objc中的单例模式，如何保持init私有?

问题描述

我如何确保用户不调用init，而是客户端应调用sharedSingleton来获取共享实例.

How can i make sure user do not call init, instead client should call sharedSingleton to get a shared instance.

@synthesize delegate;

- (id)init
{
    self = [super init];
    if (self) {
        // Initialization code here.
    }

    return self;
}

+ (LoginController *)sharedSingleton
{
    static LoginController *sharedSingleton;

    @synchronized(self)
    {
        if (!sharedSingleton)
            sharedSingleton = [[LoginController alloc] init];
        CdtMiscRegisterConnectionChangeListenerObjc(test_ConnectionChangeListenerCallback);
        return sharedSingleton;
    }
}

推荐答案

使用UNAVAILABLE_ATTRIBUTE取消init方法，并实现initPrivate

Use UNAVAILABLE_ATTRIBUTE abolish init method, and implement initPrivate

+ (instancetype)shareInstance;

- (instancetype)init UNAVAILABLE_ATTRIBUTE;
+ (instancetype)new UNAVAILABLE_ATTRIBUTE;

实现

+ (instancetype)shareInstance {
    static MyClass *shareInstance = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        shareInstance = [[super allocWithZone:NULL] initPrivate];
    });
    return shareInstance;
}

- (instancetype)initPrivate {
    self = [super init];
    if (self) {

    }
    return self;
}

//  MARK: Rewrite
+ (id)allocWithZone:(struct _NSZone *)zone {
    return [MyClass shareInstance];
}

- (id)copyWithZone:(NSZone *)zone
{
    return self;
}

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