Q:

How can I clear data in a GridView?

I have 3 GridViews in my page.
Using the SelectedIndexChanged event I put GridView2 and GridView3 data in GridView1
but when I restart my application GridView1 data is still persisted in browser.
I used a session variable to store the data. How can I clear GridView1

A:

You can try to clear the GridView1 itself every time you start the application:
protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                GridView1.DataSource = null;
                GridView1.DataBind();
            }

        }

