WHEN-LIST-CHANGED Triggers Works Only Once ??

Question

hi
i have a form with the 2 list ITEMS
And i have some trigger WHEN-LIST-CHANGED For the
first LIST item which Populates the Second List
Based on the Value selected in First List
Its Works Fine For the First time.
But for second time Onward , it Does change the Value of the items in List2.
Do i have to first clear and then repopulate, i tried this but then i get a total
Blank , please help.
jai

Answer 1

From one of our support notes:
List Items populated from Record Groups are extremely useful when you need to
give your users a choice of items to choose from. This note will show you how
to create two list items that have a "master-detail" relationship, i.e., the
items appearing in the "detail" list item will depend on what is chosen in the
"master" list item.
CREATING THE LIST ITEMS
Create two list items called DEPT_LIST and ENAME_LIST. Allow them to remain
the default type of List Item, Poplists. For this situation we will not make
them base table items. Go to the property pallet of each list item, click on
the elements in list property and choose more. The cursor should be in the
very topmost item under List_Elements. Depress CTRL+SHIFT+< to remove this
default element and depress the OK button. Since you are going to populate the
list item with RG values at runtime you do not need this element. This will
avoid an "FRM-30351: No list elements defined for list item" error when
running the form.
CREATING THE RECORD GROUPS
For this example, we will use the dept and emp tables. We have a choice of
creating the Record Groups (RG) dynamically at runtime or at design
time. In this case, the easiest option is to create them at design time.
First create a RG called DEPT_GROUP with the following select statement:
SELECT TO_CHAR(DEPTNO) A,TO_CHAR(DEPTNO) B
FROM DEPT
If you are unfamiliar with the structure of the RG required when it will be
used to populate a list item please note the following:
1. A list item has both a label and a value. For this reason the select
statement brings back two fields, one which will be the label name and the other
the label value.
2. TO_CHAR is used to convert numeric values to character as the list item
contains character values.
Second, create a RG called ENAME_GROUP with the following select statement:
SELECT ENAME A, ENAME B FROM EMP ORDER BY ENAME
Note that depending upon your applications logic you may want to use the
distinct operator to prevent duplicate names. But you should be aware that
this will result in the overhead for sorting. Also, since ENAME is a VARCHAR2
data type, the to_char function is not needed.
POPULATING THE GROUPS AND LIST ITEMS
You can populate the RGs and list items from a number of triggers but the most
common is the WHEN-NEW-FORM-INSTANCE trigger. Place the following code in this
trigger:
DECLARE
V_DEPT_GROUP NUMBER;
V_ENAME_GROUP NUMBER;
BEGIN
V_DEPT_GROUP:=POPULATE_GROUP('DEPT_GROUP');
V_ENAME_GROUP:=POPULATE_GROUP('ENAME_GROUP');
POPULATE_LIST('DEPT_LIST','DEPT_GROUP');
POPULATE_LIST('ENAME_LIST','ENAME_GROUP');
END;
Note that this code is needed to initially populate both RGs and both List
Items.
If you run the form at this time you will see that DEPT_LIST contains all the
departments in Dept and ENAME_LIST contains ALL the enames in the emp table.
As our original goal was to populate ENAME_LIST depending upon what was chosen
from DEPT_LIST, we will now add the code to do this. In this situation we will
add the code to a WHEN-LIST-CHANGED trigger on DEPT_LIST. The code should
look as follows:
DECLARE
V_NUMBER NUMBER;
V_QUERY VARCHAR2(512);
BEGIN
V_QUERY:='SELECT ENAME A, ENAME B FROM EMP
WHERE DEPTNO = '||:DEPT_LIST||' ORDER BY ENAME';
V_NUMBER:=POPULATE_GROUP_WITH_QUERY('ENAME_GROUP',V_QUERY);
POPULATE_LIST('ENAME_LIST','ENAME_GROUP');
END;
First we will build a query that will contain the currently chosen department
in DEPT_LIST. This is basically the same query we created in RG ENAME_GROUP
but we are adding the where clause restriction. We then use the
populate_group_with_query built-in to repopulate the RG and then populate the
list again.
Run the form again and test. Choose department 10 from the DEPT_LIST list item
and then choose the ENAME_LIST item. You will note that the enames appearing
in ENAME_LIST will be those in department 10. This should work for any
department you choose.