title: Dynamic change dropdownlist and textbox by custom control
body: <p>I want to write a custom control involving a <code>DropDownList</code> and a <code>TextBox</code>.
  Actually,  I want to dynamically render <code>DropDownList</code> and  <code>TextBox</code>.
  For example: when a user clicks a <code>Checkbox</code>, the <code>Textbox</code> will change to a <code>DropdownList</code>. On the other hand, when a user deselects the <code>Checkbox</code>, the <code>Dropdownlist</code> will change to a <code>Textbox</code>.</p>
  
  <p>I know this can be done using two controls, which sets the visibility for both control. But can I do it on a custom control?</p>