話不多說，同樣是個人筆記。

1、在頭文件聲明類方法
#import <Foundation/Foundation.h>

@interface Student : NSObject
+ (Student*) getInstance;
@end

2、在源文件中實(shí)現(xiàn)相應(yīng)方法

#import "Student.h"

static Student* instance = nil;

@interface Student()
- (instancetype) init;
@end

@implementation Student
+ (Student*) getInstance {
    if (instance == nil) {
        instance = [[Student alloc]init];
    }

    return instance;
}

- (instancetype) init {
    return self;
}

//覆蓋allocWithZone
+ (id) allocWithZone:(struct _NSZone *)zone {
    @synchronized(self) {
        if (!instance) {
            instance = [super allocWithZone:zone];//確保使用同一塊內(nèi)存地址
            return instance;
        }
    }

    return nil;
}

- (id) copyWithZone: (NSZone*)zone {
    return self;//確保copy對象也是唯一
}
@end

3、調(diào)用

Student* stu1 = [Student getInstance];
Student* stu2 = [Student getInstance];
Student* stu3 = [stu1 copy];
    
NSLog(@"stu1 = %@", stu1);
NSLog(@"stu2 = %@", stu2);
NSLog(@"stu3 = %@", stu3);

4、測試結(jié)果

stu1 = <Student: 0x100503920>
stu2 = <Student: 0x100503920>
stu3 = <Student: 0x100503920>