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JComboBox determines if items are / are not displayed in a drop-down list

I tried to determine for all elements if they are visible or not visible in JViewPort from the JComboBox drop-down list

(my friday ot)

EDIT: I don't want to use MouseListener to repeat events for System.out.print (...)

it is not possible to pass a JComboBox with a JList declared by JCombo # Model using SwingUtilities http://download.oracle.com/javase/6/docs/api/javax/swing/SwingUtilities.html , but this APi came out of my ...

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class ItemVisibleRecCombo extends JFrame {

    private static final long serialVersionUID = 1L;
    private JComboBox fontsBox;

    public ItemVisibleRecCombo() {
        String[] numbers = {"one", "two", "three", "four", "five", "six", "seven"};
        fontsBox = new JComboBox(numbers);
        fontsBox.setSelectedItem(0);
        fontsBox.addItemListener(new ItemListener() {

            @Override
            public void itemStateChanged(ItemEvent e) {
                if (e.getStateChange() == ItemEvent.SELECTED) {
                    manItemInCombo();
                }
            }
        });
        fontsBox.setModel(new DefaultComboBoxModel(numbers));
        fontsBox.setMaximumRowCount(3);
        add(fontsBox, BorderLayout.CENTER);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setPreferredSize(new Dimension(400, 60));
        setLocation(200, 105);
        pack();
        setVisible(true);
    }

    private void manItemInCombo() {
        if (fontsBox.getItemCount() > 0) {
            final Object comp = fontsBox.getUI().getAccessibleChild(fontsBox, 0);
            if ((comp instanceof JPopupMenu)) {
                final JList list = new JList(fontsBox.getModel());
                final JPopupMenu popup = (JPopupMenu) comp;
                final JScrollPane scrollPane = (JScrollPane) popup.getComponent(0);
                final JViewport viewport = scrollPane.getViewport();
                final Rectangle rect = popup.getVisibleRect();
                Point pt = viewport.getViewPosition();
                for (int i = 0; i < list.getModel().getSize(); i++) {
                    pt = list.indexToLocation(i);
                    System.out.print(pt + " - ");
                    rect.setLocation(rect.x - pt.x, rect.y - pt.y);
                    System.out.println(new Rectangle(viewport.getExtentSize()).contains(rect));
                }
            }
        }
    }

    public static void main(String arg[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                ItemVisibleRecCombo ivrc = new ItemVisibleRecCombo();
            }
        });
    }
}
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4 answers

Basically, you are looking for list.locationToIndex (if I understood correctly), something like

    Accessible a = fontsBox.getUI().getAccessibleChild(fontsBox, 0);
    if (a instanceof javax.swing.plaf.basic.ComboPopup) {
        JList list = ((javax.swing.plaf.basic.ComboPopup)a).getList();
        Rectangle rect = list.getVisibleRect();
        int first = list.locationToIndex(rect.getLocation());
        // similar for last, at the lower edge of the visible rect, left as exercise <g>
        // Edit: as of @Boro comment, last is easier calculated with maxRowCount
        int last = first + fontsBox.getMaximumRowCount() - 1;
        ....

, , :

   list.getVisibleRowCount() == combo.getMaximumRowCount()

: /, , , ; -)

+3

, combobox, ,

                Point pt = viewport.getViewPosition();
                int rowCount = fontsBox.getMaximumRowCount();
                int rowsize = viewport.getSize().height / rowCount;
                System.out.println("viewport.getHeight()="+ viewport.getHeight()
                        +"; viewport.getViewSize().getHeight()="+ viewport.getViewSize().getHeight()
                        +"; rowsize=" + rowsize+"; pt="+pt);                
                int firstVisibleElementIndex = pt.y/rowsize;
                int lastVisibleElementIndex = firstVisibleElementIndex + (rowCount-1);
                System.out.println("firstVisibleElementIndex="+ firstVisibleElementIndex
                        +"; lastVisibleElementIndex="+lastVisibleElementIndex);

, , , .

: (& ) , . . @kleopatra.

+2

ItemListener ActionListener, , , , :

fontsBox.addActionListener(new ActionListener() {

    @Override
    public void actionPerformed(ActionEvent e) {
         manItemInCombo();
    }
});
+1

, , , , ViewPort , , phaaaa

EDIT @Anthony Accioly sugestion Changing the listener from ItemListener to ActionListener

ItemListener

1stIndex = 0, LastIndex = 2, SelectedItem1 = two, Value = one, two, three//ok
1stIndex = 0, LastIndex = 2, SelectedItem1 = three, Value = one, two, three//ok
1stIndex = 0, LastIndex = 2, SelectedItem1 = four, Value = one, two, three//wrong
1stIndex = 1, LastIndex = 3, SelectedItem1 = five, Value = two, three, four//wrong
1stIndex = 2, LastIndex = 4, SelectedItem1 = six, Value = three, four, five//wrong
1stIndex = 3, LastIndex = 5, SelectedItem1 = seven, Value = four, five, six//wrong
1stIndex = 4, LastIndex = 6, SelectedItem1 = six, Value = five, six, seven//ok
1stIndex = 4, LastIndex = 6, SelectedItem1 = five, Value = five, six, seven//ok
1stIndex = 4, LastIndex = 6, SelectedItem1 = four, Value = five, six, seven//wrong
1stIndex = 3, LastIndex = 5, SelectedItem1 = three, Value = four, five, six//wrong
1stIndex = 2, LastIndex = 4, SelectedItem1 = two, Value = three, four, five//wrong
1stIndex = 1, LastIndex = 3, SelectedItem1 = one, Value = two, three, four//wrong

ActionListener

1stIndex = 0, LastIndex = 2, SelectedItem1 = two, Value = one, two, three
1stIndex = 0, LastIndex = 2, SelectedItem1 = three, Value = one, two, three
1stIndex = 1, LastIndex = 3, SelectedItem1 = four, Value = two, three, four
1stIndex = 2, LastIndex = 4, SelectedItem1 = five, Value = three, four, five
1stIndex = 3, LastIndex = 5, SelectedItem1 = six, Value = four, five, six
1stIndex = 4, LastIndex = 6, SelectedItem1 = seven, Value = five, six, seven
1stIndex = 4, LastIndex = 6, SelectedItem1 = six, Value = five, six, seven
1stIndex = 4, LastIndex = 6, SelectedItem1 = five, Value = five, six, seven
1stIndex = 3, LastIndex = 5, SelectedItem1 = four, Value = four, five, six
1stIndex = 2, LastIndex = 4, SelectedItem1 = three, Value = three, four, five
1stIndex = 1, LastIndex = 3, SelectedItem1 = two, Value = two, three, four
1stIndex = 0, LastIndex = 2, SelectedItem1 = one, Value = one, two, three


import java.awt.*;
import java.awt.event.*;
import javax.accessibility.Accessible;
import javax.swing.*;

public class ItemVisibleRecCombo extends JFrame {

    private static final long serialVersionUID = 1L;
    private JComboBox fontsBox;

    public ItemVisibleRecCombo() {
        String[] numbers = {"one", "two", "three", "four", "five", "six", "seven"};
        fontsBox = new JComboBox(numbers);
        fontsBox.setSelectedItem(0);
        /*fontsBox.addItemListener(new ItemListener() {

        @Override
        public void itemStateChanged(ItemEvent e) {
        if (e.getStateChange() == ItemEvent.SELECTED) {
        manItemInCombo();
        }
        }
        });*/
        fontsBox.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                manItemInCombo();
            }
        });
        fontsBox.setModel(new DefaultComboBoxModel(numbers));
        fontsBox.setMaximumRowCount(3);
        add(fontsBox, BorderLayout.CENTER);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setPreferredSize(new Dimension(400, 60));
        setLocation(200, 105);
        pack();
        setVisible(true);
    }

    private void manItemInCombo() {
        if (fontsBox.getItemCount() > 0) {
            final Accessible a = fontsBox.getUI().getAccessibleChild(fontsBox, 0);
            if (a instanceof javax.swing.plaf.basic.ComboPopup) {
                final JList list = ((javax.swing.plaf.basic.ComboPopup) a).getList();
                final Rectangle rect = list.getVisibleRect();
                final int first = list.locationToIndex(rect.getLocation());
                final int last = first + fontsBox.getMaximumRowCount() - 1;
                String selectedItem = fontsBox.getSelectedItem().toString();
                System.out.println("1stIndex = " + first + ", LastIndex = "
                        + last + ", SelectedItem1 = " + selectedItem
                        + ", Value = " + fontsBox.getItemAt(first).toString()
                        + ", " + fontsBox.getItemAt(first + 1).toString()
                        + ", " + fontsBox.getItemAt(first + 2).toString());
            }
        }
    }

    public static void main(String arg[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                ItemVisibleRecCombo ivrc = new ItemVisibleRecCombo();
            }
        });
    }
}
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