self uxy_getAssociatedObjectForKey:"xy.navigationBar.overlay"];
}

- (void)setOverlay:(UIView *)overlay
{
    [self uxy_retainAssociatedObject:overlay forKey:"xy.navigationBar.overlay"];
}

上面的代码看起来还是有不少重复的地方.可以尝试用一个宏来封装一下.
但是当我们真正写宏的时候发现get方法好写, set方法无从下手.因为后面是跟的一个大写的字母.

不漂亮的解决方法:
* 约定属性用大写字母开头
* 约定下划线开头
* 写宏的时候吧setName名字传进去

不过,本文的标题既然叫奇技yin巧,用的的当然不是上述的方法.
先来看下代码表现起来是怎样的

@interface UINavigationBar (XY)
uxy_property_strong(id, test2);
@end

@implementation UINavigationBar (XY)
uxy_def_property_strong(id, test2)
@end

{
    self.test2 = @"a";
    id c = self.test2;
    NSLog(@"%@", c);
}

实现思路:
在申明属性的时候用setter来修改属性的set方法,在前面加 __ 避开大小写.

具体实现代码如下:

#define uxy_property_strong( __type, __name) \
        @property (nonatomic, strong, setter=set__##__name:, getter=__##__name) __type __name;

#define uxy_def_property_strong( __type, __name) \
        - (__type)__##__name \
        { return [self uxy_getAssociatedObjectForKey:#__name]; } \
        - (void)set__##__name:(id)__##__name \
        { [self uxy_retainAssociatedObject:__##__name forKey:#__name]; }

我们再用元宏metamacro_concat给宏升级一下,让他支持基本类型, 然后取消property前面的@符号, 就有了加属性宏的最终版本uxy_property_basicDataType( __type, __name)

演示代码:

@interface Associated (test)
@uxy_property_basicDataType(int, age);
@uxy_property_basicDataType(NSTimeInterval, time);
@end

@implementation Associated (test)
uxy_def_property_basicDataType(int, age)
uxy_def_property_basicDataType(NSTimeInterval, time)
@end

// 测试代码
UXY_DESCRIBE( test1 )
{
    Associated *associated = [[Associated alloc] init];
    associated.age = 10;
    associated.time = 100.5f;

    UXY_EXPECTED( associated.age == 10 );
    UXY_EXPECTED( associated.time == 100.5f );
}

具体实现代码如下:

/** * Returns A and B concatenated after full macro expansion. */
#define metamacro_concat(A, B) \
        metamacro_concat_(A, B)
#define metamacro_concat_(A, B) A ## B

#define uxy_property_basicDataType( __type, __name) \
        property (nonatomic, assign, setter=set__##__name:, getter=__##__name) __type __name;

#define uxy_def_property_basicDataType( __type, __name) \
        - (__type)__##__name \
        {   \
            NSNumber *number = [self uxy_getAssociatedObjectForKey:#__name]; \
            return metamacro_concat(metamacro_concat(__uxy_, __type), _value)( number ); \
        }   \
        - (void)set__##__name:(__type)__##__name \
        { \
            id value = @(__##__name);\
            [self uxy_setAssignAssociatedObject:value forKey:#__name]; \
        }

#define __uxy_int_value( __nubmer ) [__nubmer intValue]
#define __uxy_BOOL_value( __nubmer ) [__nubmer boolValue]
#define __uxy_NSTimeInterval_value( __nubmer ) [__nubmer doubleValue]