Keyboard input in JPanel

Question

I have a problem with listening to keyboard input in JPanel. I tried almost everything! Please help me with this one. I will be very grateful.

Here is my code:

public class SudokuBoardDisplay extends JPanel implements Printer, KeyListener{

private static final long serialVersionUID = 1L;
    private Dimension size = new Dimension(500,100);
    private SudokuBoard game;
    private List<JButton> fields = new ArrayList<JButton>();
    private int clickedX = -1;
    private int clickedY = -1;
    private int userValue = -1;

public SudokuBoardDisplay(SudokuBoard board) {
    this.game = board;

    this.setLayout(new GridBagLayout());

    JButton picLabel;

    for(int i=0; i<SudokuBoard.TAB_SIZE*SudokuBoard.TAB_SIZE; i++){
        picLabel = new JButton();
        picLabel.setPreferredSize(new Dimension(50,50));
        picLabel.setFont(new Font("Serif", Font.PLAIN, 40));
        picLabel.setBorder(BorderFactory.createDashedBorder(getForeground()));
        picLabel.setActionCommand(Integer.toString(i));
        fields.add(picLabel);
    }

    for(JButton button : fields){
        button.addActionListener(new ActionListener(){
            public void actionPerformed(ActionEvent e) {
                for(int y=0; y<SudokuBoard.TAB_SIZE; y++){
                    for(int x=0; x<SudokuBoard.TAB_SIZE; x++){
                        if(e.getActionCommand().equals(Integer.toString(x+y*SudokuBoard.TAB_SIZE))){
                            clickedX=x;
                            clickedY=y;
                            draw();
                            revalidate();
                            repaint();
                        }
                    }
                }
            }
        });
    }


    this.addKeyListener(this);
    this.setFocusable(true);
    this.requestFocusInWindow();

    draw();

    this.setVisible(true);
}

public void keyPressed(KeyEvent e) {
    int userValue = Character.getNumericValue(e.getKeyChar());
    System.out.println(userValue);
    //((SudokuBoardDisplay)(printer)).setUserValue(userValue);
    //this.requestFocusInWindow();
}

public void keyReleased(KeyEvent e) {

}

public void keyTyped(KeyEvent e) {

}

}

public class MainWindow extends JFrame{

public MainWindow(){
    this.setLayout(new FlowLayout());

    btnSolve = new JButton("Solve");
    printer = new SudokuBoardDisplay(game);
    dao = DaoFactory.createDao("WorkingDirectory/SAVE");
    dao.write(game);

    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setSize(600,650);
    setResizable(false);

    btnSolve.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent arg0) {
            SudokuSolver solver = new BacktrackingSudokuSolver();
            try {
                game = solver.solve(game);
            } catch (SolutionHasBeenFound e) {
            }
            printer.show(game);

        }
    });
    add(btnSolve);


    btnSave = new JButton("Save");
    btnSave.addActionListener(new ActionListener(){

        public void actionPerformed(ActionEvent arg0) {
             dao.write(game);
        }

    });
    add(btnSave);

    btnLoad = new JButton("Load");
    btnLoad.addActionListener(new ActionListener(){

        public void actionPerformed(ActionEvent arg0) {
             game = (SudokuBoard) dao.read();
             printer.show(game);
        }

    });
    add(btnLoad);

    btnNew = new JButton("New");

    btnNew.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent arg0) {
            game = new SudokuBoard(5);
            printer.show(game);
        }

    });


    add(btnNew);

    add((JPanel) printer);

    setVisible(true);
}

}

I've deleted irrelevant pieces of code.

The focus always is on "solve" button even if I try to request focus on the JPanel.

Answer 1

Call ((JPanel) printer).requestFocus();

after setVisible(true);

For more info have a look at JComponent#requestFocus()

Answer 2

Consider using Key Bindings instead, they provide more control over the focus level requirements need in order to generate key events, unlike KeyListener which must be registered to a component that both is focusable and has focus in order for it to raise key events