Creating a context dependent code list for Standard UI

Hello,

I have a demand, develop the Search Help of City and County, and binding Code on the Standard View.

First, I created the BCO and the BCC of City and County;

CityBCO:

CityBCC:

CountyBCO:

CountyBCC:

Second:

I created the BO named BusinessObject1 ,created QC and OWL for this BO

Then, I opened the QC in UI designer , and binding data .

Finally，I previewed the screen QC.

I succeed in my BO.

I created the XBO named BusinessObjectExtension1 for Customer.

Then I enhanced the screen QC.

When I binding data like BO, But it is not allowed:

My Project Explorer:

I want a solution to this problem.

Thanks Very Much.