有时我们需要在一个对象生命周期结束的时候触发一个操作,希望当该对象dealloc的时候调用一个外部指定的block,但又不希望直接hook dealloc方法,这样侵入性太强了.下面贴一段非常简单的实现方式,通过一个category给外部暴露一个block注入的接口,内部将该block封装到一个寄生对象中(Parasite),该寄生对象在dealoc的时候触发block调用,所有的寄生对象通过runtime的AssociatedObject机制与宿主共存亡,从而达到监控宿主生命周期的目的.
注意事项
- block触发的线程与对象释放时的线程一致,请注意后续操作的线程安全.
- 不要在block中强引用对象,否则引用循环释放不了;
- 不要在block中通过weak引用对象,因为此时会返回nil;
(根据WWDC2011,Session322对对象释放时间的描述，associated objects清除在对象生命周期中很晚才执行，通过被NSObject -dealloc方法调用的object_dispose()函数完成);
NSObject+Guard.h
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#import <Foundation/Foundation.h> @interface NSObject (Guard) /** @brief 添加一个block,当该对象释放时被调用 **/- (void)guard_addDeallocBlock:(void(^)(void))block; @end |
NSObject+Guard.m
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#import "NSObject+Guard.h"#import <objc/runtime.h>
@interface Parasite : NSObject@property (nonatomic, copy) void(^deallocBlock)(void);@end
@implementation Parasite
- (void)dealloc { if (self.deallocBlock) { self.deallocBlock(); }}
@end
@implementation NSObject (Guard)
- (void)guard_addDeallocBlock:(void(^)(void))block { @synchronized (self) { static NSString *kAssociatedKey = nil; NSMutableArray *parasiteList = objc_getAssociatedObject(self, &kAssociatedKey); if (!parasiteList) { parasiteList = [NSMutableArray new]; objc_setAssociatedObject(self, &kAssociatedKey, parasiteList, OBJC_ASSOCIATION_RETAIN_NONATOMIC); } Parasite *parasite = [Parasite new]; parasite.deallocBlock = block; [parasiteList addObject: parasite]; }}
@end
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时间： 2024-10-10 04:08:27