Is it possible to use KeyBindings in JFrame & Canv

Question

I've been have difficulty with KeyListener (not detecting keys) and I'm trying to switch over to KeyBindings but JFrame doesn't extend JComponent which is needed for the getInputMap() function. Any ideas?

Answer 1

Use a surrogate JComponent instead. For example, set the frame's contentPane to be a JPanel and use it to register the key bindings.

This is a very basic example, which uses a JPanel as the contentPane and adds a Canvas to it. The key bindings are then registered through the JPanel on behalf of the Canvas which is actually used to respond to them.

import java.awt.BorderLayout;
import java.awt.Canvas;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;
import javax.swing.AbstractAction;
import javax.swing.Action;
import javax.swing.ActionMap;
import javax.swing.InputMap;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.KeyStroke;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Test {

    public static void main(String[] args) {
        new Test();
    }

    public Test() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setContentPane(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        private Surface surface;

        public TestPane() {
            setLayout(new BorderLayout());

            surface = new Surface();

            InputMap inputMap = getInputMap(WHEN_IN_FOCUSED_WINDOW);
            ActionMap actionMap = getActionMap();

            inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_A, 0, false), "Pressed.left");
            inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_A, 0, true), "Release.left");
            inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_D, 0, false), "Pressed.right");
            inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_D, 0, true), "Release.right");
            inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_W, 0, false), "Pressed.up");
            inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_W, 0, true), "Release.up");
            inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_S, 0, false), "Pressed.down");
            inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_S, 0, true), "Release.down");

            actionMap.put("Pressed.left", surface.getLeftPressAction());
            actionMap.put("Release.left", surface.getLeftReleaseAction());
            actionMap.put("Pressed.right", surface.getRightPressAction());
            actionMap.put("Release.right", surface.getRightReleaseAction());
            actionMap.put("Pressed.up", surface.getUpPressAction());
            actionMap.put("Release.up", surface.getUpReleaseAction());
            actionMap.put("Pressed.down", surface.getDownPressAction());
            actionMap.put("Release.down", surface.getDownReleaseAction());

            add(surface);
        }

    }

    public class Surface extends Canvas {

        private String displayText = "...";

        @Override
        public void paint(Graphics g) {
            super.paint(g); 
            Graphics2D g2d = (Graphics2D) g.create();
            FontMetrics fm = g2d.getFontMetrics();
            int x = (getWidth() - fm.stringWidth(displayText)) / 2;
            int y = ((getHeight() - fm.getHeight()) / 2) + fm.getAscent();
            g2d.drawString(displayText, x, y);
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }

        public Action getLeftPressAction() {
            return new TextAction("Left");
        }

        public Action getLeftReleaseAction() {
            return new ClearAction();
        }

        public Action getRightPressAction() {
            return new TextAction("Right");
        }

        public Action getRightReleaseAction() {
            return new ClearAction();
        }

        public Action getUpPressAction() {
            return new TextAction("Up");
        }

        public Action getUpReleaseAction() {
            return new ClearAction();
        }

        public Action getDownPressAction() {
            return new TextAction("Down");
        }

        public Action getDownReleaseAction() {
            return new ClearAction();
        }

        public class TextAction extends AbstractAction {
            private String text;

            public TextAction(String text) {
                this.text = text;
            }

            @Override
            public void actionPerformed(ActionEvent e) {
                displayText = text;
                repaint();
            }

        }

        public class ClearAction extends AbstractAction {

            @Override
            public void actionPerformed(ActionEvent e) {
                displayText = "...";
                repaint();
            }

        }

    }

}

This example only override's the Canvass paint method, but the concept should still work for implementations using BufferStrategy