原文地址:https://blog.csdn.net/qqMCY/article/details/88648000
我们先写一个单例看看输出结果
+ (instancetype)sharedInstance {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
instance = [[SingleClass alloc] init];
});
return instance;
}
SingleClass *s = [SingleClass sharedInstance];
NSLog(@"instance = %@",s);
SingleClass *s1 = [[SingleClass alloc] init];
NSLog(@"alloc = %@",s1);
2019-03-18 19:28:44.154112+0800 iOSInterView[53475:185753] instance = <SingleClass: 0x600001e32bb0>
2019-03-18 19:28:44.154402+0800 iOSInterView[53475:185753] alloc = <SingleClass: 0x600001e25460>
会发现此时并不能保证在单独调用alloc方法依然单例,解决方法
#import "SingleClass.h"
static SingleClass *instance = nil;
@interface SingleClass() <NSCopying,NSMutableCopying>
@end
@implementation SingleClass
+ (instancetype)sharedInstance {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
instance = [[SingleClass alloc] init];
});
return instance;
}
// alloc 方法调用
+ (instancetype)allocWithZone:(struct _NSZone *)zone {
if (instance == nil) {
instance = [super allocWithZone:zone];
}
return instance;
}
// copy方法调用
- (instancetype)copyWithZone:(NSZone *)zone {
return self;
}
// mutableCopy 方法调用
- (instancetype)mutableCopyWithZone:(NSZone *)zone {
return self;
}
@end
SingleClass *s = [SingleClass sharedInstance];
NSLog(@"instance = %@",s);
SingleClass *s1 = [[SingleClass alloc] init];
NSLog(@"alloc = %@",s1);
SingleClass *sc = [s1 copy];
NSLog(@"%@",sc);
SingleClass *smc = [s1 mutableCopy];
NSLog(@"%@",smc);
2019-03-18 19:32:22.923938+0800 iOSInterView[54556:189354] instance = <SingleClass: 0x600001f46e00>
2019-03-18 19:32:22.924107+0800 iOSInterView[54556:189354] alloc = <SingleClass: 0x600001f46e00>
2019-03-18 19:32:22.924214+0800 iOSInterView[54556:189354] <SingleClass: 0x600001f46e00>
2019-03-18 19:32:22.924302+0800 iOSInterView[54556:189354] <SingleClass: 0x600001f46e00>
明白了吧!