Extra-length combo-box popup sizing and positioning in multi-screen environment

FlatScreenInfo

Scale factors:  125% / 150%
Java version:   11.0.7

ID:      \Display0 (main)
Size:    1920 x 1080 / 32 Bit / 60 Hz
Bounds:  1536 x 864 / x 0 / y 0   (scale -1.25)
Insets:  left 0 / right 0 / top 0 / bottom 50
Scale:   1.25

ID:      \Display1
Size:    1920 x 1080 / 32 Bit / 60 Hz
Bounds:  1280 x 720 / x -1280 / y -50   (scale -1.5)
Insets:  left 0 / right 0 / top 0 / bottom 0
Scale:   1.5

Using the following sample program:

//package ;

import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.Container;
import java.awt.GraphicsConfiguration;
import java.awt.Point;
import java.awt.geom.AffineTransform;
import java.util.LinkedHashSet;
import java.util.Set;

import javax.swing.BorderFactory;
import javax.swing.Box;
import javax.swing.JComboBox;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.LookAndFeel;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.plaf.metal.MetalLookAndFeel;
import javax.swing.plaf.metal.MetalTheme;

@SuppressWarnings("serial")
public class ComboBoxTest extends JFrame {

    private Container mainPane;
    private JLabel scaleLabel;

    public ComboBoxTest() {
        super("Combo-box test");
        add(initMainPanel(), BorderLayout.CENTER);
        add(initStatusBar(), BorderLayout.PAGE_END);
    }

    private Container initMainPanel() {
        JComboBox<String> history = new JComboBox<>();
        history.addItem(randomItem(50));
        history.addItem(randomItem(500));
        history.addItem(randomItem(100));

        JComponent main = new JPanel(new BorderLayout());
        main.setBorder(BorderFactory.createEmptyBorder(10, 10, 10, 10));
        main.add(history, BorderLayout.PAGE_START);
        mainPane = main;
        return main;
    }

    private static String randomItem(int maxLength) {
        StringBuilder buf = new StringBuilder(maxLength + 10);
        buf.append(randomWord());
        while (buf.length() < maxLength) {
            buf.append(' ').append(randomWord());
        }
        return buf.toString();
    }

    private static String randomWord() {
        final int length = (int) (Math.random() * 5 + 5);
        StringBuilder buf = new StringBuilder(length);
        for (int i = 0; i < length; i++) {
            buf.append((char) (Math.random() * 26 + 'a'));
        }
        return buf.toString();
    }

    private Component initStatusBar() {
        LookAndFeel lnf = UIManager.getLookAndFeel();
        String lnfLabel = "Look and Feel: " + lnf.getName();
        if (lnf instanceof MetalLookAndFeel) {
            lnfLabel += " / " + MetalLookAndFeel.getCurrentTheme().getName();
        }

        scaleLabel = new JLabel();
        updateScaleLabel();
        addPropertyChangeListener("graphicsConfiguration", evt -> updateScaleLabel());

        JComponent status = Box.createHorizontalBox();
        status.add(new JLabel(lnfLabel));
        status.add(new JLabel(", "));
        status.add(scaleLabel);
        status.add(Box.createHorizontalGlue());
        return status;
    }

    void updateScaleLabel() {
        GraphicsConfiguration gc = getGraphicsConfiguration();
        if (gc == null) {
            scaleLabel.setText("Scale: ?");
        } else {
            AffineTransform defaultTransform = gc.getDefaultTransform();
            Set<Double> factors = new LinkedHashSet<>(1);
            factors.add(defaultTransform.getScaleX());
            factors.add(defaultTransform.getScaleY());
            scaleLabel.setText("Scale: " + factors);
        }
    }

    public static void main(String[] args) throws Exception {
        SwingUtilities.invokeLater(() -> {
            setLookAndFeel(args.length > 0 ? args[0] : null);

            ComboBoxTest frame = new ComboBoxTest();
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.pack();
            frame.setSize(frame.getFont().getSize() * 50, frame.getHeight());
            frame.setLocation(new Point(0, 0));
            frame.mainPane.requestFocusInWindow();
            frame.setVisible(true);
        });
    }

    static void setLookAndFeel(String param) {
        if (param == null)
            return;

        String lnfClassName, themeClassName;
        switch (param.toLowerCase()) {
        case "ocean":
            lnfClassName = "javax.swing.plaf.metal.MetalLookAndFeel";
            themeClassName = "javax.swing.plaf.metal.OceanTheme";
            break;
        case "steel":
            lnfClassName = "javax.swing.plaf.metal.MetalLookAndFeel";
            themeClassName = "javax.swing.plaf.metal.DefaultMetalTheme";
            break;
        case "nimbus":
            lnfClassName = "javax.swing.plaf.nimbus.NimbusLookAndFeel";
            themeClassName = null;
            break;
        case "flatlaf":
            lnfClassName = "com.formdev.flatlaf.FlatLightLaf";
            themeClassName = null;
            break;
        case "plastic":
            lnfClassName = "com.jgoodies.looks.plastic.Plastic3DLookAndFeel";
            themeClassName = "com.jgoodies.looks.plastic.theme.SkyBluer";
            break;
        case "system":
            lnfClassName = UIManager.getSystemLookAndFeelClassName();
            themeClassName = null;
            break;
        case "default":
            lnfClassName = UIManager.getCrossPlatformLookAndFeelClassName();
            themeClassName = null;
            break;
        default:
            return;
        }

        try {
            if (themeClassName != null) {
                MetalLookAndFeel.setCurrentTheme((MetalTheme) Class
                        .forName(themeClassName).getConstructor().newInstance());
            }
            UIManager.setLookAndFeel(lnfClassName);
        } catch (LinkageError | ReflectiveOperationException | UnsupportedLookAndFeelException e) {
            e.printStackTrace();
        }
    }

}

java -cp flatlaf-0.42.jar ComboBoxTest.java flatlaf

Moving the application window to the left (secondary) monitor, then opening the combo-box popup – the popup is misaligned, using the resolution/scaling of the right (main) monitor and extends across the right monitor end:

In my opinion, the popup should not extend across monitors.

Not sure if it is related, I’m noticing – without the extra-length item:

        history.addItem(randomItem(50));
        history.addItem(randomItem(75));
        history.addItem(randomItem(100));

when moving the application window between monitors (<kbd>Win+Shift+Left/Right-Arrow</kbd>), the first time the combo popup is opened it is shown at a weird position:

The second time the popup is opened it is aligned/positioned as expected.

[DevCharly]

If the taskbar/dock is at the bottom, Swing changes the location of combobox popup so that the popup never overlaps the taskbar/dock. So I think it should also not overlap the taskbar/dock if it is on the right or left side.

[stanio]

Thank you. I saw the change and wondered if screen insets should be considered (as is currently) for a popup. Maybe it is o.k. as the insets might be occupied by an always-on-top window which might show even on top of the popup.