利用类别(Category)为对象添加”实例变量”

主要利用ObjectiveC的C API中函数:

void objc_setAssociatedObject(id object, const void *key, id value, objc_AssociationPolicy policy)

id objc_getAssociatedObject(id object, const void *key)

原理详细参见官方的ObjectiveC Runtime Reference.

好了,现在直接写怎么做了.

1.在定义类别之前, 引入runtime.

#import <objc/runtime.h>

2.定义&实现类别(以UIView为例)

定义:

@interface UIView(AddVariables)

 

@property (nonatomic, retain) NSString *viewName;

 

@end

实现:

// 定义存取的Key

static const char *viewNameKey = "viewNameKey";

 

@implementation UIView(AddVariables)

 

// get方法

- (NSString *)viewName {

    return (NSString *)objc_getAssociatedObject(self, viewNameKey);

}

// set方法

- (void)setViewName:(NSString *)newViewNameKey {

    objc_setAssociatedObject(self, viewNameKey, newViewNameKey, OBJC_ASSOCIATION_RETAIN_NONATOMIC);

}

 

@end

3.调用测试:

- (void)viewDidLoad {

 

    UIView *testView = [[UIView alloc] initWithFrame:self.view.bounds];

    [self.view addSubview:testView];

    [testView release];

 

    [testView setViewName:@"Nori's View"];

    NSLog(@"[testView's newPropery]:%@", testView.viewName);

 

    [super viewDidLoad];

}

输出结果如下:

testView's newPropery:Nori's View