用户定义的运行时属性和关联的对象

Question

I'm currently trying to use User Defined Runtime Attributes in Xcode 6 with the following algorithm:

1. Add custom properties to UIView class using Associated Objects

    #define ASSOCIATED_OBJECT_GETTER_AND_SETTER(propertyType, propertyName, propertyNameWithCapital, associationType) \\ -(void)set##propertyNameWithCapital:(propertyType)_value \\ { \\ objc_setAssociatedObject(self, @selector(propertyName), _value, associationType); \\ } \\ -(propertyType)propertyName \\ { \\ return objc_getAssociatedObject(self, @selector(propertyName)); \\ } \\ @interface eMyTags : NSObject @property (nonatomic) NSString* name; @end @implementation eMyTags @synthesize name; @end @interface UIView (MyTags) @property (nonatomic) eMyTags* myTags; @property (nonatomic) NSString* myName; @end @implementation UIView (MyTags) @dynamic myTags, myName; ASSOCIATED_OBJECT_GETTER_AND_SETTER(eMyTags*, myTags, MyTags, OBJC_ASSOCIATION_RETAIN_NONATOMIC); ASSOCIATED_OBJECT_GETTER_AND_SETTER(NSString*, myName, MyName, OBJC_ASSOCIATION_RETAIN_NONATOMIC); @end 

2. Set values of these properties through Xcode storyboard

3. Access these properties in code during runtime

    -(void)viewDidLoad { [super viewDidLoad]; NSLog(@"myName: %@", view.myName); NSLog(@"myTags.name: %@", view.myTags.name); } 

When i compile and run the output is:

myName: bla
myTags.name: (null)

So why myTags.name is not set? What did i miss? Can't i set User Defined Runtime Attributes of custom types?

Answer 1

Well myTags is not allocated in the memory and nor initialised. On the other hand, the value @"bla" is a string literal which is actually an instance of an NSString and points to a location in memory.