重温-单例模式

1 #import <Foundation/Foundation.h>
2 
3 @interface SoundTool : NSObject <NSCopying>
4 
5 + (instancetype)shareSoundTool;
6 
7 @end

#import "SoundTool.h"

@implementation SoundTool

static id _instance = nil;

+ (instancetype)allocWithZone:(struct _NSZone *)zone
{
    if (_instance == nil) {
        static dispatch_once_t onceToken;
        dispatch_once(&onceToken, ^{
            _instance = [super allocWithZone:zone];
        });
    }
    return _instance;
}

+ (instancetype)shareSoundTool
{
    return [[self alloc] init];
}

- (instancetype)init
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _instance = [super init];
    });
    return _instance;
}

+ (instancetype)copyWithZone:(struct _NSZone *)zone
{
    return _instance;
}

+ (instancetype)mutableCopyWithZone:(struct _NSZone *)zone
{
    return _instance;
}

//以下三个为非ARC使用
- (oneway void)release
{
}

- (instancetype)retain
{
    return _instance;
}

- (NSUInteger)retainCount
{
    return 1;
}