问题
Hi hope someone can tell me what I am doing wrong with my Key Event.
I am using a Card Layout to navigate through two of my JPanels atm. To do so I use Action Events as well as Key Events. The action events will toggle between JPanels when a button is pressed while the key events will hide away the buttons when a key is pressed. All good with the key events, it does what I want (call a method on one of the panels to set the bounds of the buttons placed inside it eq: button.setBounds(-1, -1, 150, 40); but when I press any of the buttons the key event wont respond despite not having any event on the buttons that I press. Below is my code, for simplicity I removed the non relevant parts of the panels like what they are meant to do.
Thanks in advance and please let me know if I need to provide more clues or to edit the code more, I will try my best to make the code clearer.
public class PanelContainer extends JPanel implements ActionListener, KeyListener{
GamePanel game = new GamePanel();
MainMenuPanel mainMenu = new MainMenuPanel();
CardLayout cards = new CardLayout();
public PanelContainer(){
setLayout(cards);
this.setFocusable(true);
this.addKeyListener(this);
mainMenu.newGameButton.addActionListener(this);
add(mainMenu, "Card1");
add(game, "Card2");
}
@Override
public void actionPerformed(ActionEvent aevt){
cards.show(this, "Card2");
game.action();
}
@Override
public void keyTyped(KeyEvent kevt){
}
@Override
public void keyPressed(KeyEvent kevt){
}
@Override
public void keyReleased(KeyEvent kevt){
if(kevt.getKeyCode() == KeyEvent.VK_ESCAPE || kevt.getKeyChar() == 'O' || kevt.getKeyChar() == 'o'){
game.shw(); //shw() is a method inside GamePanel that sets the bounds of the buttons
}
else if (kevt.getKeyChar() == 'h' || kevt.getKeyChar() == 'H'){game.hid();}
}
}
public class MainMenuPanel extends JPanel
{
private URL workingDir = this.getClass().getResource("imgresources/brick_wall.png") ;
private ImageIcon icon = new ImageIcon(workingDir) ;
private Image img = icon.getImage();
//create and initiate buttons;
JButton newGameButton = new JButton("New Game");
JButton highScoreButton = new JButton("High Scores");
JButton controlsButton = new JButton("Controls");
Point[] points = new Point[1000];
public MainMenuPanel(){
add(newGameButton);
add(highScoreButton);
add(controlsButton);
setPoints();
}
public void setButtonsBounds(){
newGameButton.setBounds(450, 200, 200, 40);
highScoreButton.setBounds(450, 250, 200, 40);
controlsButton.setBounds(450, 300, 200, 40);
}
@Override
public void paintComponent(Graphics g){
try{
super.paintComponent(g);
Graphics2D d2 = (Graphics2D) g;
d2.setColor(new Color(0, 0, 0));
d2.fillRect(0, 0, this.getWidth(), this.getHeight());
setButtonsBounds();
for(int i=0; i<275; i++){
d2.drawImage(img, points[i].x +200, points[i].y, this);
}
}catch(Exception e){}
}
}
public class GamePanel extends JPanel implements Runnable{
JButton button = new JButton("Main Menu");
JButton button2 = new JButton("Exit Game");
void shw(){
add(button);
add(button2);
button.setBounds(400, 200, 150, 20);
button2.setBounds(400, 240, 150, 20);
}
void hid(){
button.setBounds(1, 1, 150, 20);
button2.setBounds(1, 40, 150, 20);
}
}
回答1:
It's a focus issue. Use Key Bindings instead of a KeyListener so you don't have to worry about this issue (and for other benefits as well -- check the Key Bindings tutorial for details).
Here's my SSCCE that demonstrates what I'm talking about. Note that both KeyListener and key bindings work until you press a button, and then only bindings work:
import java.awt.event.*;
import javax.swing.*;
public class KeyBindingsEg {
private static void createAndShowGui() {
PanelContainer mainPanel = new PanelContainer();
JFrame frame = new JFrame("KeyBindingsEg");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(mainPanel);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}
@SuppressWarnings("serial")
class PanelContainer extends JPanel {
public PanelContainer() {
this.setFocusable(true);
this.addKeyListener(new MyKeyListener());
JButton newGameButton = new JButton("New Game");
newGameButton.addActionListener(new MyActionListener());
add(newGameButton);
setKeyBindings();
}
private void setKeyBindings() {
Action hideAction = new BindingAction(BindingAction.HIDE);
Action showAction = new BindingAction(BindingAction.SHOW);
int condition = JComponent.WHEN_IN_FOCUSED_WINDOW;
InputMap inputMap = getInputMap(condition);
ActionMap actionMap = getActionMap();
actionMap.put(BindingAction.HIDE, hideAction);
inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_H, 0), BindingAction.HIDE);
inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_H, KeyEvent.SHIFT_DOWN_MASK),
BindingAction.HIDE);
int[] showKeys = { KeyEvent.VK_O, KeyEvent.VK_ESCAPE };
actionMap.put(BindingAction.SHOW, showAction);
for (int key : showKeys) {
inputMap.put(KeyStroke.getKeyStroke(key, 0), BindingAction.SHOW);
inputMap.put(KeyStroke.getKeyStroke(key, KeyEvent.SHIFT_DOWN_MASK),
BindingAction.SHOW);
}
}
private class MyActionListener implements ActionListener {
@Override
public void actionPerformed(ActionEvent aevt) {
System.out.println("button pressed");
}
}
private class MyKeyListener extends KeyAdapter {
public void keyReleased(KeyEvent kevt) {
if (kevt.getKeyCode() == KeyEvent.VK_ESCAPE
|| kevt.getKeyChar() == 'O' || kevt.getKeyChar() == 'o') {
System.out.println("KeyListener: show");
} else if (kevt.getKeyChar() == 'h' || kevt.getKeyChar() == 'H') {
System.out.println("KeyListener: hide");
}
}
}
private class BindingAction extends AbstractAction {
public static final String HIDE = "Hide";
public static final String SHOW = "Show";
public BindingAction(String text) {
super(text);
putValue(ACTION_COMMAND_KEY, text);
}
@Override
public void actionPerformed(ActionEvent evt) {
String actionCommand = evt.getActionCommand();
if (actionCommand.equals(HIDE)) {
System.out.println("key bindings: hide");
} else if (actionCommand.equals(SHOW)) {
System.out.println("key bindings: show");
}
}
}
}
来源：https://stackoverflow.com/questions/9150034/java-key-event-wont-execute-once-i-press-a-button