實現單例,首先遵循NSCopy協議(遵循協議是為了重寫協議中的方法)

• 在MRC下的示例代碼:

#import "AudioTools.h"

@implementation AudioTools

static id _instanceType = nil;
// 自定義類方法創建單例
+(instancetype)sharadAudioTools{
    //一次性執行實現單例
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _instanceType = [[self alloc]init];
    });
    return _instanceType;
}
// 嚴謹寫法需要重寫此方法,避免alloc]init或new實例化新對象
+ (instancetype)allocWithZone:(struct _NSZone *)zone{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _instanceType = [super allocWithZone:zone];
    });
    return _instanceType;
}
// 防止對象Copy操作 (一般此方法默認只對NSString類型有效)
-(id)copyWithZone:(NSZone *)zone{
    return _instanceType;
}
//MRC下防止手動銷毀對象(重寫后不執行任何操作)
-(oneway void)release{
    
}

//以下為其他引用計數器操作方法
-(instancetype)retain{
    return _instanceType;
}
-(instancetype)autorelease{
    return _instanceType;
}
- (NSUInteger)retainCount{
    return 1;
}
@end

• 在ARC下示例代碼:

#import "NetWorkTools.h"

@implementation NetWorkTools
static id _instanceType = nil;
//自定義類方法
+(instancetype)sharadNetWorkTools{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _instanceType = [[self alloc]init];
    });
    return _instanceType;
}
//重寫父類方法,防止通過alloc]init或new的方式開辟新空間
+ (instancetype)allocWithZone:(struct _NSZone *)zone{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _instanceType = [super allocWithZone:zone];
    });
    return _instanceType;
}
//防止對象copy操作
-(id)copyWithZone:(NSZone *)zone{
    return _instanceType;
}
@end