可以在iOS中实现Singleton继承

Question

我有几个应该从某个A类继承的类.

他们每个人都应该是一个单身人士.

这可以实现吗？

Answer 1

Singleton-pattern的这种实现允许继承:

+ (instancetype)sharedInstance {

    static dispatch_once_t once;
    static NSMutableDictionary *sharedInstances;

    dispatch_once(&once, ^{ /* This code fires only once */

        // Creating of the container for shared instances for different classes
        sharedInstances = [NSMutableDictionary new];
    });

    id sharedInstance;

    @synchronized(self) { /* Critical section for Singleton-behavior */

        // Getting of the shared instance for exact class
        sharedInstance = sharedInstances[NSStringFromClass(self)];

        if (!sharedInstance) {
            // Creating of the shared instance if it's not created yet
            sharedInstance = [self new];
            sharedInstances[NSStringFromClass(self)] = sharedInstance;
        }
    }

    return sharedInstance;
}