How to solve Object reference not set to an instance of an object.? [duplicate]
You need to initialize the list first:
protected List<string> list = new List<string>();
I think you just need;
List<string> list = new List<string>();
list.Add("hai");
There is a difference between
List<string> list;
and
List<string> list = new List<string>();
When you didn't use new keyword in this case, your list didn't initialized. And when you try to add it hai, obviously you get an error.