C# - OnSelectedIndexChanged Don't Seem To Work

What I would like to do is:

From a textbox, I add a name for a product and create a object with that name.

The product object is then added to a Dictionary.

Then, I want to bind this Dictionary to a dropdown list.

If I change the selected item, I want to display the number of the chosen product (Default as 0 when I create the product object).

The problem is that when I try to change the item in the dropdown list, nothing happens.

.aspx
<asp:TextBox ID="productText" runat="server"></asp:TextBox>
<asp:Button ID="newProductButton" runat="server" OnClick="newProduct_Click" />
<div>
<asp:DropDownList ID="ddlProducts" runat="server" AutoPostBack="true"

[Code]....