Wrong ClientID for dynamically added child control

Question

I am trying to rework asp.net usercontrol with .ascx markup to WebControl(only .cs).

In my_new_webcontrol.cs I have:

private readonly DropDownList _source = new DropDownList();

protected override void OnInit(EventArgs e)
{
    base.OnInit(e);
    _source.ID = String.Format("{0}{1}{2}", ID, IdSeparator, "Source");
    Controls.Add(_source);
}

protected override void Render(HtmlTextWriter writer)
{
    RenderContents(writer);
}

protected override void RenderContents(HtmlTextWriter writer)
{
    _source.RenderControl(writer);
}

Problem is that it generates DropDownList with id="MainContent_ComboBox1$Source" and name="ctl00$MainContent$ComboBox1$Source". Name generated as expected but Id wrong and here should be _ instead of $.

How I can achieve id="MainContent_ComboBox1_Source" and name="ctl00$MainContent$ComboBox1$Source".

Update 1.

Tried to put DropDownList into Panel as Knaģis suggested:

private readonly DropDownList _source = new DropDownList();
private readonly Panel _panel = new Panel();

protected override void OnInit(EventArgs e)
{
    base.OnInit(e);
    _panel.ID = ID;
    _panel.Controls.Add(_source);
    Controls.Add(_panel);
}

protected override void Render(HtmlTextWriter writer)
{
    RenderContents(writer);
}

protected override void RenderContents(HtmlTextWriter writer)
{
    _panel.RenderControl(writer);
}

No success. Generated HTML(ComboBox1 in id and name missing):

<div id="MainContent_ComboBox1">
    <select name="ctl00$MainContent$Source" onchange="javascript:setTimeout('__doPostBack(\'ctl00$MainContent$Source\',\'\')', 0)" id="MainContent_Source"></select>    
</div>

Answer

As Knaģis suggested I missed INamingContainer in my server control class declaration

public class ComboBox: WebControl, INamingContainer

Answer 1

You should add a child panel (or another container control) with ID of ComboBox1 and then within that add your DropDownList with ID of Source. Let the ASP.NET generate the hierarchical identifiers.

In short - if you want to preserve the values of ClientID and Name for your reworked control, you should use the exact same control tree as your .ascx markup.