how do you add a key listener to a java GUI?
can anyone pls show me how...
or at least give an example..pls:)
cause I want to add a key listener to my GUI calculator
but I don't now how or where to put it and stuff...:-/
thanks...
talablink
0
Newbie Poster
Recommended Answers
Jump to PostSun's tutorial is a good palce to start.
Tutorial: Writing a Key Listener
If you still have unanswered questions after that, just post them here :)
Jump to PostWhy does your listener need to extend JPanel? Your class can just implement KeyListener or extend KeyAdapter and be added to a component with the .addKeyListener( new MyListener() ) call. When a key is pressed in that component, the listener will fire and you process it accordingly.
All 5 Replies
Ezzaral
2,714
Posting Sage
Team Colleague
Featured Poster
Sun's tutorial is a good palce to start.
Tutorial: Writing a Key Listener
If you still have unanswered questions after that, just post them here :)
talablink
0
Newbie Poster
my key listener is on the last part...and i don't know what to do with it...
i'm suppose to add a key listener to this code...
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
import java.awt.event.KeyListener;
import java.awt.event.KeyEvent;
class CalcGUI extends JPanel {
//=============================================== instance variables
//--- variable for GUI elements
private JTextField _displayField; // display result / input.
//--- variables representing state of the calculator
private boolean _startNumber = true; // true: num key next
private double _resultValue = 0.0; // result so far
private String _previousOp = "="; // previous operation
//end instance variables
//-------------------------------------------- static (class) variables
private static final Font BIGGER_FONT = new Font("monspaced",
Font.PLAIN, 24);
//======================================================constructor
public CalcGUI() {
//--- Display field
_displayField = new JTextField("0", 12);
_displayField.setHorizontalAlignment(JTextField.RIGHT);
_displayField.setFont(BIGGER_FONT);
//--- Clear button
JButton clearButton = new JButton("CLEAR");
clearButton.setFont(BIGGER_FONT);
clearButton.addActionListener(
new ActionListener() {
public void actionPerformed(ActionEvent e) {
action_clear();
}
}
);
//--- Use one listener for all numeric keys.
ActionListener numListener =
new ActionListener() {
public void actionPerformed(ActionEvent e) {
action_num(e); // process it below
}
};
//--- Layout numeric keys in a grid.
//--- Use the characters in a string as a guide
//--- for producing the numeric keys.
String buttonOrder = "789456123 0 ";
JPanel buttonPanel = new JPanel(new GridLayout(5, 3));
for (int i = 0; i < buttonOrder.length(); i++) {
String keyTop = buttonOrder.substring(i, i+1);
if (keyTop.equals(" ")) {
buttonPanel.add(new JLabel(""));
} else {
JButton b = new JButton(keyTop);
b.addActionListener(numListener);
b.setFont(BIGGER_FONT);
buttonPanel.add(b);
}
}
//--- Create an ActionListener that will be used for
//--- all of the operator buttons.
ActionListener opListener =
new ActionListener() {
public void actionPerformed(ActionEvent e) {
action_op(e);
}//endmethod actionPerformed
};
//--- Create panel with gridlayout to hold operator buttons.
//--- Use array of button names to create buttons in a loop.
JPanel opPanel = new JPanel(new GridLayout(5, 1));
String[] opOrder = {"+", "-", "*", "/", "=","%"};
for (int i = 0; i < opOrder.length; i++) {
JButton b = new JButton(opOrder[i]);
b.addActionListener(opListener);
b.setFont(BIGGER_FONT);
opPanel.add(b);
}
JButton c= new JButton(".");
c.setFont(BIGGER_FONT);
opPanel.add(c);
/**c.addKeyListener( new KeyListener (){
public void keyPressed( KeyEvent e){
_displayField.setText(".");
}
});*/
//--- Layout this, the top level, panel.
this.setLayout(new BorderLayout());
this.add(_displayField, BorderLayout.NORTH );
this.add(buttonPanel , BorderLayout.CENTER);
this.add(opPanel , BorderLayout.EAST );
this.add(clearButton , BorderLayout.SOUTH );
this.add(MyPanel, BorderLayout.SOUTH);
}//end constructor
//============================================================ action_op
// Called by the action listener for all op buttons.
private void action_op(ActionEvent e) {
// The calculator is always in one of two states.
// 1. A number must be entered next (so this operator is wrong).
// 2. An operator must be entered next (so we're ok).
if (_startNumber) { // Error: needed number, not operator
action_clear();
_displayField.setText("ERROR");
} else {
_startNumber = true; // Next thing must be a number
try {
// Get the value from display field, convert it, do prev op
// If this is the first op, _previousOp will be =.
int currentValue =
Integer.parseInt(_displayField.getText());
double currentValuez = Double.parseDouble(_displayField.getText());
//int d=Integer.parseInt(c);
if (_previousOp.equals("=")) {
_resultValue = currentValue;
} else if (_previousOp.equals("+")) {
_resultValue += currentValuez;
} else if (_previousOp.equals("-")) {
_resultValue -= currentValuez;
} else if (_previousOp.equals("*")) {
_resultValue *= currentValuez;
} else if (_previousOp.equals("/")) {
_resultValue /= currentValue;
} else if (_previousOp.equals("%")) {
_resultValue %= currentValue;
}
_displayField.setText(""+_resultValue);
} catch (NumberFormatException ex) {
action_clear();
_displayField.setText("Error");
}
//--- set _previousOp for the next operator.
_previousOp = e.getActionCommand();
}//endif _startNumber
}//endmethod action_op
//======================================================== action_num
// Called by the action listener for numeric keys
private void action_num(ActionEvent e) {
String digit = e.getActionCommand(); // gets text from digitkey
if (_startNumber) {
// This is the first digit, clear field and set
_displayField.setText(digit);
_startNumber = false;
} else {
// Add this digit to the end of the display field
_displayField.setText(_displayField.getText() + digit);
}
}//endmethod action_num
//=============================================== logic action_clear
// Called by the action listener for the Clear button
public void action_clear() {
_startNumber = true;
_displayField.setText("0");
_resultValue = 0.0;
_previousOp = "=";
}//endmethod action_clear
}//endclass CalcGUI
class MyPanel extends JPanel implements KeyListener{
public MyPanel(){
this.setFocusable(true);
this.addKeyListener(this);
}
public void keyTyped(KeyEvent e){
char i = e.getKeyChar();
System.out.println("Key Typed: " + i);
}
public void keyPressed(KeyEvent e){
char i = e.getKeyChar();
System.out.println("Key Pressed: " + i);
}
public void keyReleased(KeyEvent e){
char i = e.getKeyChar();
System.out.println("Key Released: " + i);
}
}
Ezzaral
2,714
Posting Sage
Team Colleague
Featured Poster
Why does your listener need to extend JPanel? Your class can just implement KeyListener or extend KeyAdapter and be added to a component with the .addKeyListener( new MyListener() ) call. When a key is pressed in that component, the listener will fire and you process it accordingly.
phamvantu_ctk30
0
Newbie Poster
Đầu tiên cho Focus cái JPanel rùi cho nó lắng nghe KeyListener trên chínhd nó là OK.
this.setFocusable(true);
this.addKeyListener((KeyListener)this);
package AppKeyListener;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
public class MyPanel extends JPanel implements KeyListener {
public MyPanel(){
super();
this.setBackground(Color.gray);
this.setFocusable(true);
this.addKeyListener((KeyListener)this);
}
@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor(color);
g.fillRect(x, y, 100, 50);
}
int x=100,y=50;
Color color=Color.red;
// Main method
public static void main(String[] args) {
// TODO code application logic here
JFrame frm =new JFrame("App Key Listener");
frm.setSize(400, 300);
frm.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frm.setVisible(true);
MyPanel p =new MyPanel();
frm.add(p);
}
public void keyTyped(KeyEvent e) {
//throw new UnsupportedOperationException("Not supported yet.");
}
public void keyPressed(KeyEvent e) {
if(e.getKeyChar()=='g')
color=Color.GREEN;
if(e.getKeyChar()=='r')
color=Color.red;
if(e.getKeyChar()=='b')
color=Color.blue;
if(e.getKeyChar()=='y')
color=Color.yellow;
if(e.getKeyChar()=='w')
color=Color.WHITE;
if(e.getKeyCode()==KeyEvent.VK_UP)
y-=2;
if(e.getKeyCode()==KeyEvent.VK_DOWN)
y+=2;
if(e.getKeyCode()==KeyEvent.VK_RIGHT)
x+=2;
if(e.getKeyCode()==KeyEvent.VK_LEFT)
x-=2;
this.repaint();
}
public void keyReleased(KeyEvent e) {
//throw new UnsupportedOperationException("Not supported yet.");
}
}
phamvantu_ctk30
0
Newbie Poster
Add KeyListener on Jpanel:
Focus JPanel and add KeyListener on its. OK.hjhj
this.setFocusable(true);
this.addKeyListener((KeyListener)this);
package AppKeyListener;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
public class MyPanel extends JPanel implements KeyListener {
public MyPanel(){
super();
this.setBackground(Color.gray);
this.setFocusable(true);
this.addKeyListener((KeyListener)this);
}
@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor(color);
g.fillRect(x, y, 100, 50);
}
int x=100,y=50;
Color color=Color.red;
// Main method
public static void main(String[] args) {
// TODO code application logic here
JFrame frm =new JFrame("App Key Listener");
frm.setSize(400, 300);
frm.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frm.setVisible(true);
MyPanel p =new MyPanel();
frm.add(p);
}
public void keyTyped(KeyEvent e) {
//throw new UnsupportedOperationException("Not supported yet.");
}
public void keyPressed(KeyEvent e) {
if(e.getKeyChar()=='g')
color=Color.GREEN;
if(e.getKeyChar()=='r')
color=Color.red;
if(e.getKeyChar()=='b')
color=Color.blue;
if(e.getKeyChar()=='y')
color=Color.yellow;
if(e.getKeyChar()=='w')
color=Color.WHITE;
if(e.getKeyCode()==KeyEvent.VK_UP)
y-=2;
if(e.getKeyCode()==KeyEvent.VK_DOWN)
y+=2;
if(e.getKeyCode()==KeyEvent.VK_RIGHT)
x+=2;
if(e.getKeyCode()==KeyEvent.VK_LEFT)
x-=2;
this.repaint();
}
public void keyReleased(KeyEvent e) {
//throw new UnsupportedOperationException("Not supported yet.");
}
}
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