Read data from SqlDataSource or GridView

The data in the gridview can read by using FindControl property of Gridview control. For example, for reading values set in the Checkbox column in the grid.

    for (i = 0; i < GridView1.Rows.Count; i++) 

{

            CheckBox chk = (CheckBox)GridView1.Rows[i].FindControl("checkbox1");

            //here code for using value captured in chk 
}

Provided your data set isn't gigantic, you could store it in the Session, bind your GridView to the Session data, and then re-use the Session data in your other web objects.

Your code would then look something like this (you'll have to forgive any minor inaccuracies -- I'm away from my development box at the moment):

protected override OnInit(object sender, EventArgs e)
{
    base.OnInit();

    if (Page.IsPostback == false)
    {
        SetSessionData();
    }
    //
    // Set your GridView, DataTable, DataView, etc. events here.
    //
}

void SetSessionData();
{
        List<YourDataBoundObject> myDataBoundObject = GetYourDataBoundObject(); // Or Collection<T>, IEnumerable<T>, etc.
        Session["data"] = myDataBoundObject;
}

void YourGridView_Load(object sender, EventArgs e)
{
    BindYourGridView();
}

void BindYourGridView()
{
    YourGridView.DataSource = GetSessionData();
    YourGridView.DataBind();
}

List<YourDataBoundObject> GetSessionData()
{
    return (List<YourDataBoundObject>) Session["data"];
}

void YourDataTable_Load(object sender, EventArgs e)
{
    BindYourDataTable();
}

void BindYourDataTable()
{
    YourDataTable.DataSource = GetSessionData();
    YourDataTable.DataBind();
}