Using JCheckBox as CellRenderer in JComboBox

[Biliang Zhou]

Hi ranchers,

A cellRenderer question:

I have three checkBoxes: labelled Monday, Tuesday, and Wednesday, to be used to render one JComboBox. When the JComboBox is clicked, these three checkBoxes should appear in the pull down menu, and they should be allowed to be multi-selected.

I had a question on how to use JCheckBox as CellRenderer in JList before,

https://coderanch.com/t/344173/GUI/java/JCheckBox-as-CellRenderer-JList

mainly on how to make the CheckBoxes selectable in the List. This problem is solved by using a MouseListener to locate the item being checked.

Now I face a similar but different situation: use JCheckBox as CellRenderer in JComboBox. A JComboBox does not have method like

JList.locationToIndex(e.getPoint());

Thus I cannot locate which items is being checked. This confuses me...



Thanks in advance!

[Brian Cole]

I'm having trouble understanding exactly what you are trying to do. You want each item to have a checked-or-not-checked flag, but you also want combo-boxy behavior of being able to make one of the items (or a user-typed item) become the selected item?

But anyway, the popup part of the combo box is a JPopupMenu. Actually it's up to the LnF, and most or all of them use JPopupMenu, but that's what makes it a bit difficult to get your hands on it.

[Biliang Zhou]

Sorry I wasn't making myself very clear. What I want is an uneditable JComboBox with a pulldown menu populated by JCheckBoxes. These JCheckBoxes can be multi-selected.

I have figured out how to do this by searching online, and here is an adapted and quoted example:

Note: the key part is one of the methods in the class CheckComboBox: setPopupVisible(boolean flag). It must be overridden to empty, because the default setPopupVisible(boolean flag) will close the pulldown list each time you make a selection with the JCheckBoxes.

****************************************************
CAUTION: freakingly-low quality code
****************************************************

    
 
import javax.swing.*;
import java.awt.event.*;
import java.awt.*;
import java.util.HashSet;
import java.util.Iterator;
 
public class JCheckBox_Renders_JComboBox extends JFrame {
 
JPanel buttonPanel;

private static final String BLANK =       "";
private static final String DOG =         "DOG";
private static final String CAT =         "CAT";
private static final String PIG =         "PIG";
private static final String RABBIT =      "RABBIT";
private static final String OX =          "OX";
 
private static final String [] animalOption =
{BLANK, DOG, CAT, PIG, RABBIT, OX};
 
CheckComboBox checkComboBox;

JButton button;

String excludeDest;

private HashSet instructionHashset=new HashSet();
 
private JButton get_button()
{
if(button == null)
{
button = new JButton("Print");
button.addActionListener(new ActionListener(){
 
public void actionPerformed(ActionEvent arg0) {

System.out.println(getAnimals());

}});
}
return button;
}

public JCheckBox_Renders_JComboBox() {
buttonPanel = new JPanel();
 
checkComboBox = new CheckComboBox();
checkComboBox.setPreferredSize(new Dimension(120, 20));

for(int i = 0; i < animalOption.length; i ++)
{
checkComboBox.addItem(animalOption[i]);
}
buttonPanel.setLayout(new BorderLayout());
buttonPanel.add(checkComboBox, BorderLayout.CENTER);
buttonPanel.add(get_button(), BorderLayout.EAST);
 
getContentPane().add(buttonPanel,BorderLayout.NORTH);
 
setDefaultCloseOperation(EXIT_ON_CLOSE);
setSize(300, 200);
setVisible(true);
}
 
public static void main(String args[]) 
{
JCheckBox_Renders_JComboBox fe = new JCheckBox_Renders_JComboBox();
}
 
 
class CheckComboBox extends JComboBox {
CheckRenderer renderer;
 
public CheckComboBox () {
renderer = new CheckRenderer();
setRenderer(renderer);
addActionListener(this);
}
 
public void actionPerformed(ActionEvent e) {
int sel = getSelectedIndex();
 
if (sel == 0) {
getUI().setPopupVisible(this, false);
}
else if (sel > 0 && sel < (animalOption.length)) {
renderer.cbl[sel].setSelected(renderer.cbl[sel].isSelected() ? false : true);
}


}
 
/**
 * This method needs to be overriden so that the popuplist won't close
 * when user selects one opion
 */
public void setPopupVisible(boolean flag)
{
//Not code her prevents the populist from closing
}
}
 
 
class CheckRenderer extends JCheckBox implements ListCellRenderer {
public JCheckBox[] cbl = new JCheckBox[animalOption.length];
public CheckRenderer() {
setOpaque(true);
 
for(int i = 0; i < animalOption.length; i ++)
{
cbl[i] = new JCheckBox();
}
 
}
public Component getListCellRendererComponent(
JList list,
Object value,
int index,
boolean isSelected,
boolean cellHasFocus)
{
 
if (index > -1) {
cbl[index].setText(value.toString());
cbl[index].setBackground(isSelected ? Color.green : Color.white);
cbl[index].setForeground(isSelected ? Color.white : Color.black);

if(cbl[index].isSelected())
{
getInstructionHashset().add(value);
}
else
{
getInstructionHashset().remove(value);
}
return cbl[index];
}
return cbl[0];
}
}

public String getAnimals()
{
Iterator it=instructionHashset.iterator();
int i=0;
String temp="";
while(it.hasNext())
{
temp=String.valueOf(it.next());
if(i==0)
excludeDest=temp;
else
excludeDest=excludeDest+" "+temp;
i=i+1;
}
return excludeDest;
}

public HashSet getInstructionHashset() {
return instructionHashset;
}
 
}
 

****************************************************
END: freakingly-low quality code
****************************************************
[ February 26, 2007: Message edited by: Biliang Zhou ]

[Brian Cole]

I guess I still don't understand why you are using JComboBox instead of creating your own JPopupMenu from scratch.

What do you expect the JComboBox to look like when the popup is not showing?