Creating and Using Dialogs

1
Creating and Using Dialogs

• A dialog is a box that pops up and prompts the
  user for a value or informs them of something
• One way directly create objects of type JDialog

Object
Component
Container
Window
Dialog
JDialog
2
Using JDialog

• JDialog, like JFrame, JWindow, and JApplet, uses
  a content pane to organize its contents
• If you create a JDialog directly, you are
  responsible for
• Laying out the dialog components (BorderLayout by
  default)
• Messages and Icons
• Input areas and Buttons (Yes, No, Ok, Cancel,
  etc.)
• Adding listeners to the dialog components
• Showing and hiding the dialog when appropriate

3
Another Way JOptionPane

• The JOptionPane class has a number of static
  methods that do the work of creating, laying out,
  and adding listeners for dialogs that perform
  standard functions
• The methods are of the form showXXXDialog where
  XXX is
• Message Tell the user about something that has
  happened
• Confirm Ask a confirming question, like
  yes/no/cancel
• Input Prompt for some input
• Option Combination of the above

4
General Dialog Layout
Message
Icon
Input Value
Option Buttons

• Note the dialogs created by the JOptionPane
  class are modal, that is, processing is blocked
  until user interaction is complete

5
An Example Dialog Task

• Put up a dialog that
• Displays an icon indicating this is a dialog that
  is transmitting information
• Displays the message ''A CATASTROPHIC ERROR HAS
  OCCURRED''
• Displays a single button labeled ''OK''
• Adds a listener to the button that causes the
  dialog to disappear when the button is clicked,
  allowing processing to continue

6
A Simple Message Dialog
import javax.swing. public class DialogTest
public static void main(String args)
JOptionPane.showMessageDialog(
null, "A CATASTROPHIC ERROR HAS
OCCURRED.") System.exit(0)
7
Notes On The Example

• As a static method, showMessageDialog must be
  fully qualified by the class name
• As a void method, showMessageDialog is called for
  side effect
• The first argument is the dialog's parent
  component. If null, the dialog is centered on
  the screen
• The second argument is an Object to be displayed,
  often a String
• Output

8
Dialogs That Ask Questions

• The showConfirmDialog method can present more
  than one button, from among Yes, No, OK, and
  Cancel
• A symbolic integer is returned indicating which
  button was clicked
• JOptionPane.CANCEL_OPTION
• JOptionPane.YES_OPTION
• JOptionPane.NO_OPTION
• JOptionPane.OK_OPTION
• Use this value to determine the course of action
  to take after interaction with the user

9
showConfirmDialog Example
... int response
JOptionPane.showConfirmDialog(
null, "DO YOU WANT TO
CONTINUE?") if (response
JOptionPane.YES_OPTION) ... // user
clicked YES else if (response
JOptionPane.NO_OPTION) ... //
user clicked NO else
... // user clicked CANCEL
...
10
Changing the Dialog Title and Buttons

• All showXXXDialog methods have multiple versions
  allowing different combinations of arguments
• Suppose you want only the OK and Cancel buttons,
  and a non-default dialog title

11
Changing the Dialog Title and Buttons (cont'd)
... int response JOptionPane.showConfirmDia
log( null, "DO YOU WANT TO
CONTINUE?", "Continue Dialog", // Dialog
title JOptionPane.OK_CANCEL_OPTION) if
(response JOptionPane.OK_OPTION) ... //
user clicked OK else ... // user clicked
CANCEL
12
Getting Textual Input

• showInputDialog can return a string that is input
  by the user
• There are many argument combinations. Here is
  the simplest

... String ssn JOptionPane.showInputDialog(
"ENTER YOUR SOCIAL SECURITY NUMBER") ...
13
Getting List Selections
Suppose you want a dialog to present the user
with a list of possible selections
When the user clicks on the input area, a
drop-down list appears
14
Getting List Selections (cont'd)
This requires a 7-argument call to
showInputDialog
... String message "Select your
favorite cereal" String title "Cereal
Selection" Object selectionValues
"Corn Flakes", "Wheaties",
"Cheerios" Object response
JOptionPane.showInputDialog(
null, message,
title, JOptionPane.QUESTION_MES
SAGE, // message type null,
// icon
selectionValues, // selections
selectionValues0) //
initially
// selected String favoriteCereal
(String)response ...