Girdview disappears while filtering

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C#

ASP

ASP.NET

C#3.5

C#5.0

ASP.NET2

, +

Hi I am using two dropdown list in my grid view and while the both dropdown list is in the "--Select-- " and "--Select--",The grid should show all the data,but for me it disappears while selecting a value in ddl before moving to the next ddl for filtering

What I have tried:

 private void BindGrid()
        {
            DataTable dt = new DataTable();
            
            string query = " select * from gvdetails17 WHERE 1=1 ";
            SqlCommand cmd = new SqlCommand();
            cmd.Connection = cn;
            if (ddlAddSalary1.SelectedValue != "")
            {
                gvDetails.Visible = false;
                string[] sal = ddlAddSalary1.SelectedValue.Split('-');
                string from = sal[0];
                string to = sal[1];


                query += " and Sal between  @fromsal and @tosal ";
                cmd.Parameters.AddWithValue("@fromsal", from);
                cmd.Parameters.AddWithValue("@tosal", to);
                
            }

            if (ddlAge.SelectedValue != "")
            {
                gvDetails.Visible = false;
                string[] age = ddlAge.SelectedValue.Split('-');
                string from1 = age[0];
                string to1 = age[1];

                query += " and Age between  @fromage and @toage ";
                cmd.Parameters.AddWithValue("@fromage", from1);
                cmd.Parameters.AddWithValue("@toage", to1);
                gvDetails.Visible = true;
                
            }
            cmd.CommandText = query;
            
            cmd.CommandType = CommandType.Text;
            SqlDataAdapter da = new SqlDataAdapter(cmd);
            da.Fill(dt);
            gvDetails.DataSource = dt;
            gvDetails.DataBind();

        }
protected void ddlAddSalary1_SelectedIndexChanged1(object sender, EventArgs e)
        {
            
            BindGrid();
        }

protected void ddlAge_SelectedIndexChanged(object sender, EventArgs e)
        {
           

            BindGrid();
        }