怎么使泛型类创建带参数和不带参数的构造方法

带参数:

public A For<A>(Action<A> propertySpecifier,ViewPage page) where A : T
        {
            A t=(A)Activator.CreateInstance(typeof(A), page);
            propertySpecifier(t);
            _columns.Add(t);
            return t;
        }

不带参数:

        public A For<A>(Action<A> propertySpecifier) where A : T,new()
        {
            A t = new A();
            propertySpecifier(t);

            _columns.Add(t);
            return t;
        }