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javaswinglayout-managergridbaglayoutjlayeredpane

JLayeredPane and GridBagConstraints


Inspired by this question JLayeredPane with a LayoutManager I'm trying to get the JLayeredPane to work with the GridBagLayout.

Here's the custom LayeredPane-class:

class StackConstraints {
    public final int layer;
    public final Object layoutConstraints;

    public StackConstraints(int layer, Object layoutConstraints) {
        this.layer = layer;
        this.layoutConstraints = layoutConstraints;
    }
}

class LXLayeredPane extends JLayeredPane {

    private static final long serialVersionUID = 1946283565823567689L;

    @Override
    protected void addImpl(Component comp, Object constraints, int index) {
        int layer = 0;
        int pos = 0;
        Object constr = null;
        if (constraints instanceof StackConstraints) {
            layer = ((StackConstraints) constraints).layer;
            constr = ((StackConstraints) constraints).layoutConstraints;
        } else {
            layer = getLayer(comp);
            constr = constraints;
        }

        pos = insertIndexForLayer(layer, index);
        super.addImpl(comp, constr, pos);
        setLayer(comp, layer, pos);
        comp.validate();
        comp.repaint();
    }
}

And here's a simple demo (similar to the standard-JLayeredPane demo but adapted for the usage of GridBagConstraints and stripped of the unnecessary stuff).

public class LayeredPaneDemo extends JPanel implements ActionListener {
    private final Color[] layerColors = { Color.yellow, Color.magenta, Color.cyan, Color.red, Color.green, Color.blue };

    private final JLayeredPane layeredPane;
    private final List<JLabel> labels;

    private JButton update;

    public LayeredPaneDemo() {
        setLayout(new BoxLayout(this, BoxLayout.PAGE_AXIS));

        labels = new ArrayList<>();

        layeredPane = new LXLayeredPane();
        layeredPane.setPreferredSize(new Dimension(400, 410));
        layeredPane.setBorder(BorderFactory.createTitledBorder("Click to change colors"));

        // Add several labels to the layered pane.
        layeredPane.setLayout(new GridBagLayout());
        for (int i = 0; i < layerColors.length; i++) {
            JLabel label = createColoredLabel("Test", layerColors[i]);
            labels.add(label);
            layeredPane.add(label, new StackConstraints(i, gbc(i)));
        }

        // Add control pane and layered pane to this JPanel.
        add(Box.createRigidArea(new Dimension(0, 10)));
        add(createControlPanel());
        add(Box.createRigidArea(new Dimension(0, 10)));
        add(layeredPane);
    }

    private GridBagConstraints gbc(int i) {
        return new GridBagConstraints(i, i, 2, 2, 0.0, 0.0, GridBagConstraints.CENTER, GridBagConstraints.BOTH,
                new Insets(0, 0, 0, 0), 0, 0);
    }

    // Create and set up a colored label.
    private JLabel createColoredLabel(String text, Color color) {
        JLabel label = new JLabel(text);
        label.setVerticalAlignment(JLabel.TOP);
        label.setHorizontalAlignment(JLabel.CENTER);
        label.setOpaque(true);
        label.setBackground(color);
        label.setForeground(Color.black);
        label.setBorder(BorderFactory.createLineBorder(Color.black));
        label.setPreferredSize(new Dimension(240, 240));
        return label;
    }

    // Create the control pane for the top of the frame.
    private JPanel createControlPanel() {
        update = new JButton("Update");
        update.addActionListener(this);
        update.setActionCommand("UPDATE");

        JPanel controls = new JPanel();
        controls.add(update);
        controls.setBorder(BorderFactory.createTitledBorder("Choose Duke's Layer and Position"));
        return controls;
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        Color prev = labels.get(labels.size() - 1).getBackground();

        for (int i = labels.size() - 1; i > 0; --i) {
            labels.get(i).setBackground(labels.get(i - 1).getBackground());
            labels.get(i).validate();
            labels.get(i).repaint();
        }
        labels.get(0).setBackground(prev);
        labels.get(0).validate();
        labels.get(0).repaint();
    }

    private static void createAndShowGUI() {
        JFrame frame = new JFrame("LayeredPaneDemo2");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JComponent newContentPane = new LayeredPaneDemo();
        newContentPane.setOpaque(true);
        frame.setContentPane(newContentPane);

        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                createAndShowGUI();
            }
        });
    }

}

My problem is that I'm adding 6 (six!) labels but only 5 (five!) are displayed. The 0-th one just vanishes somewhere. What's the reason for that?

EDIT: The initial motivation behind the pursuit is to place one (partially transparent) component on top of another like in this screenshot enter image description here The label displaying 17:00:09 has transparent background and is placed on top of the chart-component. GridBagLayout is needed to place it exactly at the top middle of the chart.


Solution

    • As @camickr has already said, JLayeredPane is irrelevant.
    • Take a look at GridBagLayout to create a board | Oracle Community. May be it helps.

      Darryl.Burke said:
      A column (or row) in a GridBagLayout is not well defined unless there is at least one component which occupies only that column (or row). All your rows have components spanning 2 columns.

    screenshot

    import java.awt.*;
    import java.awt.event.*;
    import java.util.ArrayList;
    import java.util.List;
    import javax.swing.*;
    import javax.swing.table.*;
    
    public class LayeredPaneDemo2 extends JPanel implements ActionListener {
      private final Color[] layerColors = {
          Color.yellow, Color.magenta, Color.cyan,
          Color.red, Color.green, Color.blue };
    
      private final JLayeredPane layeredPane;
      private final List<JLabel> labels;
    
      private JButton update;
    
      public LayeredPaneDemo2() {
        setLayout(new BoxLayout(this, BoxLayout.PAGE_AXIS));
    
        labels = new ArrayList<>();
        // JLayeredPane is not much related, it is a problem of how to use GridBagLayout.
        layeredPane = new LXLayeredPane();
        layeredPane.setPreferredSize(new Dimension(400, 410));
        layeredPane.setBorder(BorderFactory.createTitledBorder(
            "Click to change colors"));
    
        // Add several labels to the layered pane.
        layeredPane.setLayout(new GridBagLayout());
    
        for (int i = 0; i < layerColors.length; i++) {
          JLabel label = createColoredLabel("Test" + i, layerColors[i]);
          labels.add(label);
          layeredPane.add(label, new StackConstraints(i, gbc(i)));
        }
    //     //TEST1: Create reference grid
    //     GridBagConstraints c = new GridBagConstraints(
    //       0, 0, 1, 1, 0.0, 0.0, GridBagConstraints.CENTER,
    //       GridBagConstraints.BOTH, new Insets(0, 0, 0, 0), 0, 0);
    //     for (int i = 0; i < layerColors.length + 1; i++) {
    //       c.gridx = i;
    //       c.gridy = i;
    //       layeredPane.add(Box.createRigidArea(new Dimension(20, 20)), c);
    //     }
        //TEST2: Create reference grid >>>
        GridBagConstraints c = new GridBagConstraints(
            6, 6, 1, 1, 0.0, 0.0, GridBagConstraints.CENTER,
            GridBagConstraints.BOTH, new Insets(0, 0, 0, 0), 0, 0);
        for (int i = 0; i < layerColors.length; i++) {
          c.gridx = i;
          Component box = Box.createRigidArea(new Dimension(20, 20));
          ((JComponent) box).setBorder(BorderFactory.createLineBorder(Color.RED));
          layeredPane.add(box, c);
        }
        c.gridx = 6;
        for (int i = 0; i < layerColors.length; i++) {
          c.gridy = i;
          Component box = Box.createRigidArea(new Dimension(20, 20));
          ((JComponent) box).setBorder(BorderFactory.createLineBorder(Color.RED));
          layeredPane.add(box, c);
        }
        // <<<
        // Add control pane and layered pane to this JPanel.
        add(Box.createRigidArea(new Dimension(0, 10)));
        add(createControlPanel());
        add(Box.createRigidArea(new Dimension(0, 10)));
        add(layeredPane);
      }
    
      private GridBagConstraints gbc(int i) {
        return new GridBagConstraints(
            i, i, 2, 2, 0.0, 0.0, GridBagConstraints.CENTER,
            GridBagConstraints.BOTH, new Insets(0, 0, 0, 0), 0, 0);
      }
    
      // Create and set up a colored label.
      private JLabel createColoredLabel(String text, Color color) {
        JLabel label = new JLabel(text) {
          @Override protected void paintComponent(Graphics g) {
            g.setColor(new Color(100, 100, 100, 100));
            g.fillRect(0, 0, getWidth(), getHeight());
            super.paintComponent(g);
          }
        };
        label.setVerticalAlignment(JLabel.TOP);
        label.setHorizontalAlignment(JLabel.CENTER);
        label.setOpaque(true);
        label.setBackground(color);
        label.setForeground(Color.black);
        label.setBorder(BorderFactory.createLineBorder(Color.black));
        label.setPreferredSize(new Dimension(240, 240));
        return label;
      }
    
      // Create the control pane for the top of the frame.
      private JPanel createControlPanel() {
        update = new JButton("Update");
        update.addActionListener(this);
        update.setActionCommand("UPDATE");
    
        JPanel controls = new JPanel();
        controls.add(update);
        controls.setBorder(BorderFactory.createTitledBorder(
            "Choose Duke's Layer and Position"));
        return controls;
      }
    
      @Override
      public void actionPerformed(ActionEvent e) {
        Color prev = labels.get(labels.size() - 1).getBackground();
    
        for (int i = labels.size() - 1; i > 0; --i) {
          labels.get(i).setBackground(labels.get(i - 1).getBackground());
          labels.get(i).validate();
          labels.get(i).repaint();
        }
        labels.get(0).setBackground(prev);
        labels.get(0).validate();
        labels.get(0).repaint();
      }
    
      private static void createAndShowGUI() {
        JFrame frame = new JFrame("LayeredPaneDemo2");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    
        JComponent newContentPane = new LayeredPaneDemo2();
        newContentPane.setOpaque(true);
        frame.setContentPane(newContentPane);
    
        frame.pack();
        frame.setVisible(true);
      }
    
      public static void main(String[] args) {
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
          @Override
          public void run() {
            createAndShowGUI();
          }
        });
      }
    
    }
    
    class StackConstraints {
      public final int layer;
      public final Object layoutConstraints;
    
      public StackConstraints(int layer, Object layoutConstraints) {
        this.layer = layer;
        this.layoutConstraints = layoutConstraints;
      }
    }
    
    class LXLayeredPane extends JLayeredPane {
      @Override
      protected void addImpl(Component comp, Object constraints, int index) {
        int layer = 0;
        int pos = 0;
        Object constr = null;
        if (constraints instanceof StackConstraints) {
          layer = ((StackConstraints) constraints).layer;
          constr = ((StackConstraints) constraints).layoutConstraints;
        } else {
          layer = getLayer(comp);
          constr = constraints;
        }
    
        pos = insertIndexForLayer(layer, index);
        super.addImpl(comp, constr, pos);
        setLayer(comp, layer, pos);
        comp.validate();
        comp.repaint();
      }
    }