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"A people that
values its privileges above its principles soon loses
both." - Dwight D. Eisenhower (1890-1969), - Inaugural
Address, January 20, 1953 |
Parameter List
Introduction
With the previous versions
of Forms, the way to pass values between different forms was using
Global variables. This technique you should have already known by
previous topics in this book. Now there is a flexible way to pass
values between forms. You can create your own parameter list
programmatically and pass it as an argument in a CALL_FORM or
OPEN_FORM.
You should use the
following built-ins functions and procedures to manipulate parameter
lists:
CREATE_PARAMETER_LIST:
creates an empty parameter list.
ADD_PARAMETER: adds a
parameter to an existing parameter list.
GET_PARAMETER_LIST:
determines if there is already a parameter list with the same name as
the one you are trying to create.
DESTROY_PARAMETER_LIST:
destroys a parameter list.
DELETE_PARAMETER:
deletes a parameter in the parameter list.
Hands-on
Let’s illustrate the use
of these built-ins functions and procedures. Suppose that you need to
pass the customer ID from one form (CUSTOMERS) to another form
(PORTFOLIO); you use the CUSTOMER ID to query all customers’ stocks
portfolio in the portfolio table in the called form. You can execute
the following code from a “WHEN-BUTTON-PRESSED” trigger or even
from a menu item:
DECLARE
param_list_id ParamList; --
Define an object of type paramlist
BEGIN
param_list_id :=
GET_PARAMETER_LIST(‘my_parameter');
-- Test if the parameter
list already exists.
IF NOT
ID_NULL(param_list_id) THEN
DESTROY_PARAMETER_LIST(param_list_id);
END IF;
param_list_id :=
CREATE_PARAMETER_LIST('my_parameter');
ADD_PARAMETER(param_list_id,
'p_customer_id', TEXT_PARAMETER, :ID);
CALL_FORM('c:', NO_HIDE,
DO_REPLACE, NO_QUERY_ONLY, param_list_id);
END;
It is important to remember
that you must declare an object of type ParamList. Also, all
parameters that you define in the Object Navigator belong to the
default parameter list. You can also pass the default parameter list
to another form if you need. For example:
WHEN-BUTTON-PRESSED
BEGIN
CALL_FORM('employee',
NO_HIDE, DO_REPLACE, NO_QUERY_ONLY, 'default');
END;
When passing the default
parameter list as well as any other parameter list, make sure that
every parameter exists with the same name in the called form.
Now let us see how we can
access the value of parameter in a called form? To access the value of
a parameter in a called form, you must create the following triggers
in the employee form: WHEN-NEW-FORM-INSTANCE at the form level
In addition, create a
parameter with the same name as the parameter that you are passing in
the parameter list. If you fail to do this, the application returns an
error message that the parameter does not exist.
The following is an example
of a trigger needed to do a query based on the
value passed in the
parameter list when the form 'portfolio’ is called:
WHEN-NEW-FORM-INSTANCE
BEGIN
-- Obtain the name of the
calling form
form_name :=
GET_APPLICATION_PROPERTY(CALLING_FORM);
IF form_name IS NOT NULL
THEN
-- Execute a query if the
form is a called form
EXECUTE_QUERY;
ELSE
:parameter.p_customer_id :=
10;
END IF;
END;
Also you can create a
parameter by executing the following steps:
1) In the Object Navigator,
select the Parameters node and choose
NAVIGATOR->CREATE.
2) Bring up the properties
of the parameter and set the properties as needed.
For example, Set the
Datatype, Default Value, and Name of the parameter.
3) To access the value of
the parameter, add the reserved word PARAMETER as a prefix to the
parameter name. If you need to assign a value to a parameter, use a
regular assignment statement such as:
temp_test := :parameter.test;
-- assigns the value of the parameter to test
:parameter.test := 'value';
-- assigns a value to the parameter test
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"I'll sleep when
I'm dead." - Warren Zevon (1947-2003) |
Questions:
Q: How do you pass a
parameter from one form to another?
Q: Describe the following
build-in procedures and functions:
CREATE_PARAMETER_LIST
ADD_PARAMETER
GET_PARAMETER_LIST
DESTROY_PARAMETER_LIST
DELETE_PARAMETER
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