cocos2d 怎么实现两个动作执行完之后执行第三个

Cocos2d-x
#1

CCAction* ac1 = …

CCAction* ac2 = …

CCAction* ac3 = …

现在的需求时ac1和ac2同时执行，都执行完之后执行ac3怎么搞｀｀｀？

#2

CCSequence::createWithTwoActions( CCSpawn::create(ac1, ac2), ac3);