iOS分类添加属性

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我们可以通过runtime来给iOS的分类添加属性.

想添加属性,记住几个关键词,1.@dynamic 2.Associated

1. 首先我们像普通的类一样在.h里头使用@property声明一个属性

    ///xxx+CH.h.这里是xxx类的CH分类的.h文件
    @interface xxx (CH)

    @property (nonatomic ,strong) NSString *name;

    @end

这时,.m中就会出现两个警告

    Property 'name' requires method 'name' to be defined - use @dynamic or provide a method implementation in this category
    Property 'name' requires method 'setName:' to be defined - use @dynamic or provide a method implementation in this category

这时.我们在.m中使用@dynamic修饰一下这个属性名字就没有警告了.

    //xxx+CH.m
    @implementation xxx (CH)

    @dynamic name;

    @end

2.使用runtime的方法动态绑定属性.(“重写”get-set方法)

    ///1.
    //xxx+CH.m
    #import <objc/runtime.h>///记得别忘记导入objc/runtime.h

    @implementation xxx (CH)

    @dynamic name;

    /// name的key
    static char *nameKey = "nameKey";

    - (void)setName:(NSString *)name {
        objc_setAssociatedObject(self, nameKey, name, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    }

    - (NSString *)name {
        id name = objc_getAssociatedObject(self, nameKey);
        if (name) {
            return name;
        } else {
            return @"";
        }
    }

    @end

到此为止,我们就给分类添加好属性了.

注意点:
1.对象有哪些类型

    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. */
};

2.非对象类型的取值.我们可以使用id的getValue来去取值去返回.

    例: 这里我们取一个CGRect值
    - (CGRect)rect {
        id rectResult = objc_getAssociatedObject(self, rectKey);
        if (rect) {
            CGRect rect;
            [rectResult getValue:&rect];
            return rect;
        } else {
            return CGRectZero;
        }
    }