一位開發(fā)前輩玉令天下的博客里對(duì)單例的介紹很不錯(cuò)澜驮，原文iOS的單例模式在這里作兩點(diǎn)補(bǔ)充昭雌。
- 即使用GCD的dispatch_once 創(chuàng)建的單例图毕，最好還是遵循<NSCopying,NSMutableCopying>的協(xié)議盹舞，并實(shí)現(xiàn)相應(yīng)的方法叙量，防止別人誤調(diào)copy方法而崩潰
在這里我寫了個(gè)demo
Singleton.h文件如下
#import <Foundation/Foundation.h>
@interface Singleton : NSObject
+(instancetype) shareInstance;
@property (copy, nonatomic) NSString *name;
@property (copy, nonatomic) NSString *title;
@end
Singleton.m文件如下
#import "Singleton.h"
@interface Singleton () <NSCopying,NSMutableCopying>
@end
@implementation Singleton
static Singleton* _instance = nil;
+(instancetype) shareInstance {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
_instance = [[super allocWithZone:NULL] init];//調(diào)用[[super allocWithZone:NULL] init],因?yàn)楸绢愐呀?jīng)重載allocWithZone基本的對(duì)象分配方法,要借用父類(NSObject)的功能來幫助處理底層內(nèi)存分配
_instance.name = @"";
_instance.title = @"";
});
return _instance;
}
+(id)allocWithZone:(struct _NSZone *)zone {
// return [Singleton shareInstance];
return _instance;//兩種寫法效果是一樣的
}
- (id)copyWithZone:(nullable NSZone *)zone {
// return [Singleton shareInstance];
return _instance;
}
- (id)mutableCopyWithZone:(nullable NSZone *)zone {
// return [Singleton shareInstance];
return _instance;
}
- (NSString *)description {
return [NSString stringWithFormat:@"_name====%@,_title=====%@",_name,_title];
}
測(cè)試方法如下
- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
Singleton *singleton = [Singleton shareInstance];
singleton.name = @"singleton";
singleton.title = @"singletonDesc";
NSLog(@"singleton------%p,description------%@",singleton,singleton);
Singleton *singletonCopy = [singleton copy];
NSLog(@"singletonCopy------%p,description------%@",singletonCopy,singletonCopy);
Singleton *singletonMutableCopy = [singleton mutableCopy];
NSLog(@"singletonMutableCopy------%p,description------%@",singletonMutableCopy,singletonMutableCopy);
Singleton *singletonShareInstanceAgain = [Singleton shareInstance];
NSLog(@"singletonShareInstanceAgain------%p,singletonShareInstanceAgain------%@",singletonShareInstanceAgain,singletonShareInstanceAgain);
Singleton *singletonAlloc = [[Singleton alloc] init];
NSLog(@"singletonAlloc------%p,description------%@",singletonAlloc,singletonAlloc);
}
打印結(jié)果如下
2018-08-15 15:00:31.441223+0800 SingletonTest[65282:7781841] singleton------0x60400042c800,description------_name====singleton,_title=====singletonDesc
2018-08-15 15:00:31.441499+0800 SingletonTest[65282:7781841] singletonCopy------0x60400042c800,description------_name====singleton,_title=====singletonDesc
2018-08-15 15:00:31.441726+0800 SingletonTest[65282:7781841] singletonMutableCopy------0x60400042c800,description------_name====singleton,_title=====singletonDesc
2018-08-15 15:00:31.441855+0800 SingletonTest[65282:7781841] singletonShareInstanceAgain------0x60400042c800,singletonShareInstanceAgain------_name====singleton,_title=====singletonDesc
2018-08-15 15:00:31.442457+0800 SingletonTest[65282:7781841] singletonAlloc------0x60400042c800,description------_name====singleton,_title=====singletonDesc
可以看出shareInstance倡蝙、copy、mutableCopy绞佩、alloc創(chuàng)建出來是同一個(gè)單例寺鸥，內(nèi)存地址相同
- 單例對(duì)象的釋放：在所有使用該單例的對(duì)象都釋放后，單例對(duì)象本身也會(huì)自己釋放 原文地址
+(instancetype)shareInstance {
static __weak SingletonClass *instance;
SingletonClass *strongInstance = instance;
@synchronized(self) {
if (strongInstance == nil) {
strongInstance = [[[self class] alloc] init];
instance = strongInstance;
}
}
return strongInstance;
}
寫了個(gè)demo驗(yàn)證了品山，這樣創(chuàng)建的單例確實(shí)會(huì)隨著持有對(duì)象的銷毀而銷毀
2018-08-15 15:45:26.197552+0800 SingletonTest[65879:7837310] instanceAddress=0x600000000ef0,_content====the VC Hold Instance
2018-08-15 15:45:28.625037+0800 SingletonTest[65879:7837310] instanceAddress=0x600000000f10,_content====the Instance after VC dealloc Information
大概的思路是胆建，從A控制器進(jìn)入B控制器，B控制器創(chuàng)建一個(gè)單例肘交，打印此單例的信息笆载，然后B控制器回到A控制器，在A控制器創(chuàng)建單例并打印單例的信息涯呻，兩次打印的信息對(duì)比地址不同凉驻。
如果有錯(cuò)誤的地方，歡迎指正复罐。
