University:
California State University, Northridge
Course:
COMP 585 | Graphical User Interfaces
Academic year:

2015
Views:

89

Pages:

19
Author:

Wesley Gentry

JList, JTable, JTree Other Components With Models: JList, JTable, JTree Most GUI components maintain a state that can be modified by the user while interacting with the GUI, and which can be accessed by the underlying program. JTextField JRadioButton State: text content of the box State: boolean value indicating if button is selected or not For more complex GUI components, the state may include a significant amount of data that requires an appropriate structure to hold it. The terminology used in GUI design, taken from a study of software design patterns, is MVC or model-view-controller. Each GUI component can be ideally divided into each of these three elements: • • • Model: this element is the container or data structure that holds the data (the state) of the component View: this element is the one that appears on the GUI and shows all or a portion of the state stored in the model Controller: this element interacts with the user, responding to mouse and keystroke actions and generating events and event notifications. Java Swing has simplified the approach by treating the view and controller as a single element called a delegate (which has nothing to do with C# delegates discussed later). So Swing components follow the model-delegate architecture instead of the MVC architecture. While all components follow this architecture, it’s more significant for components that manage a large state. The most common are: • • • JList interface ListModel JTable interface TableModel JTree interface TreeModel (package javax.swing.tree) JList Component for displaying a list of objects (usually Strings). Most common construction is to start with an array of Strings, then pass this array to the JList constructor. Once the JList is instantiated, attach it to the GUI in the usual way. String[] items = { "red", "orange", "yellow", "green", "blue", "indigo", "violet" }; JList list = new JList(items); JPanel p = new JPanel(); p.add(list); Problem #1: JList has no built-in scrolling capability, so you’ll usually want to: • Add the JList to a JScrollPane • Set the number of visible rows of the JList > > String[] items = { … }; JList list = new JList(items); list.setVisibleRowCount(4); JScrollPane sp = new JScrollPane(list); JPanel p = new JPanel(); p.add(sp); Problem #2: A JList that is built in this way is static (not dynamic), its contents cannot be modified during program execution. When the JList was built, it was wrapped around a static array of strings as its model. Once the JList has been provided with such a model, it doesn’t suddenly become a dynamically expandable list without extra work. To build a dynamic list, it should use a class such as DefaultListModel as its model, which is logically similar to an ArrayList from the collections defined in the java.util package. The steps are: • • • • Create a DefaultListModel object Insert all the items into the model Create the JList Set the JList’s model to be the model we just created. To dynamically update the JList, you must add to or delete from its model, not the JList directly. Imagine an app that starts with a JList with an initial series of items. There is a text field, an “Add” button, and a “Delete” button. When the “Add” button is clicked, the content of the text field is added to the end of the JList as a new item. If the text field is empty, clicking the “Add” button does nothing. Before the item is added, the list is checked for duplicates. If the new item to be added is a duplicate of an item already in the list, a dialog box (JOptionPane) is used to get the user’s confirmation to add a duplicate item. The “Delete” button deletes the currently selected items from the list. There are three possible selection modes for a JList: • ListSelectionModel.SINGLE_SELECTION • ListSelectionModel.SINGLE_INTERVAL_SELECTION • ListSelectionModel.MULTIPLE_INTERVAL_SELECTION By default, the JList allows multiple interval selections. This means that any subset of one or more items can be selected at a time. You can change the default by using the setSelectionMode() method for the JList. After selecting the first item by clicking it, additional items are selected by clicking them while holding the CTRL key. The deletion of all selected items uses a loop that repeatedly gets the index of the first selected item, then deletes it, until there are no more selected items. Note that the index of selected items is obtained from the JList object, but items are actually deleted directly from the model, not the JList. class JListPanel extends JPanel { JList list; JTextField tf; JButton btnAdd; JButton btnDelete; String[] items = {"red","orange","yellow","green","blue","indigo", "violet"}; public JListPanel() { super(true); list = new JList(); list.setVisibleRowCount(4); DefaultListModel lm = new DefaultListModel(); for (int i=0; i v = new Vector(); for (int i=0; i

JList, JTable, JTree

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