關(guān)聯(lián)對(duì)象(Associated Object)
- category是object-c的分類，通常用來(lái)對(duì)類進(jìn)行擴(kuò)展，添加方法。如果直接添加屬性的話捏膨，并不能使用，因?yàn)橄到y(tǒng)只會(huì)生成一個(gè)聲明食侮，并不像在普通類里面号涯，屬性會(huì)自動(dòng)生成成員變量和set，get方法锯七。如果要在分類里面添加屬性的話链快，關(guān)聯(lián)對(duì)象就派上用場(chǎng)了。
- 關(guān)聯(lián)對(duì)象類似于成員變量眉尸，不過是在運(yùn)行時(shí)添加的域蜗，需要我們手動(dòng)添加set和get方法巨双。在set和get中分別使用void objc_setAssociatedObject(id object, const void *key, id value, objc_AssociationPolicy policy)和void objc_setAssociatedObject(id object, const void *key, id value, objc_AssociationPolicy policy) 方法。
- 我們還需要指定一個(gè)內(nèi)存管理策略霉祸，以告訴Runtime如何管理這個(gè)對(duì)象的內(nèi)存筑累。這個(gè)內(nèi)存管理的策略可以由以下值指定：
<pre>
/**
- Policies related to associative references.
- These are options to objc_setAssociatedObject()
/
typedef OBJC_ENUM(uintptr_t, objc_AssociationPolicy) {
OBJC_ASSOCIATION_ASSIGN = 0, /< Specifies a weak reference to the associated object. /
OBJC_ASSOCIATION_RETAIN_NONATOMIC = 1, /< Specifies a strong reference to the associated object.
* The association is not made atomically. /
OBJC_ASSOCIATION_COPY_NONATOMIC = 3, /< Specifies that the associated object is copied.
* The association is not made atomically. /
OBJC_ASSOCIATION_RETAIN = 01401, /< Specifies a strong reference to the associated object.
* The association is made atomically. /
OBJC_ASSOCIATION_COPY = 01403 /*< Specifies that the associated object is copied.
* The association is made atomically. */
};
</pre>
關(guān)聯(lián)對(duì)象最佳實(shí)踐
關(guān)聯(lián)對(duì)象理解起來(lái)不難，實(shí)際使用也很容易丝蹭，但是不能濫用慢宗，以下是一個(gè)實(shí)際使用的例子。
- People的h文件
<pre>
@interface People : NSObject
{
NSString * _name;
NSString * _reName;
}
@property (nonatomic,assign) NSInteger age;
@property (nonatomic,strong) NSString *country;
/**
- 初始化
- @param reName
- @param reName
- @return
*/
- (instancetype)initWithName:(NSString )name reName:(NSString )reName;
/
- 獲取所有的成員變量
- @return
*/
- (NSDictionary )allIvar;
/*
- 獲取所有的
- @return return value description
*/
- (NSDictionary *)allProperty;
@end
</pre>
- People類的分類奔穿，添加了company和position兩個(gè)關(guān)聯(lián)對(duì)象
<pre>
@interface People (BTExtend)
//在分類里直接添加屬性的話镜沽，并不會(huì)生成成員變量和set以及get方法
@property (nonatomic, copy) NSString *company;
@property (nonatomic, strong) NSString *position;
@end
@implementation People (BTExtend)
(NSString *)company
{
return objc_getAssociatedObject(self, _cmd);
}(void)setCompany:(NSString *)company
{
objc_setAssociatedObject(self, @selector(company), company, OBJC_ASSOCIATION_COPY_NONATOMIC);
}(NSString *)position
{
return objc_getAssociatedObject(self, _cmd);
}(void)setPosition:(NSString *)position
{
objc_setAssociatedObject(self, @selector(position), position, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
@end
</pre>遍歷People實(shí)例對(duì)象的成員變量和屬性
<pre>
void ivarAndPropertyList()
{
People *people = [[People alloc] initWithName:@"大傻" reName:@"二傻"];
people.age = 18;
people.country = @"japan";
people.company = @"tv";
people.position = @"av";
NSDictionary *ivarList = [people allIvar];
NSDictionary *propertyList = [people allProperty];
NSLog(@"ivarList:%@\npropertyList:%@",ivarList,propertyList);
}
//運(yùn)行結(jié)果
2016-06-06 22:22:49.271 runtimeDemo[1368:49233] ivarList:{
** "_age" = 18;**
** "_country" = japan;**
** "_name" = "\U5927\U50bb";**
** "_reName" = "\U4e8c\U50bb";**
}
propertyList:{
** age = 18;**
** company = tv;**
** country = japan;**
** position = av;**
}
</pre>
