How to use two user controls as Master -Details.

Hi,
I have 2 User Controls already created now I want to use one as Master User Control and another as Details User control as follows
1 Parent Control
1.1 - USer Control 1 as Master Control
1.2 - User Control 2 as Details Control

The Master Control has the List box where I select the name of the Item and the Details Control Displays the all the available Items in stock.
I have Added ItemId in the Parent Control and bound it to the Master Control and Details Control (both controls have ItemId as DP).
When I select the Item from Master the details Grid is not refreshing.

How can I make sure that when I select the Item from Master User Control; the Detail User Control should show me the details?
Thanks,
Manthan