Transcript Creating Custom Forms - Oracle9i

Creating Custom Forms
Chapter 6
A Guide to Oracle9i
1
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
A Guide to Oracle9i
2
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
A Guide to Oracle9i
3
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
A Guide to Oracle9i
4
System Date and Time Variables
A Guide to Oracle9i
5
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
A Guide to Oracle9i
6
Sample Button Trigger Commands
A Guide to Oracle9i
7
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
A Guide to Oracle9i
8
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
A Guide to Oracle9i
9
Setting a Breakpoint
A Guide to Oracle9i
10
Forms Debug Console Windows
A Guide to Oracle9i
11
Viewing Text Item Values
A Guide to Oracle9i
12
Form Trigger Categories
A Guide to Oracle9i
13
Trigger Properties
• Trigger timing:
–
–
–
–
–
Specifies when a trigger fires
Can be just before, during, or after its triggering event
Before: PREAfter: POSTDuring: 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
A Guide to Oracle9i
14
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
A Guide to Oracle9i
15
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
A Guide to Oracle9i
16
Setting Tab Order in Object Navigator
A Guide to Oracle9i
17
Directing External Navigation Using
Built-in Subprograms
A Guide to Oracle9i
18
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
A Guide to Oracle9i
19
System Message Severity Levels
A Guide to Oracle9i
20
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
A Guide to Oracle9i
21
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
A Guide to Oracle9i
22
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
A Guide to Oracle9i
23
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
A Guide to Oracle9i
24
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
A Guide to Oracle9i
25
Text Item Validation
A Guide to Oracle9i
26
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
A Guide to Oracle9i
27
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);
A Guide to Oracle9i
28
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
A Guide to Oracle9i
29
Trapping Common Runtime Errors
• Provide better error messages for common errors
• Create form-level trigger for ON-ERROR event
A Guide to Oracle9i
30
Syntax for ON-ERROR Trigger
A Guide to Oracle9i
31
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
A Guide to Oracle9i
32
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
A Guide to Oracle9i
33
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
A Guide to Oracle9i
34
Control/Data Block Form Example
A Guide to Oracle9i
35
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
A Guide to Oracle9i
36
Viewing Canvas and Block
Information
A Guide to Oracle9i
37
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
A Guide to Oracle9i
38
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
A Guide to Oracle9i
39
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
A Guide to Oracle9i
40
Creating a Tab Canvas
A Guide to Oracle9i
41
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
A Guide to Oracle9i
42
Configuring a Stacked Canvas
A Guide to Oracle9i
43
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
A Guide to Oracle9i
44