Question: I'm wondering if it is possible to use the OpenCV framework to recognise a building? 
For example, if I store an image of a building, is it possible to use OpenCV to detect this building through the iPhone camera?

Thanks!

Answer: 
```
protected void ddl_UOM_SelectedIndexChanged(object sender, EventArgs e)
{

    string uom_Name = ddl_UOM.SelectedItem.Value;
    ddl_UOM2.Items.Clear();
    ddl_UOM3.Items.Clear();
    ddl_UOM4.Items.Clear();

    ddl_UOM2.Items.Add(uom_Name);
    ddl_UOM3.Items.Add(uom_Name);
    ddl_UOM4.Items.Add(uom_Name);

}

```

After writing code in ddl\_UOM\_SelectedIndexChanged() , call ddl\_UOM\_SelectedIndexChanged() method from Page\_Load()

```
        protected void Page_Load(object sender, EventArgs e)
        {
         try
         {
          if (!IsPostBack)
           {
                   ddl_UOM_SelectedIndexChanged(sender, e );
           }

         }
       catch (Exception)
       {

        throw;
       }
     }

```
You have to set AutoPostBack="true" to the first drop down list and clear other drop downs items before adding new item.

**ASPX:**

```
<asp:DropDownList ID="ddl_UOM" runat="server" OnSelectedIndexChanged="ddl_UOM_SelectedIndexChanged" AutoPostBack="true">
        <asp:ListItem Text="Amount" Value="Amount"></asp:ListItem>
        <asp:ListItem Text="PAC" Value="PAC"></asp:ListItem>
        <asp:ListItem Text="Base" Value="Base"></asp:ListItem>
</asp:DropDownList>
<asp:DropDownList ID="ddl_UOM2" runat="server"></asp:DropDownList>
<asp:DropDownList ID="ddl_UOM3" runat="server"></asp:DropDownList>
<asp:DropDownList ID="ddl_UOM4" runat="server"></asp:DropDownList>

```

**ASPX.CS**

```
protected void ddl_UOM_SelectedIndexChanged(object sender, EventArgs e)
    {
        string uom_Name = ddl_UOM.SelectedItem.Value;
        ddl_UOM2.Items.Clear();
        ddl_UOM2.Items.Add(new ListItem(uom_Name, uom_Name));

        ddl_UOM3.Items.Clear();
        ddl_UOM3.Items.Add(new ListItem(uom_Name, uom_Name));

        ddl_UOM4.Items.Clear();
        ddl_UOM4.Items.Add(new ListItem(uom_Name, uom_Name));
    }

```