Associated Objects 介绍
<objc/runtime.h> 中的函数号称是iOS中最后一把神兵利刃，具有其他方式做不到的，能为应用和框架提供强大功能的能力。但使用不当也可能废掉代码的,一切代码和逻辑都可能被异常糟糕的副作用影响。
就像和魔鬼做交易一样常常让人怀着巨大的恐惧。
历史
对象关联（或称为关联引用）本来是 Objective-C 2.0 运行时的一个特性，起始于 OS X Snow Leopard 和 iOS4 。
核心函数 3 个 – 允许将任何键值在允许时关联到对象上
- objc_setAssociatedObject
- objc_getAssociatedObject
- objc_removeAssociatedObjects
这有什么用呢？这允许开发者对已经存在的类在扩展中添加自定义的属性
实现的 3 种方式
static char selector _cmd_
使用 static char 实现
NSObject+AssociatedObject.h
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| @interface NSObject (AssociatedObject)
@property (nonatomic, strong) id associatedObject;
@end
|
NSObject+AssociatedObject.m
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| @implementation NSObject (AssociatedObject)
static char kAssociatedObjectKey;
- (id)associatedObject
{
return objc_getAssociatedObject(self,&kAssociatedObjectKey);
}
- (void)setAssociatedObject:(id)associatedObject
{
objc_setAssociatedObject(self, &kAssociatedObjectKey, associatedObject, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
@end
|
使用 selector 实现
NSObject+AssociatedObject.h
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| @interface NSObject (AssociatedObject)
@property (nonatomic, strong) id associatedObject;
@end
|
NSObject+AssociatedObject.m
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| @implementation NSObject (AssociatedObject)
- (id)associatedObject
{
return objc_getAssociatedObject(self, @selector(associatedObject));
}
- (void)setAssociatedObject:(id)associatedObject
{
objc_setAssociatedObject(self, @selector(associatedObject), associatedObject, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
@end
|
使用 _cmd_ 实现
NSObject+AssociatedObject.h
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| @interface NSObject (AssociatedObject)
@property (nonatomic, strong) id associatedObject;
@end
|
NSObject+AssociatedObject.m
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| @implementation NSObject (AssociatedObject)
- (id)associatedObject
{
return objc_getAssociatedObject(self, _cmd_);
}
- (void)setAssociatedObject:(id)associatedObject
{
objc_setAssociatedObject(self, @selector(associatedObject), associatedObject, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
@end
|
关联对象的行为
属性根据枚举类型 objc_AssociationPolicy 来决定被关联在对象上的行为：
| Behavior |
与之等效的@property |
| OBJC_ASSOCIATION_ASSIGN |
@property (assign) 或 @property (unsafe_unretained) |
| OBJC_ASSOCIATION_RETAIN_NONATOMIC |
@property (nonatomic, strong) |
| OBJC_ASSOCIATION_COPY_NONATOMIC |
@property (nonatomic, copy) |
| OBJC_ASSOCIATION_RETAIN |
@property (atomic, strong) |
| OBJC_ASSOCIATION_COPY |
@property (atomic, copy) |
OBJC_ASSOCIATION_ASSIGN 类型关联对象的弱引用不代表weak的弱引用，行为上更像 unsafe_unretained 属性。
对象销毁时间
被关联的对象在声明周期内比对象本身释放要晚很多，在对象调用 -dealloc 中的 object_dispose() 中释放。
删除属性
你或许想要使用 objc_removeAssociatedObjects（） 来进行删除操作，但官方文档不建议手动调用这个函数。
这个函数可能会把其他用户对其添加的属性也移除了，正确的方式是调用 objc_setAssociatedObject 方法，传入 nil 值来清除一个关联属性。
优秀样例
- 添加私有属性用于更好地去实现细节。
- 添加 public 属性来增强 category 的功能。
- 创建一个用于 KVO 的关联观察者。
应用举例
UIImagePickerController 图片选择回调
关联一个 block 实现完成选择图片后的回调。
UIImagePickerController+RFBlocks.h
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| @interface UIImagePickerController (RFBlocks)<UIImagePickerControllerDelegate, UINavigationControllerDelegate>
typedef void(^RFImagePickerFinishBlock)(NSDictionary *info);
@property (nonatomic, copy) RFImagePickerFinishBlock rf_finishBlock;
+ (UIImagePickerController *)rf_imagePickerWithFinishBlock:(RFImagePickerFinishBlock)finishBlock;
@end
|
UIImagePickerController+RFBlocks.m
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| static const char kFinishBlockKey;
@implementation UIImagePickerController (RFBlocks)
+ (UIImagePickerController *)rf_imagePickerWithFinishBlock:(RFImagePickerFinishBlock)finishBlock
{
UIImagePickerController *picker = [[UIImagePickerController alloc] init];
picker.rf_finishBlock = finishBlock;
return picker;
}
- (RFImagePickerFinishBlock)rf_finishBlock {
return objc_getAssociatedObject(self, &kFinishBlockKey);
}
- (void)setRf_finishBlock:(RFImagePickerFinishBlock)rf_finishBlock {
self.delegate = self;
objc_setAssociatedObject(self, &kFinishBlockKey, rf_finishBlock, OBJC_ASSOCIATION_COPY_NONATOMIC);
}
#pragma mark - UIImagePickerControllerDelegate
- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary<NSString *,id> *)info
{
RFImagePickerFinishBlock block = self.rf_finishBlock;
if (block) block(info);
[self dismissViewControllerAnimated:YES completion:nil];
self.rf_finishBlock = nil;
}
@end
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使用：
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| __weak typeof(self)weakSelf = self;
UIImagePickerController *picker = [UIImagePickerController rf_imagePickerWithFinishBlock:^(NSDictionary *info) {
NSLog(@"finish picke image\n info:%@",info);
UIImage *img = info[@"UIImagePickerControllerOriginalImage"];
weakSelf.view.layer.contents = (id)img.CGImage;
}];
[self presentViewController:picker animated:YES completion:nil];
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或者
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| UIImagePickerController *picker = [[UIImagePickerController alloc] init];
__weak typeof(self)weakSelf = self;
picker.rf_finishBlock = ^(NSDictionary *info) {
NSLog(@"finish picke image\n info:%@",info);
UIImage *img = info[@"UIImagePickerControllerOriginalImage"];
weakSelf.view.layer.contentsGravity = kCAGravityResizeAspect;
weakSelf.view.layer.contents = (id)img.CGImage;
};
[self presentViewController:picker animated:YES completion:nil];
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关联一个按钮事件 block，当触发按钮 UIControlEventTouchUpInside 事件时回调。
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| @interface UIButton (RFBlcoks)
typedef void(^RFButtonClickBlock)(UIButton *button);
@property (nonatomic, copy) RFButtonClickBlock rf_buttonClickBlock;
@end
|
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| static char kButttonClickBlockKey;
@implementation UIButton (RFBlcoks)
- (RFButtonClickBlock)rf_buttonClickBlock
{
return objc_getAssociatedObject(self, &kButttonClickBlockKey);
}
- (void)setRf_buttonClickBlock:(RFButtonClickBlock)rf_buttonClickBlock
{
objc_setAssociatedObject(self, &kButttonClickBlockKey, rf_buttonClickBlock, OBJC_ASSOCIATION_COPY_NONATOMIC);
[self addTarget:self action:@selector(buttonClicked) forControlEvents:UIControlEventTouchUpInside];
}
- (void)buttonClicked
{
if (self.rf_buttonClickBlock) {
self.rf_buttonClickBlock(self);
}
}
@end
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使用：
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| self.button.rf_buttonClickBlock = ^(UIButton *button){
NSLog(@"%@ clicked",button);
};
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Demo 地址：
参考资料：