ASP: My data field is null since the 2nd Page_Load()
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My code_behind is:

    public partial class Question2 : System.Web.UI.Page
    {
        private SqlDataAdapter dataAdapter;
        private DataTable table;

        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                table = new DataTable();
                //And pull the data from my DB to the table
            }
        }

I am intend to store my data (the 'table') in the class's field BUT after I clicked on any button of my page. I found that the Page_Load() is called again and my all data fields has gone. They're 'null'.

I'm really confuse what happen O_O. I just needed to store my table for later use. But why they're lost ? When does it lost ? Please help, Thank you.