creating custom forms

A Guide to Oracle9i 1

Creating Custom Forms

Chapter 6


Lesson A Objectives

• Learn about custom forms• Create a custom form• Create command buttons that use form triggers to

manipulate data• Use the Forms Debugger to find form logic and

runtime errors• Learn how form triggers work• Create form navigation triggers


Custom Forms

• Display the data fields from a variety of database tables

• Contain programs that support organizational processes

• Not associated with one table• When creating custom forms:

– Identify the processes that the form is intended to support, then identify the associated database tables.

– Helpful to draw interface on paper


Creating a Custom Form

• Manually create the form canvas in the Object Navigator

• Create the form items by “painting” the items on the canvas, using tools on the Layout Editor tool palette

• Write the code that controls the form functions• Use a control data block

– Not associated with one database table– Contains manually drawn form items– Controlled with form triggers


System Date and Time Variables


Creating Command Buttons

• Create a command button by drawing the button on the canvas using the Button tool

• Create button triggers manually for custom forms• Trigger fires on WHEN-BUTTON-PRESSED event• If multiple buttons execute similar actions (like

clearing a form) create a separate program unit for this action


Sample Button Trigger Commands


Using the Forms Debugger to Find Runtime Errors

• Use the Forms Debugger to find runtime errors that occur while a form is running

• Identify the program line that is causing the error, and examine the variable values used within the command that has the error

• Investigate the nature of the error by looking up the error code explanation– Error codes with the FRM- prefix are Forms Builder error

codes– Error codes with the ORA- prefix are generated by the DBMS

• Look up error code on otn.oracle.com


Using the Forms Debugger

• Click the Run Form Debug button on the Forms Builder toolbar

• Set a breakpoint, which pauses execution on a specific program command

• To debug:– Examine the current values of all program variables– Step through the program commands to observe the

execution path– Examine variable values to see how the values change


Setting a Breakpoint


Forms Debug Console Windows


Viewing Text Item Values


Form Trigger Categories


Trigger Properties

• Trigger timing:– Specifies when a trigger fires– Can be just before, during, or after its triggering event– Before: PRE-– After: POST-– During: WHEN-, ON-, KEY-

• Trigger scope– Defines where an event must occur in order for trigger to fire– Includes the object to which the trigger is attached, and

contained objects


Trigger Properties

• Trigger execution hierarchy:– Defines which trigger fires when an object within a form

object contains the same trigger that the form object contains

– Can specify custom execution hierarchy


Directing Form External Navigation

• Form focus: currently selected item has form focus• External navigation:

– Occurs when the user causes the form focus to change by making a different form item active

• Internal navigation:– Occurs as a result of internal form code that responds to

external navigation operations or trigger commands

• Use external navigation to:– Specify initial form focus when form opens– Specify tab order


Setting Tab Order in Object Navigator


Directing External Navigation Using Built-in Subprograms


Lesson B Objectives

• Learn about default system messages and how to suppress them

• Create alerts and messages to provide system feedback

• Create applications that avoid user errors• Learn how to trap common runtime errors


System Message Severity Levels


Suppressing Messages

• SYSTEM.MESSAGE_LEVEL:– Variable used to suppress error messages– Set to 0, 5, 10, 15, 20, 25 to suppress all

messages with severity below this level– Default value is 0– Set value in PRE-FORM trigger


Providing System Feedback

• Custom message:– A short text string displayed on the form message

line– Use when the form needs to provide a short,

simple message that does not require an acknowledgement from the user

– To create: MESSAGE('message_string');– Can be up to 200 characters


Alerts

• Dialog box that can display a longer text message• Displays one or more buttons that allow the user to select between

alternatives that execute associated program statements• Use when:

– Message is longer than 200 characters– User acknowledgement is required– User choice is required

• See Figure 6-22 for example alert


Displaying an Alert

• In a form trigger:DECLARE

alert_button NUMBER;

BEGIN

alert_button := SHOW_ALERT('alert_name');

END;

• Use ELSIF structure to interpret and act on user response


Avoiding User Errors

• Forms should help users avoid errors by:– Validating input values– Programmatically disabling form command buttons– Disabling navigation for form text items containing

values that users should not change


Text Item Validation


Form Validation Triggers

• Item validation triggers:– Perform complex validations– Associate with WHEN-VALIDATE-ITEM event– Trigger code tests the current item value to

determine if it satisfies the validation condition– If input not valid, form displays a message and

raises a built-in exception named FORM_TRIGGER_FAILURE


Disabling Form Command Buttons

• Disable command buttons to prevent users from pressing them before form is in proper state

• SET_ITEM_PROPERTY('UPDATE_BUTTON', ENABLED, PROPERTY_FALSE);


Disabling Text Item Navigation

• Prevent users from modifying primary key values

• Make text item nonnavigable: – user cannot press the Tab key to place the

insertion point in the text item

• To prevent user clicking item:– Create a trigger that moves the insertion point to

another form item whenever the user clicks the text item using the mouse


Trapping Common Runtime Errors

• Provide better error messages for common errors• Create form-level trigger for ON-ERROR event


Syntax for ON-ERROR Trigger


Lesson C Objectives

• Convert data blocks to control blocks• Link data blocks to control blocks• Create a form that has multiple canvases• Create tab canvases• Create stacked canvases


Converting a Data Block to a Control Block

• Save time by creating a data block and converting to a control block

• To convert data block to control block:– Change the data block’s Database Data Block property

value to No– Change the Required property value of the text item that

represents the data block table’s primary key to No


Linking a Data Block to a Control Block

• Useful in complex forms with master-detail relationships

• Master is control block, details are data blocks• To link a control block with a data block:

– Create the control block– Create the data block– Specify the link between the control block and the data block– Modify the form triggers to refresh the data block when the

underlying data values change


Control/Data Block Form Example


Creating Forms with Multiple Canvases

• Use multiple screens to avoid displaying too much information

• Single-form approach: – Create one form with multiple canvases– Enables the form to share data among the different canvases– Impossible for multiple programmers to work simultaneously on

different canvases of the same application

• Multiple-form approach:– Create multiple forms with a different .fmb file for each application

canvas– Works well when multiple programmers collaborate to create a

complex application


Viewing Canvas and Block Information


Creating Multiple Canvas/Block Forms

• Specify block and canvas ordering in Object Navigator

• To navigate to another canvas programmatically, use GO_ITEM to navigate to an item on the canvas

• Refer to items in triggers with syntax :block_name.item_name

• Use caution to make sure items are placed in correct blocks


Creating and Configuring Tab Canvases in Forms

• Multiple-page canvases that allow users to move between multiple canvas surfaces by selecting tabs at the top of the canvas.

• Use to:– Display a large number of related items in a modular way– Direct a user through a sequence of steps for performing a task

• Lies on top of a content canvas within the form window.• Tab page:

– An object representing a surface that displays form items– Has a tab label identifier at the top


Creating a Tab Canvas

• To create:– Create the form– Create a new content canvas in the form– Create a tab canvas on the content canvas– Configure the tab pages


Creating a Tab Canvas


Creating and Configuring Stacked Canvases in Forms

• Lies on top of a content canvas• Use to hide canvas objects and then make the

objects appear as needed• Create by:

– Painting canvas in the desired position on an existing content canvas

– Configure stacked canvas properties– Create the form items that are to appear– Write form triggers that contain commands to display the

stacked canvas when it is needed and to hide the stacked canvas when it is not needed


Configuring a Stacked Canvas


Summary• Control blocks are created manually and do not represent

data from only one table• Control blocks can be created from data blocks to make

coding easier• Forms Debugger is used to find runtime errors in forms• User errors should be avoided by limiting opportunities for

error• User feedback is presented in message line and alert boxes• A form may contain more than one canvas; canvases can be

organized using tabs or shown and hidden programmatically

creating custom forms

Documents

form canvas

form triggersguide

form logic

form itemscontrolled

form functionsuse

different form

form object containscan

run form debug button