12advanced Swing

1 © 2001-2003 Marty Hall, Larry Brown http://www.corewebprogramming.com
core
programming
Advanced Swing
Custom Data Models and Cell Renderers

Advanced Swing2 www.corewebprogramming.com
Agenda
• Building a simple static JList
• Adding and removing entries from
a JList at runtime
• Making a custom data model
– Telling JList how to extract data from
existing objects
• Making a custom cell renderer
– Telling JList what GUI component to use for
each of the data cells

MVC Architecture
• Custom data models
– Changing the way the GUI control obtains the data.
Instead of copying data from an existing object into a
GUI control, simply tell the GUI control how to get at the
existing data.
• Custom cell renderers
– Changing the way the GUI control displays data values.
Instead of changing the data values, simply tell the GUI
control how to build a Swing component that represents
each data value.
• Main applicable components
– JList
– JTable
– JTree

JList with Fixed Set of Choices
• Build JList: pass strings to constructor
– The simplest way to use a JList is to supply an array of
strings to the JList constructor. Cannot add or remove
elements once the JList is created.
String options =
{ "Option 1", ... , "Option N"};
JList optionList = new JList(options);
• Set visible rows
– Call setVisibleRowCount and drop JList into JScrollPane
optionList.setVisibleRowCount(4);
JScrollPane optionPane =
new JScrollPane(optionList);
someContainer.add(optionPane);
• Handle events
– Attach ListSelectionListener and use valueChanged

Simple JList: Example Code
public class JListSimpleExample extends JFrame {
...
public JListSimpleExample() {
super("Creating a Simple JList");
WindowUtilities.setNativeLookAndFeel();
addWindowListener(new ExitListener());
Container content = getContentPane();
String[] entries = { "Entry 1", "Entry 2", "Entry 3",
"Entry 4", "Entry 5", "Entry 6"};
sampleJList = new JList(entries);
sampleJList.setVisibleRowCount(4);
sampleJList.addListSelectionListener
(new ValueReporter());
JScrollPane listPane = new JScrollPane(sampleJList);
...
}

Simple JList: Example Code
(Continued)
private class ValueReporter implements ListSelectionListener {
/** You get three events in many cases -- one for the
* deselection of the originally selected entry, one
* indicating the selection is moving, and one for the
* selection of the new entry. In the first two cases,
* getValueIsAdjusting returns true; thus, the test
* below since only the third case is of interest.
*/
public void valueChanged(ListSelectionEvent event) {
if (!event.getValueIsAdjusting()) {
Object value = sampleJList.getSelectedValue();
if (value != null) {
valueField.setText(value.toString());
}
}
}
}
}

Simple JList: Example Output

JList with Changeable Choices
• Build JList:
– Create a DefaultListModel, add data, pass to constructor
String choices = { "Choice 1", ... , "Choice N"};
DefaultListModel sampleModel = new DefaultListModel();
for(int i=0; i<choices.length; i++) {
sampleModel.addElement(choices[i]);
}
JList optionList = new JList(sampleModel);
• Set visible rows
– Same: Use setVisibleRowCount and a JScrollPane
• Handle events
– Same: attach ListSelectionListener and use valueChanged
• Add/remove elements
– Use the model, not the JList directly

Changeable JList:
Example Code
String[] entries = { "Entry 1", "Entry 2", "Entry 3",
"Entry 4", "Entry 5", "Entry 6"};
sampleModel = new DefaultListModel();
for(int i=0; i<entries.length; i++) {
sampleModel.addElement(entries[i]);
}
sampleJList = new JList(sampleModel);
sampleJList.setVisibleRowCount(4);
Font displayFont = new Font("Serif", Font.BOLD, 18);
sampleJList.setFont(displayFont);
JScrollPane listPane = new JScrollPane(sampleJList);

Changeable JList:
Example Code (Continued)
private class ItemAdder implements ActionListener {
/** Add an entry to the ListModel whenever the user
* presses the button. Note that since the new entries
* may be wider than the old ones (e.g., "Entry 10" vs.
* "Entry 9"), you need to rerun the layout manager.
* You need to do this <I>before</I> trying to scroll
* to make the index visible.
*/
public void actionPerformed(ActionEvent event) {
int index = sampleModel.getSize();
sampleModel.addElement("Entry " + (index+1));
((JComponent)getContentPane()).revalidate();
sampleJList.setSelectedIndex(index);
sampleJList.ensureIndexIsVisible(index);
}
}
}

Changeable JList:
Example Output

JList with Custom Data Model
• Build JList
– Have existing data implement ListModel interface
• getElementAt
– Given an index, returns data element
• getSize
– Tells JList how many entries are in list
• addListDataListener
– Lets user add listeners that should be notified
when an item is selected or deselected.
• removeListDataListener
– Pass model to JList constructor
• Set visible rows & handle events: as before
• Add/remove items: use the model

Custom Model: Example Code
public class JavaLocationListModel implements ListModel {
private JavaLocationCollection collection;
public JavaLocationListModel
(JavaLocationCollection collection) {
this.collection = collection;
}
public Object getElementAt(int index) {
return(collection.getLocations()[index]);
}
public int getSize() {
return(collection.getLocations().length);
}
public void addListDataListener(ListDataListener l) {}
public void removeListDataListener(ListDataListener l) {}
}

Actual Data
public class JavaLocationCollection {
private static JavaLocation[] defaultLocations =
{ new JavaLocation("Belgium",
"near Liege",
"flags/belgium.gif"),
new JavaLocation("Brazil",
"near Salvador",
"flags/brazil.gif"),
new JavaLocation("Colombia",
"near Bogota",
"flags/colombia.gif"),
... }; ...
}
• JavaLocation has toString plus 3 fields
– Country, comment, flag file

JList with Custom Model:
Example Code
JavaLocationCollection collection =
new JavaLocationCollection();
JavaLocationListModel listModel =
new JavaLocationListModel(collection);
JList sampleJList = new JList(listModel);
Font displayFont =
new Font("Serif", Font.BOLD, 18);
sampleJList.setFont(displayFont);
content.add(sampleJList);

JList with Custom Model:
Example Output

JList with Custom Cell
Renderer
• Idea
– Instead of predetermining how the JList will draw the list
elements, Swing lets you specify what graphical
component to use for the various entries.
Attach a ListCellRenderer that has a
getListCellRendererComponent method that determines
the GUI component used for each cell.
• Arguments to
getListCellRendererComponent
– JList: the list itself
– Object: the value of the current cell
– int: the index of the current cell
– boolean: is the current cell selected?
– boolean: does the current cell have focus?

Custom Renderer:
Example Code
public class JavaLocationRenderer extends
DefaultListCellRenderer {
private Hashtable iconTable = new Hashtable();
public Component getListCellRendererComponent
(JList list, Object value, int index,
boolean isSelected, boolean hasFocus) {
JLabel label = (JLabel)super.getListCellRendererComponent
(list,value,index,isSelected,hasFocus);
if (value instanceof JavaLocation) {
JavaLocation location = (JavaLocation)value;
ImageIcon icon = (ImageIcon)iconTable.get(value);
if (icon == null) {
icon = new ImageIcon(location.getFlagFile());
iconTable.put(value, icon);
}
label.setIcon(icon);
...
return(label);
}}

Custom Renderer:
Example Output

Summary
• Simple static JList
– Pass array of strings to JList constructor
• Simple changeable JList
– Pass DefaultListModel to JList constructor. Add/remove
data to/from the model, not the JList.
• Custom data model
– Have real data implement ListModel interface.
– Pass real data to JList constructor.
• Custom cell renderer
– Assign a ListCellRenderer
– ListCellRenderer has a method that determines the
Component to be used for each cell

12advanced Swing

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12advanced Swing