事件 event Action

public class A
{
    public event Action OnStateChanged;
}

public class B
{
    public A Stage;
    public event Action OnXXStageChanged
    {
        add 
        {
            if(Stage != null){
                Stage.OnStateChanged += value;
            }
        }
        remove
        {
            if(Stage != null){
                Stage.OnStateChanged -= value;
            }
        }
    }

    
}

public class C
{
    void test()
    {
        B b = new B();
        b.OnXXStageChanged += f;
        b.OnXXStageChanged -= f;
    }

    void f()
    {

    }
}

这么做的目的是可以把A中的时间封装起来