c# - How to solve Object reference not set to an instance of an object.?

In my asp.net program.I set one protected list.And i add a value in list.But it shows Object reference not set to an instance of an object error

protected List list;
protected void Page_Load(object sender, EventArgs e)
{
     list.Add("hai");
}

How to solve this error?

Answer

You need to initialize the list first:

protected List list = new List();