Event Driven Programming

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1 Event Driven Programming Part 3 Event Handling Chapter 12 CS 2334 University of Oklahoma Brian F. Veale 1

2 Events All interaction with a GUI program is through events Mouse clicks Button presses Text Entry Menu selection 2

3 Event Handling By default, some components appear to react to certain interaction JScrollPanes will scroll JButtons will change color when clicked In order to write functional GUI programs we must handle some events Java uses Listeners to manage event handling 3

4 Listeners When we register an object as a Listener it takes responsibility for certain events Only responsible for events from certain other components Only responsible for a limited class of events Listeners are actually interfaces They are a group of methods that we agree to implement Depending on the kind of Listener, we can have a large number of methods to implement 4

5 Common Listener Interfaces ActionListener Button being pressed Pressing return in a text field Selecting a menu item MouseListener Pressing a mouse button while over a certain component WindowListener Closing the main window KeyListener Pressing keys on the keyboard MenuListener Opening a menu Selecting a menu item More Listener Methods in the Java Tutorial Listener API Table l 5

6 Implementing Event Handling Lets make it so that our GUI programs exit when we close the window This can be annoying if not handled Without doing this, your windows disappear, but never exit This is going to be a window event connected to the JFrame We ll need to use a WindowListener WindowListener interface has 7 methods Every single one must be implemented The Adapter classes comes to our rescue, maybe You inherit from an Adapter class It contains skeletons for all corresponding Listener methods Difficulties Can only inherit from one class Not all Listeners have an Adapter Other option is to have skeleton methods for all the parts of the interface that we won t use 6

7 Exiting a Program Upon Window Closing Which method of WindowListener should we use? void windowactivated(windowevent e) Invoked when the Window is set to be the active Window. void windowclosed(windowevent e) Invoked when a window has been closed as the result of calling dispose on the window. void windowclosing(windowevent e) Invoked when the user attempts to close the window from the window's system menu. void windowdeactivated(windowevent e) Invoked when a Window is no longer the active Window. void windowdeiconified(windowevent e) Invoked when a window is changed from a minimized to a normal state. void windowiconified(windowevent e) Invoked when a window is changed from a normal to a minimized state. void windowopened(windowevent e) Invoked the first time a window is made visible. 7

8 windowclosed() or windowclosing() void windowclosed(windowevent e) Invoked when a window has been closed as the result of calling dispose on the window. void windowclosing(windowevent e) Invoked when the user attempts to close the window from the window's system menu. Window.dispose() Releases all of the native screen resources used by the Window. We will not work directly with instances of Window and therefore cannot control when dispose() is called. windowclosing() seems like the best option 8

9 Modifications to the Program frame.addwindowlistener(this); The parameter is the name of the object that will handle the event This line tells the component which object is responsible for responding to this action Class Button extends WindowAdapter or Class Button implements WindowListener The responding object must either extend the WindowAdapter Only have to implement methods we ll be using in WindowListener or implement the WindowListener interface Have to write at least a skeleton for all methods in WindowListener Write a method body for the responding object 9

10 Demo Programs that use windowclosing() ButtonWithWindowClosing.java LabeledScrollingList3.java 10

11 ActionListener Very high level event handler Can avoid some of the other types of event listeners if we use ActionListener Very common type of listener Button presses Menu item selection Has a single method public void actionperformed(actionevent e) 11

12 Handling ActionEvents We can make a single object the ActionListener for many other components Must distinguish who sent the event This data is stored in the ActionEvent object passed to actionperformed Methods for extracting event source info from ActionEvent Object getsource() Returns the object that generated the call to actionperformed String getactioncommand() Returns a string that contains the text of the object Can use setactioncommand to alter for an object Can be used for modal buttons 12

13 Other methods in ActionEvent long getwhen() Gives us the time and date the event occurred Can convert to human-readable with Date class int getmodifiers() Returns data on modifier keys pressed during event (Ctrl, Shift, etc.) String paramstring() Very useful for debugging Presents detailed information about event in textual form 13

14 ActionEvents.java ActionListener Demo 14

15 WindowAdapter In ActionEvents.java, to use a WindowAdapter to close the window, we had to create an inner class. Inner classes are a reality of life in Java GUI programs at times... But, is there a better way to close the window when the user clicks on the window close button? 15

16 public void setdefaultcloseoperation(int operation) Sets the operation that will happen by default when the user initiates a "close" on this frame. WindowConstants.DO_NOTHING_ON_CLOSE Don't do anything; require the program to handle the operation in the windowclosing method of a registered WindowListener object. WindowConstants.HIDE_ON_CLOSE Automatically hide the frame after invoking any registered WindowListener objects. Default action. WindowConstants.DISPOSE_ON_CLOSE Automatically hide and dispose the frame after invoking any registered WindowListener objects. JFrame.EXIT_ON_CLOSE Exit the application using the System exit method. Use this only in applications. 16

17 Data Models We can develop a data model for our program Abstract Data Type Our ADT can be stored in a JList Demo 1: LabeledScrollingList4.java State.java Demo 2: StateListModel.java LabeledScrollingList5.java 17

18 JList Mania The nomenclature for Swing JLists is somewhat confusing JList List Vector DefaultListModel ArrayList Keeping these classes differentiated is important 18

19 Every JList has a data view data view = data model A JList is a GUI component It shows us a view of some data The items in the list We tell the JList what data to show when we construct it JLIst mylist = new JList(Vector thedata); This view is not inherently dynamic Call the constructor as above and then try to change the vector s data Won t work too well (not at all) 19

20 Updating a JList Making a dynamic JList mylist.setlistdata(vector thenewdata); The JList will now show the current contents of the thenewdata vector Does this mean the Data model must be a Vector It could be a Vector Vector is part of the JCF Can be used as a List» We can use Collections.sort()» Can use all List methods It doesn t have to be a Vector Can use another JCF List type Just make a method that returns a Vector of your List contents 20

21 Dynamic Lists Demo DynamicStateLists.java 21

22 Clicking on a JList There are three ways to find out which item was clicked on in a JList myjlist.getselectedindex() This can work at any time Can be in ActionPerformed for a button ListSelectionListener Listener interface with only a single method public void valuechanged(listselectionevent e) Called whenever the selected item changes MouseListener Has seven methods public void mouseclicked(mouseevent e) Add this listener to JList Can detect single or double clicks Call getselectedindex() to determine which item was clicked 22

23 Beyond the JOptionPane JOptionPane was used in CS 1323 to create GUI based interfaces Very easy to use One line of code Don t necessarily need to use with Event Listeners Lack some versatility Has only a single line of input Must have a long chain of these dialogs for object input Uses Short message dialogs Actions that only need confirmation Yes/No OK/Cancel g/components/dialog.html 23

24 JDialog Swing component for Dialogs Used for modal or non-modal dialog windows Modal dialog: does not allow the user to interact with the rest of the program while dialog is active Non-Modal dialog: user can interact with program while dialog is active Construction Typically, we would write a class that inherits from JDialog JDialog mydialog = new JDialog (JFrame owner, boolean modal) The owner frame is the JFrame from which the dialog is shown Modal can be set either true or false Many other forms for the JDialog constructor 24

25 How to design and use Dialogs This is a confusing topic for many students. Controller Pattern PersonEditDialog dialog person person name etc... Person/Student/Professor 25

26 Dialog Demos SimpleDialog Demo StudentDialog.java StudentEx.java / PersonEx.java PersonEditDialog Demo PersonEditDialog.java Student.java / Professor.java / Person.java PersonEditDialog with Exception Handling PersonEditDialogEx.java StudentEx.java / ProfessorEx.java /PersonEx.java 26

CS 335 Lecture 06 Java Programming GUI and Swing

CS 335 Lecture 06 Java Programming GUI and Swing Java: Basic GUI Components Swing component overview Event handling Inner classes and anonymous inner classes Examples and various components Layouts Panels