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;
       }
     }

```
May be you don't have set **AutoPostBack** property to **true**. Try below code sample : 

**ASPX:**

```
<asp:DropDownList runat="server" ID="parentDropDown" OnSelectedIndexChanged="parentDropDown_SelectedIndexChanged" AutoPostBack="true">
    <asp:ListItem Text="1" Value="1"></asp:ListItem>
    <asp:ListItem Text="2" Value="2"></asp:ListItem>
    <asp:ListItem Text="3" Value="3"></asp:ListItem>
</asp:DropDownList>
<asp:DropDownList runat="server" ID="child1">
</asp:DropDownList>
<asp:DropDownList runat="server" ID="child2">
</asp:DropDownList>

```

**Code Behind:**

```
protected void parentDropDown_SelectedIndexChanged(object sender, EventArgs e)
{
    string uom_Name = parentDropDown.SelectedValue;
    child1.Items.Add(uom_Name);
    child2.Items.Add(uom_Name);
}

```

**If you want to remove existing item from child before you add then:**

```
protected void parentDropDown_SelectedIndexChanged(object sender, EventArgs e)
{
    string uom_Name = parentDropDown.SelectedValue;

    child1.Items.Clear();
    child2.Items.Clear();

    child1.Items.Add(uom_Name);
    child2.Items.Add(uom_Name);
}

```