Points to remember while creating composite controls

1. Get the ClientID of the control created and attach that ID to the child controls ID as well ClientInstanceName.

Sample Code in C#
public class NewControl : CompositeControl
{
ASPxTextBox txtTest;
protected override void CreateChildControls()
{
txtTest = new ASPxText();
txtTest.ID = "txtTest" + this.ClientID;
txtTest.ClientInstanceName = "txtTest" + this.ClientID;
txtTest.Text = “Control Initialized”;
}
}
this.Controls.Add(txtTest);
2. All controls that are interactive (i.e. not standard HTML code) created in CreateChildControls().

3. When you use popup control inside a composite control, use popup control’s Show/Popup client side events to render the controls and change contents.
strScript = cbPanelID + ".PerformCallback ('Binding');";
pcComments.ClientSideEvents.PopUp = string.Format ("function(s,e) {{{0}}}", strScript);
void cbPanel_Callback(object source, DevExpress.Web.ASPxClasses.CallbackEventArgsBase e)
{
// Write codes here to perform action while loading the control
}
We are calling the Callback panels (cbPanelID) PerformCallback client side event when popup window (pcComments) populated.