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Enhanced Guide to Oracle8i

Chapter 7:Creating Custom Forms

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Data Block and Custom Forms Data block form

Based on data blocks that are associated

with specific database tables Reflect the structure of the database

Custom form

Based on control blocks that process datafrom multiple tables

Reflect business processes rather than thedatabase structure

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Creating a Custom Form1. Create the form

2. Create the form window and canvas

manually3. Create a control block

Data block that is not associated with a specifictable

Contains form items that you manually draw onthe canvas

4. Create form triggers to process data

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Form Triggers Code that is associated with a form

object and an event

Can contain SQL INSERT, UPDATE,DELETE, and SELECT commands

Referencing form text item values in

triggers:

:block_name.item_name

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Program Units Self-contained programs

Can be called from PL/SQL triggers

Used to make triggers more modular,and reuse code within triggers

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Referencing System Date and

Time Values in FormsSystem Variable Return Value

$$DATE$$ Current operating system date

$$TIME$$ Current operating system time

$$DATETIME$$ Current operating system date& time

$$DBDATE$$ Current DB server date

$$DBTIME$$ Current DB server time

$$DBDATETIME$$ Current DB server date & time

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Using the Forms Debugger

to Find Runtime Errors1. Run the form using the Run

Form Debug button2. Set a breakpoint on the program

line where you want to startexamining variable values duringexecution

Breakpoint

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Using the Forms Debugger

to Find Runtime Errors3. Run the program and execute the trigger

containing the breakpoint

4. Single-step through the code and monitor thevariable values

Execution arrow

Variablevalues

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Forms Debugger Variable

Types Module (block)

Current values of form items

Stack

Values of local variables declared inPL/SQL triggers or program units

Global Values of global variables used in

form triggers or program units

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Strategy for Using the

Forms Debugger Single-step through the trigger and

identify the program line causing the

error Run the form again and single-step

through the trigger, and note the valuesof variables just before the line

containing the error executes

Determine the cause of the error

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Form Triggers Categories

Block processing

Interface event Master-detail processing

Message handling

Navigational

Query time

Transactional

Validation

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Trigger Timing PRE-

Fires just before associated event occurs

POST-

Fires just after associated event occurs

ON-, WHEN-, KEY-

Fires immediately, in response to specificuser actions, such as key presses

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Trigger Scope Defines where an event must occur to make

the trigger fire

Trigger scope includes the object to whichthe trigger is attached, as well as all objectswithin that object Form-level: fires when event occurs within any

block or item in the form

Block-level: fires when event occurs within anyitem in the form

Item-level: fires only when event occurs withinthat item

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Trigger Execution Hierarchy If 2 related objects have the same

trigger, the higher-level objects trigger

fires first Form & block, forms trigger fires first

Block & item, blocks trigger fires first

You can specify a custom executionorder on the trigger Property Palette

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Navigational Triggers External navigation: occurs when user

causes form focus to change

Internal navigation: occurs as a resultof internal form triggers that fire inresponse to external navigation events

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User Action Triggers FiredResult on UserScreen Display

User starts formPRE-FORMPRE-BLOCK

Form appears,but with no

data visible

WHEN-NEW-FORM-INSTANCEWHEN-NEW-BLOCK-INSTANCEWHEN-NEW-RECORD-INSTANCE

WHEN-NEW-ITEM-INSTANCE

Form is

available for use

Triggers That Fire at

Form Startup

12 3

4 5

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User Action Triggers Fired Result on UserScreen Display

User places theinsertion point

in a text item

WHEN-NEW-ITEM-INSTANCEInsertion pointappears in item

WHEN-NEW-RECORD-INSTANCEWHEN-NEW-ITEM-INSTANCE

Next recordappears

User clicksthe Next Recordbutton

Triggers That Fire as a ResultOf External Navigation

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User Action Triggers FiredResult on UserScreen Display

User closesthe FormsRuntime window

Forms Runtimewindow closes

POST-BLOCKPOST-FORM

Triggers That Fire When a

Form Closes

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Directing External

Navigation Form tab order

is based on

item order inObjectNavigator block

list Formtaborder

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Moving to a Specific Form

ItemGO_ITEM(:block_name_item_name);

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Oracle Error Message Severity

Levels 5: informative message

10: informative message advising user

of procedural error 20: condition that keeps trigger from

working correctly

25 condition that keeps form fromworking correctly

>25: extreme severity

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Suppressing Lower Level

System Messages Set :SYSTEM.MESSAGE_LEVEL variable

to a higher level in PRE-FORM trigger

:SYSTEM.MESSAGE_LEVEL := 25;

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Providing User Feedback

in Forms Message

Text in message line at bottom of form

Informational only; user doesn't have torespond

Alert

Dialog box Allows user to choose different ways to proceed

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Messages

Message

Syntax:MESSAGE(message text);

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Alerts Form-level object

Object properties define alert

appearance

Title

Styleicon

Message

Buttons

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Code for Displaying an AlertDECLARE

alert_button NUMBER;

BEGIN

alert_button := SHOW_ALERT('alert_name');

IF alert_button = ALERT_BUTTON1 THEN

program statements for first button;

ELSE

program statements for second button;END IF;

END;

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Avoiding User Errors Make primary and foreign key text

items non-navigable

When user moves form focus toprimary or foreign key text item,trigger moves focus to alternate

form item

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Trapping Runtime Errors Create an ON-ERROR event trigger

Form-level trigger

Executes whenever an FRM- or ORA- erroroccurs

-FRM errors: generated by Forms

Runtime -ORA errors: generated by database

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Form Procedures That Return

System Error Information DBMS_ERROR_CODE: -ORA error code

DBMS_ERROR_TEXT: -ORA error message

ERROR_CODE: -FRM error code ERROR_TEXT: -FRM error message

MESSAGE_CODE: most recent error code

(eitherORA orFRM) MESSAGE_TEXT: most recent error message

(eitherORA orFRM)

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Structure of ON-ERROR

TriggerBEGIN--trap FRM errors

IF ERROR_CODE = FRM_error_code1 THEN

error handler;

ELSIF ERROR_CODE = FRM_error_code2 THEN

error handler;

ELSE

--trap ORA errors

IF DBMS_ERROR_CODE = -ORA_error_code1 THEN

error handler

ELSIF DBMS_ERROR_CODE = -ORA_error_code2 THEN

error handler

END IF

END IF;

END;

Code to

trapFRMerrors

Code totrap

ORAerrors

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Form Validation Ensures that form data meets preset

requirements so erroneous data is not sent todatabase

Validation unit: specifies the largest datachunk that the user can enter enter beforevalidation occurs Can be performed at the form, block, record, or

item level

Specified in the Validation Unit property on theform Property Palette

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Types of Form Validation Data

Specifies data types, lengths, and maximum and

minimum values Database

Specifies which operations a user can perform ona text item

List of Values Specifies whether a data value must be validated

against the text items LOV

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Data Blocks vs. Control Blocks Data block

Easy to create and use

Is associated with a single table, and reflects thetables structure

Control block

Requires a lot of custom programming

Can contain items from many different tables

You can link data and control blocks to takeadvantages of the strengths of each

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Linking Data Blocks and

Control Blocks1. Create the control block as the master block

2. Create the data block as the detail block, but

do not create a master-detail relationship3. Create a master-detail relationship manually in

the WHERE Clause property of the detailblock:

data_block_field := control_block.text_item

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Displaying and Refreshing the

Data Block Values Create a trigger to:

Place the insertion point in the data block

GO_BLOCK(block_name);

Flush the data block to make its dataconsistent with the master block and the

database:EXECUTE_QUERY;

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Converting a Data Block to a

Control Block Create a data block and layout that

contains most of the required text items

Convert the data block to a controlblock by changing the following blockproperties:

Database Data Block = No Required = No

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Creating a Form with Multiple

Canvases Users should be able to see all canvas

text items without scrolling

For complex applications with many textitems, divide application into multiplecanvases

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Block Navigation Order First block in Object Navigator Data

Blocks list determines block items that

first appear when form opens Users can use the Tab key to navigate

among different block items

Canvas that contains block itemsautomatically appears

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Block Navigation Order

Block order

Canvas order doesnt matter

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Controlling Block Navigation Block Navigation Style property

Same Record: navigation cycles through

items on same block Change Data Block: navigation moves to

next data block in list

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Tab Canvases Multiple-page canvases that allow users

to move among different canvas

surfaces by clicking tabs

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Tab Canvas Components Tab canvas

Collection of related tab pages

Tab pages Surfaces that display form items

Tab labels

Identifier at top of tab pageA tab canvas lies on top of a content

canvas

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Creating a Tab Canvas Use the Tab Canvas tool on the

Layout Editor tool palette to draw a tab

canvas on an existing content canvas By default, a new tab canvas has 2 tab

pages

Create new tab pages as neededAdjust tab page properties

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Important Tab Page PropertiesName: how the pageIs referenced in the form

Label: Caption thatappearson the associated tab

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Adjusting the Tab Page Order Tab page that appears first is tab page

whose block items appear first in the

Object Navigator

Block order

Tab page order

doesnt matter

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Stacked Canvases Canvas that appears on an existing

content canvas, and can be

displayed or hidden as neededAllows user to configure canvas

items

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Stacked Canvas Example

Stackedcanvas

Content

canvas

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Creating a Stacked Canvas Use the Stacked Canvas tool on the

Layout Editor tool palette to draw a

stacked canvas on an existing contentcanvas

Create block items on the stackedcanvas

Create buttons and triggers to displayand hide the stacked canvas

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Displaying and Hiding a

Stacked Canvas Displaying a stacked canvas:GO_BLOCK(stacked_canvas_block);

SHOW_VIEW(stacked_canvas);

Hiding a stacked canvas:GO_BLOCK(stacked_canvas_block);

HIDE_VIEW(stacked_canvas);