ios - 避免在 Objective-C 中滥用单例

Question

我创建了一个单例:

+(instancetype)allocWithZone:(struct _NSZone *)zone
{
    NSAssert(FALSE, @"Please use getSharedInstance class method of MotionManager to avoid singleton abuse. =)");

    return nil;
}


+ (id) getSharedInstance
{
    if (!instance)
    {
        instance = [[super allocWithZone:NULL] init];
    }

    return instance;
}

为什么上面的工作正常，但下面的抛出异常？

+(instancetype)allocWithZone:(struct _NSZone *)zone
{
    NSAssert(FALSE, @"Please use getSharedInstance class method of MotionManager to avoid singleton abuse. =)");

    return nil;
}


+ (id) getSharedInstance
{
    if (!instance)
    {
        instance = [[super alloc] init];
    }

    return instance;
}

Answer 1

这是创建单例的正确方法:

+ (id)sharedManager {


    static Singleton *sharedManager = nil;
    static dispatch_once_t onceToken;

    dispatch_once(&onceToken, ^{

        sharedMyManager = [[self alloc] init];

    });

    return sharedManager;
}