CODEWITHSUNDEEP
javaswingjframekeylistener
user4189129
user4189129

Reputation:

Making a keyevent in a JFrame

I'm trying to make a key make something happen in a JFrame. Right now I'm just trying to disable a button when you press the left key, but nothing is happening. I thought I have everything right, but it does nothing.

EDIT: I noticed that when I don't click start first, it works. But after you press start, it won't respond.

Here's my code so far:

import java.awt.*;
import java.awt.event.*;

import javax.swing.*;



public class MyFrame extends JFrame implements ActionListener, KeyListener
{
private static final long serialVersionUID = 1L;
private JPanel p1;
private JButton b1, b2;
private JLabel lb1;
private int a;
private Font font = new Font("Arial", Font.BOLD, 20);


public MyFrame()
{
    setLayout(new FlowLayout());
    setSize(700,600);
    setVisible(true);
    setResizable(false);
    addKeyListener(this);
    setFocusable(true);

    p1 = new JPanel(); add(p1);
    p1.setBackground(Color.BLACK);
    p1.setPreferredSize(new Dimension(650,500));
    p1.setFocusable(true);
    b1 = new JButton("Start"); add(b1);
    b1.addActionListener(this);
    b2 = new JButton("Test"); add(b2);
    b2.setFocusable(true);

    setDefaultCloseOperation(EXIT_ON_CLOSE);
}

public void actionPerformed(ActionEvent event)
{
    Graphics g = p1.getGraphics();
    g.setColor(Color.WHITE);
    g.fillRect(30, 210, 10, 70);
    g.fillRect(620, 210, 10, 70);
    for(int i=0; i<7; i++)
    {
        g.fillRect(325, a, 10, 70);
        a += 90;
    }
    g.setFont(font);
    g.drawString("Player 1: ", 120, 20);
    g.drawString("Player 2: ", 450, 20);
}

public void keyPressed(KeyEvent e) 
{
    int d = e.getKeyCode();
    if(d==KeyEvent.VK_LEFT)
    {
        b2.setEnabled(false);
    }
}

public void keyReleased(KeyEvent e) 
{


}

public void keyTyped(KeyEvent e) 
{


}

}

And here's my Main.java file:

public class Main { 
public static void main(String[] arg)
{
    MyFrame mf = new MyFrame();
}

}

Upvotes: 1

Views: 136

Answers (2)

Paul Samsotha
Paul Samsotha

Reputation: 208964

KeyListener has a lot of problems, with regards to focus (among other things). With Swing, it is preferred to use Key Bindings, which gives us more control over the focus options. There are different InputMaps for WHEN_FOCUSED, WHEN_ANCESTOR_OF_FOCUSED_COMPONENT, WHEN_IN_FOCUSED_WINDOW. Their names are almost self documenting. So if we were to do 

JPanel panel = (JPanel)frame.getContentPane();
InputMap imap = panel.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW);

then we are getting the InputMap for when the frame is focused. We would then bind a KeyStroke with an Action to that InputMap and the component's ActionMap. For example

JPanel panel = (JPanel)frame.getContentPane();
InputMap imap = panel.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW);
imap.put(KeyStroke.getKeyStroke("LEFT"), "leftAction");
ActionMap amap = panel.getActionMap();
Action leftAction = new AbstractAction() {
    @Override
    public void actionPerformed(ActionEvent e) {
        doSomethingWhenLeftIsPressed();
    }
};
amap.put("leftAction", leftAction);

Resources

Upvotes: 3

Iootu
Iootu

Reputation: 344

You forgot to tell the JFrame that it should be listening for keys with this line of code:addKeyListener(this);

Upvotes: 1

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