Creating Custom Forms

1
Creating Custom Forms

• Chapter 6

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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

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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

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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

5
System Date and Time Variables
6
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

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Sample Button Trigger Commands
8
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

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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

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Setting a Breakpoint
11
Forms Debug Console Windows
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Viewing Text Item Values
13
Form Trigger Categories
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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

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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

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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

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Setting Tab Order in Object Navigator
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Directing External Navigation Using Built-in
Subprograms
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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

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System Message Severity Levels
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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

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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

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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

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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

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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

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Text Item Validation
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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

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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)

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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

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Trapping Common Runtime Errors

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

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Syntax for ON-ERROR Trigger
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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

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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 blocks Database Data Block
  property value to No
• Change the Required property value of the text
  item that represents the data block tables
  primary key to No

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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

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Control/Data Block Form Example
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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

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Viewing Canvas and Block Information
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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

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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

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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

41
Creating a Tab Canvas
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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

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Configuring a Stacked Canvas
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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