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设计一个不强引用对象的单例字典
设计一个不强引用对象的单例字典
大家都知道,使用NSDictionary存储对象的时候会强引用对象,导致被存储对象的引用计数+1,有时候,我们想用单例来存储对象,但又不希望强引用存储的对象,这该怎么实现呢?
在这里,我们可以使用NSMapTable来实现这个功能.
我直接给出源码:
WeakDictionary.h + WeakDictionary.m
//// WeakDictionary.h// 弱引用字典//// http://www.cnblogs.com/YouXianMing/// Copyright (c) 2014年 Y.X. All rights reserved.//#import <Foundation/Foundation.h>#define GET_WEAK_OBJECT(key) [WeakDictionary objectForKey:(key)]#define REGISTER_WEAK_OBJECT(object, key) [WeakDictionary addObject:(object) forKey:(key)]@interface WeakDictionary : NSObject+ (void)addObject:(id)object forKey:(NSString *)key;+ (id)objectForKey:(NSString *)key;@end
//// WeakDictionary.m// 弱引用字典//// http://www.cnblogs.com/YouXianMing/// Copyright (c) 2014年 Y.X. All rights reserved.//#import "WeakDictionary.h"static NSMapTable *weakDictionary = nil;@implementation WeakDictionary+ (void)initialize{ if (self == [WeakDictionary class]) { // 强引用key值弱引用object weakDictionary = [NSMapTable strongToWeakObjectsMapTable]; }}+ (void)addObject:(id)object forKey:(NSString *)key{ if (object == nil || key == nil) { NSLog(@"object & key should not be nil."); return; } if ([weakDictionary objectForKey:key] == nil) { [weakDictionary setObject:object forKey:key]; }}+ (id)objectForKey:(NSString *)key{ return [weakDictionary objectForKey:key];}@end
测试代码:
//// AppDelegate.m// WeakDic//// Copyright (c) 2014年 Y.X. All rights reserved.//#import "AppDelegate.h"#import "WeakDictionary.h"#import "YXGCD.h"#import "Model.h"@interface AppDelegate ()@property (nonatomic, strong) Model *model;@property (nonatomic, strong) GCDTimer *timer;@end@implementation AppDelegate- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions{ // 创建临时model Model *tmp = [Model new]; // 注册弱引用对象 REGISTER_WEAK_OBJECT(tmp, @"Model"); // 通过属性持有这个临时model self.model = tmp; // 7s之后这个属性持有另外一个model(原先model被释放了) [[GCDQueue mainQueue] execute:^{ self.model = [Model new]; } afterDelay:NSEC_PER_SEC*7]; // 启动定时器监测临时model _timer = [[GCDTimer alloc] initInQueue:[GCDQueue mainQueue]]; [_timer event:^{ NSLog(@"%@", GET_WEAK_OBJECT(@"Model")); } timeInterval:NSEC_PER_SEC]; [_timer start]; return YES;}@end
测试图例:
至于为何要设计出这么一种单例出来,这种不增加对象引用计数却能持有对象的单例,你想想能有什么用处呢:)
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