<asp:DropDownList ID="cmbPrueba" runat="server" OnSelectedIndexChanged="cmbPrueba_SelectedIndexChanged" AutoPostBack="true">
    <asp:ListItem Value="0">Compresor de Aire</asp:ListItem>
    <asp:ListItem Value="1">Compresor/Unidad de Refrigeración</asp:ListItem>
</asp:DropDownList>
<asp:Button ID="btnActualizar" runat="server" Text="Actualizar" OnClick="btnActualizar_Click" />
<asp:PlaceHolder ID="PlaceHolder1" runat="server"></asp:PlaceHolder>

private string[] CompresorUnidadDeRefrigeracionTipoCompresor = new string[] { "Compresor Alternativo", "Compresor de Tornillo", "Unidad de Refrigeración" };

public partial class Controles : System.Web.UI.Page
{
    private Label _Label;
    private TextBox _TextBox = new TextBox();
    private Calendar _Calendar = new Calendar();
    private DropDownList _DropDownList = new DropDownList();

    private string[] CompresorDeAire = new string[] { "TextBox", "Calendar", "TextBox" };
    private string[] CompresorUnidadDeRefrigeracion = new string[] { "DropDownList", "TextBox", "Calendar", "Calendar", "TextBox" };
    private string[] CompresorUnidadDeRefrigeracionTipoCompresor = new string[] { "Compresor Alternativo", "Compresor de Tornillo", "Unidad de Refrigeración" };
    private string[] BombaElectrica = new string[] { "TextBox", "TextBox", "TextBox", "TextBox", "TextBox", "TextBox" };

    protected void Page_Load(object sender, EventArgs e)
    {
       LoadInfo(CompresorDeAire);
    }

    private void LoadInfo(string[] Arreglo)
    {
        for (int i = 0; i < Arreglo.Length; i++)
        {
            _Label = new Label();
            _TextBox = new TextBox();
            _Calendar = new Calendar();
            _DropDownList = new DropDownList();

            _Label.Text = Arreglo[i].ToString() + i.ToString();
            _Label.ID = _Label.Text;
            PlaceHolder1.Controls.Add(_Label);
            PlaceHolder1.Controls.Add(new LiteralControl("<br />"));

            if (Arreglo[i] == _TextBox.GetType().Name.ToString())
            {
                _TextBox.ID = "txt" + _Label.ID;
                //_TextBox.AutoPostBack = true;
                PlaceHolder1.Controls.Add(_TextBox);
            }
            else if (Arreglo[i] == _Calendar.GetType().Name.ToString())
            {
                _Calendar.ID = "cln" + _Label.ID;
                PlaceHolder1.Controls.Add(_Calendar);
            }
            else if (Arreglo[i] == _DropDownList.GetType().Name.ToString())
            {
                _DropDownList.ID = "cmb" + _Label.ID;

                //_DropDownList.AutoPostBack = true;
                foreach (var item in CompresorUnidadDeRefrigeracionTipoCompresor)
                {
                    int j = 0;
                    _DropDownList.Items.Add(item);
                    j++;
                }

                PlaceHolder1.Controls.Add(_DropDownList);
            }

            PlaceHolder1.Controls.Add(new LiteralControl("<br /><br />"));
        }
    }

    protected void cmbPrueba_SelectedIndexChanged(object sender, EventArgs e)
    {
        txtMensaje.Text = "";
        PlaceHolder1.Controls.Clear();

        switch (cmbPrueba.SelectedIndex)
        {
            case 0:
                this.LoadInfo(CompresorDeAire);
                break;

            case 1:
                this.LoadInfo(CompresorUnidadDeRefrigeracion);
                break;

            case 2:
                this.LoadInfo(BombaElectrica);
                break;
        }
    }

    protected void btnActualizar_Click(object sender, EventArgs e)
    {
        txtMensaje.Text = "";

        for (int i = 0; i < PlaceHolder1.Controls.Count; i++)
        {
            switch (PlaceHolder1.Controls[i].GetType().Name.ToString())
            {
                case "TextBox":
                    TextBox TB = PlaceHolder1.FindControl(PlaceHolder1.Controls[i].ID) as TextBox;
                    txtMensaje.Text += PlaceHolder1.Controls[i].GetType().Name + " " + PlaceHolder1.Controls[i].ID + " " + TB.Text + "n";
                    TB.Text += "*";

                    break;

                case "Calendar":
                    Calendar Cal = PlaceHolder1.FindControl(PlaceHolder1.Controls[i].ID) as Calendar;
                    txtMensaje.Text += PlaceHolder1.Controls[i].GetType().Name + " " + PlaceHolder1.Controls[i].ID + " " + Cal.SelectedDate.ToShortDateString() + "n";
                    break;

                case "DropDownList":
                    DropDownList DD = PlaceHolder1.FindControl(PlaceHolder1.Controls[i].ID) as DropDownList;

                    txtMensaje.Text += PlaceHolder1.Controls[i].GetType().Name + " " + PlaceHolder1.Controls[i].ID + " " + DD.Text + "n";
                    break;
            }
        }
    }

    protected void btnLimpiar_Click(object sender, EventArgs e)
    {
        PlaceHolder1.Controls.Clear();
        txtMensaje.Text = "";
    }
}