Get the value of Selected Row From Gridview

//Just Before the page load define the variable
string textBoxCompanyName, textBoxContactName, textBoxCustomerID;
//Then on the button click event get the values from the grid
//Here dvCustomerDetail is the name of a Gridview
foreach (GridViewRow row in dvCustomerDetail.Rows)
{
textBoxCustomerID = ((TextBox)row.FindControl("tbxCustomerID")).Text;
textBoxCompanyName = ((TextBox)row.FindControl("tbxCompanyName")).Text;
textBoxContactName = ((TextBox)row.FindControl("tbxContactName")).Text;
}