List <subclass> List <parent class> errors

Record the mistakes made by new users for future reference.

There are two classes

1 public class A2 {3 Public string name {Get; set;} 4} 5 6 public class B: A7 {8 Public int age {Get; set;} 9}

There is a method that requires Class B age as the condition, and finally returns the set of parent Class.

1 public list <A> getabyage (INT age) 2 {3 // method body 4}

In my mind, B is a subclass of A, and you can directly return list <B>, but it doesn't actually work. So I began to find the cause and found that the original idea had a problem.

This is the case. Although a is a subclass of B, the actual types of list <A> and list <B> are both list <t>, A and B are only generic objects of the List <t> object. Therefore, direct return is definitely not feasible. Strong conversion is naturally problematic. How can this problem be solved? The experts told me that the list already provides this conversion method.

For example, if B is an object of the List <B> type, you can use B. Cast <A> (). tolist (); to convert it to a list <A> object.

In addition, I also found that you can write list <A> A = new list <A> (B) In this way. I did not test this method. You can try it. It should also work.

List <subclass> List <parent class> errors