How to check for multiple keys at once using keyTyped(event e)-CodePudding

I have the following code:

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import javax.swing.*;
import javax.swing.event.*;

@SuppressWarnings("serial")
public class MyList extends JFrame implements ActionListener, ListSelectionListener, KeyListener
{
static MyList mylist = new MyList();

public static void main(String[] args)
{
    // TODO Auto-generated method stub
    
    JFrame frame = new JFrame();
    frame.setSize(600,800);
    frame.setDefaultCloseOperation(3);
    
    JPanel panel = new JPanel();
    
    JLabel title = new JLabel("<html><body><h1>To-Do-List</h1></body></html>");
    title.setPreferredSize(new Dimension(600, 80));
    title.setHorizontalAlignment(JLabel.CENTER);
    /*title.setOpaque(true);
    title.setBackground(Color.cyan);*/
    
    /*JTextField newTask = new JTextField();
    newTask.setHorizontalAlignment(JTextField.CENTER);
    newTask.setPreferredSize(new Dimension(400,40));*/
    JTextArea newTask_field = new JTextArea(3,1);
    newTask_field.setPreferredSize(new Dimension(400,80));
    newTask_field.setLineWrap(true);
    newTask_field.setWrapStyleWord(true);
    
    JScrollPane newTask = new JScrollPane(newTask_field);
    newTask.setPreferredSize(new Dimension(400,80));
    
    JButton confirm = new JButton("Add");
    confirm.setHorizontalAlignment(JButton.CENTER);
    confirm.setEnabled(false);
    
    DefaultListModel<String> listModel = new DefaultListModel<>();
    //listModel.addElement("");
    
    JList<String> done = new JList<String>(listModel);
    done.setPreferredSize(new Dimension(200, 400));
    
    
    DefaultListModel<String> listModel2 = new DefaultListModel<>();
    
    JList<String> notDoneYet = new JList<String>(listModel2);
    notDoneYet.setPreferredSize(new Dimension(200, 400));
    
    panel.add(title);
    //panel.add(newTask);
    panel.add(newTask);
    panel.add(mylist.createEmptySpace(new JLabel(), 600, 40));
    panel.add(confirm);
    panel.add(mylist.createEmptySpace(new JLabel(), 600, 0));
    panel.add(done);
    panel.add(mylist.createEmptySpace(new JLabel(), 100, 400));
    panel.add(notDoneYet);
    frame.add(panel);
    frame.setVisible(true);
    
    
    //-------------------------------//
    
    newTask.setFocusable(true);
    newTask_field.setFocusable(true);
    
    if(newTask_field.getText().equals(""))
    {
        //unused if-statement
    }
    newTask.addKeyListener(new KeyListener()
    {
        
        @Override
        public void keyTyped(KeyEvent e) {
            // TODO Auto-generated method stub
            if(e.getKeyCode()==KeyEvent.VK_A)
            {
                
            }
            
        }
        
        @Override
        public void keyReleased(KeyEvent e) {
            // TODO Auto-generated method stub
            
        }
        
        @Override
        public void keyPressed(KeyEvent e) {
            // TODO Auto-generated method stub
            
        }
    });
    
    
}

//Method createEmptySpace(JLabel(), int, int) which works.
}

Now I want it to run the keyTyped event everytime I press a key which prints a character (a-z, 1-9, 0, special signs like *, , # and so on). (Also, I would like to check if the JTextArea is empty after I pressed Enter, Backspace or Delete). The problem is, doing a regular if-else or switch-case-statement is ridiculous. Imagine doing 26 10 dontKnowHowMuch conditions to check every single key like this. Is there a way to make it short so I don't need to stretch it like that?

Update: I wrote the following code into the KeyListener:

newTask_field.addKeyListener(new KeyListener()
    {
        
        @Override
        public void keyTyped(KeyEvent e) {
            // TODO Auto-generated method stub
            if(e.getKeyCode()==KeyEvent.VK_A)
            {
                confirm.setEnabled(true);
                newTask_field.setText(newTask_field.getText()   e.getKeyCode());
            }
            if(e.getKeyCode()==KeyEvent.VK_ALPHANUMERIC)
            {
                System.out.println("Alphanumeric sign");
                confirm.setEnabled(true);
                newTask_field.setText(newTask_field.getText()   e.getKeyChar());
            }
            if(e.getKeyChar()==KeyEvent.VK_UNDEFINED)
            {
                System.out.println("Undefined");
            }
            
        }
        
        @Override
        public void keyReleased(KeyEvent e) {
            // TODO Auto-generated method stub
            
            
            
            if(e.getKeyCode()==KeyEvent.VK_BACK_SPACE || e.getKeyCode()==KeyEvent.VK_DELETE
                    || e.getKeyCode()==KeyEvent.VK_ENTER || e.getKeyCode()==KeyEvent.VK_SPACE
                    || e.getKeyCode()==KeyEvent.VK_TAB || e.getKeyCode()==KeyEvent.VK_CIRCUMFLEX
                    || e.getKeyCode()==KeyEvent.VK_DEAD_ACUTE || e.getKeyCode()==KeyEvent.VK_DEAD_GRAVE)
            {
                if (newTask_field.getText().isBlank())
                {
                    confirm.setEnabled(false);
                }
            }
            
            if(e.getKeyCode()==KeyEvent.VK_UNDEFINED)
            {
                System.out.println("Undefined");
            }
        }
        
        @Override
        public void keyPressed(KeyEvent e) {
            // TODO Auto-generated method stub
            
        }
    });

And no matter what I typed in the JTextArea and no matter whether the KeyListener is for newTask or for newTask_field, nothing ever happens. The signs appear in the JTextArea, but the KeyListener does nothing. Any ideas why?

CodePudding user response：

Quickly taking a look at https://docs.oracle.com/javase/7/docs/api/java/awt/event/KeyEvent.html reveals the 'getKeyChar()'-Method(https://docs.oracle.com/javase/7/docs/api/java/awt/event/KeyEvent.html#getKeyChar()), which returns the character of the pressed key.

So you can then use:

newTask_field.setText(newTas_field.getText()   e.getKeyChar());

As for Enter, Backspace and Delete, there you just check, if you pressed those and do your actions.

So therefore your keyTyped-Body could/should look like this:

if ((e.getKeyCode() == KeyEvent.ENTER || e.getKeyCode() == KeyEvent.BACK_SPACE || e.getKeyCode() == KeyEvent.DELETE) && newTask_field.getText().Equals("")) {
    //do your stuff
    return;
}
newTask_field.setText(newTas_field.getText()   e.getKeyChar());

Hope this solves your problem.

Edit:

After testing the code myself a bit i found the problem, that you add the listener to newTask. After i added the listener to newTask_field instad of newTask, it worked fine.

Out of scope: Maybe create a separate Main-class for the main-Method and have the MyList as a class without a main-Method. Then you create all the objects in the constructor and move on from there.

CodePudding user response：

From the info you've provided, it seems that you need something like the PropertyChangeListener().

newTask_field.addPropertyChangeListener(new PropertyChangeListener() {
            
            @Override
            public void propertyChange(PropertyChangeEvent evt) {
                if(evt.getNewValue().equals("")) {
                
                    confirm.setEnabled(false);
                }else {
                    confirm.setEnabled(true);
                }
            }
        });

UPDATE:

Or, turns out in order to manipulate the text property changes in Swing JTextField you need to use addDocumentListener()

newTask_field.getDocument().addDocumentListener(new DocumentListener() {
            
            @Override
            public void removeUpdate(DocumentEvent e) {
                if(txt.getText().equals("")) {
                    confirm.setEnabled(false);
                }
                
            }
            
            @Override
            public void insertUpdate(DocumentEvent e) {
                confirm.setEnabled(true);
                
            }
            
            @Override
            public void changedUpdate(DocumentEvent e) {
                confirm.setEnabled(true);
                
            }
        });