Effective Objective-C 2.0 编写高质量iOS与OS X代码 理解消息转发机制

+ (BOOL)resolveInstanceMethod:(SEL)selector

id autoDictionaryGetter(id self, SEL _cmd);
void autoDictionarySetter(id self, SEL _cmd, id value);

+ (BOOL)resolveInstanceMethod:(SEL)selector
{
     NSString *selectorString = NSStringFromSelector(selector);
     if (/* selector is from a @dynamic property */)
     {
          if([selectorString hasPrefix:@“set”])
          {
               class_addMethod(self, selector, (IMP)autoDictionarySetter, “v@:@“);
          }else {
               class_addMethod(self, selector, (IMP)autoDictionaryGetter, “@@:“);
          }
          return YES;
     }
     return [super resolveInstanceMethod:selector];
}

@interface EOCAutoDictionary : NSObject
@property (nonatomic, strong) NSString *string;
@property (nonatomic, strong) NSNumber *number;
@property (nonatomic, strong) NSDate *date;
@property (nonatomic, strong) id opaqueObject;
@property (nonatomic, strong) NSMutableDictionary *backingStore;
@end 

@interface EOCAutoDictionary
@dynamic string, number, date, opaqueObject;

- (id)init {
     if((self = [super init])){
          _backingStore = [NSMutableDictionary new];
     }
     return self;
}

+ (BOOL)resolveInstanceMethod:(SEL)selector
{
     NSString *selectorString = NSStringFromSelector(selector);
     if([selectorString hasPrefix:@“set”])
     {
         class_addMethod(self, selector, (IMP)autoDictionarySetter, “v@:@“);
      }else {
         class_addMethod(self, selector, (IMP)autoDictionaryGetter, “@@:“);
      }
      return YES; 
}
@end

id autoDictionaryGetter (id self, SEL _cmd)
{
     // Get the backing store from the object 
     EOCAutoDictionary *typedSelf = (EOCAutoDictionary*)self;
     NSMutableDictionary *backingStore = typedSelf.backingStore;
     
     // The key is simply the selector name
     NSString *key = NSStringFromSelector(_cmd);
     
     // Return the value
     return [backingStore objectForKey:key];
}

void autoDictionarySetter(id self,SEL _cmd, id value)
{
     // Get the backing store from the object;
     EOCAutoDictionary *typedSelf = (EOCAutoDictionary*)self;
     NSMutableDictionary *backingStore = typedSelf.backingStore;
 
     // for “ :setOpaqueObject:” tobe “opaqueObject”
     NSString *selectorString = NSStringFromSelector(_cmd);
     NSMutableString *key = [selectorString mutableCopy];

     [key deleteCharactersInRange:NSMakeRange(key.length - 1, 1)];

     [key deleteCharactersInRange:NSMakeRange(0, 3)];
     
     NSString 8lowercaseFistChar = [[key substringToIndex:1] lowercaseString];
     [key replaceCharactersInRange:NSMakeRange(0,1) withString:lowercaseFirstChar];

     if（value)
          [backingStore setObject:value forKey:key];
     else
          [backingStore removeObjectForKey:key];
}