iOS 单例模式单独调用alloc 、 copy、mutableCopy依然为单例

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！