iOS NSObject类别runtime添加Property

#import <Foundation/Foundation.h>
#import <objc/runtime.h>

/**
 The AssociantionPolicy enum determines the association memory management type.
 */

typedef enum {
    ASSIGN_POLICY = OBJC_ASSOCIATION_ASSIGN,
    RETAIN_NONATOMIC_POLICY = OBJC_ASSOCIATION_RETAIN_NONATOMIC,
    COPY_NONATOMIC_POLICY = OBJC_ASSOCIATION_COPY_NONATOMIC,
    RETAIN_POLICY = OBJC_ASSOCIATION_RETAIN,
    COPY_POLICY = OBJC_ASSOCIATION_COPY
}AssociantionPolicy;

@interface NSObject (addRuntimeProperty)

/**
 Sets the association between any property for a specific key.
 
 @param property - the associated object
 @param key - the key to identify the associated object
 @param policy - the memory management policy
 */
- (void)setProperty:(id)property forKey:(char const * const)key withPolicy:(AssociantionPolicy)policy;


/**
 returns the associated object for a given key.
 
 @param key - the key to identify the associated object
 @return the assiciated object
 */
- (id)getPropertyForKey:(char const * const)key;

/**
 determines if there is a object for a given key.
 
 @param key - the key to identify the associated object
 @return a boolean value indicating if there is a associated object for a given key
 */
- (BOOL)hasPropertyForKey:(char const * const)key;

#import "NSObject+addRuntimeProperty.h"

@implementation NSObject (addRuntimeProperty)

- (void)setProperty:(id)property forKey:(char const * const)key withPolicy:(AssociantionPolicy)policy {
    
    // validate input
    NSAssert(property,@"PROPERTY must not be nil.");
    NSAssert(key,@"KEY must not be nil.");
    NSAssert(policy!=0, @"POLICY must not be null.");
    NSAssert([self isValidPolicy:policy],@"POLICY must be valid.");
    
    // associate object
    objc_setAssociatedObject(self, key, property, policy);
}

- (id)getPropertyForKey:(char const * const)key
{
    // validate input
    NSAssert(key,@"KEY must not be nil.");
    NSAssert(objc_getAssociatedObject(self, key)!=nil,@"there is no object for the given KEY.");
    
    // return object
    return objc_getAssociatedObject(self, key);
}

- (BOOL)hasPropertyForKey:(char const * const)key
{
    // validate input
    NSAssert(key,@"KEY must not be nil.");
    
    // return logical result
    return objc_getAssociatedObject(self, key) ? YES : NO;
}

/**
 checks if a given policy is valid
 
 @param policy - the memory management policy
 @return logical result indicating if policy is valid
 */

- (BOOL)isValidPolicy:(AssociantionPolicy)policy
{
    switch ( policy ) {
        case ASSIGN_POLICY:
        case RETAIN_NONATOMIC_POLICY:
        case COPY_NONATOMIC_POLICY:
        case RETAIN_POLICY:
        case COPY_POLICY:
            return YES;
        default:
            return NO;
    }
}

@end