[alessam4pro]

جرب هذا
private void SearchBox_TextChanged(object sender, EventArgs e)
{
    if (ComboBox1.SelectedIndex == 0)
    {
        con = new SqlConnection(cs);
        con.Open();
        DataTable DT = new DataTable();
        SqlClient.SqlDataAdapter DA = new SqlClient.SqlDataAdapter();
        DT.Clear();
        DA = new SqlClient.SqlDataAdapter("SELECT * FROM SalesInvoice WHERE State ='TRUE' AND  InvoiceCode = '" + SearchBox.Text + "'", con);
        DA.Fill(DT);
        dgv.DataSource = DT.DefaultView;
    }
    if (ComboBox1.SelectedIndex == 1)
    {
        con = new SqlConnection(cs);
        con.Open();
        DataTable DT = new DataTable();
        SqlClient.SqlDataAdapter DA = new SqlClient.SqlDataAdapter();
        DT.Clear();
        DA = new SqlClient.SqlDataAdapter("SELECT * FROM SalesInvoice WHERE  State ='TRUE' AND CustomerName = '" + SearchBox.Text + "'", con);
        DA.Fill(DT);
        dgv.DataSource = DT.DefaultView;
    }
}