KeyListener problem

[Veronique Kus]

Hi,
I'm actually able to get this ode to work but I just don't understand why one way works and the other doesn't - would appreciate it if someone could explain it to me...
So I've got a class that represents a tab in a tabbed pane (MapTab), this tab contains an instance of the DrawingCanvas class for drawing shapes. First, in the MapTab class, I register the drawingCanvas object to listen to mouse events (the DrawingCanvas class implements the MouseListener & MouseMotionListener interfaces. This works fine:

package mywordmaps;

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.util.ArrayList;
import java.util.Iterator;
import javax.swing.*;

public class MapTab extends Tab {
	private DrawingCanvas drawingCanvas;

	public MapTab(JTabbedPane tabbedPane, String title) {
		super(tabbedPane, title);	
		this.setLayout(new GridLayout());
		addDrawingCanvas();	
	}
	
	private void addDrawingCanvas() {
            drawingCanvas = new DrawingCanvas();
	    addMouseListener(drawingCanvas);
	    addMouseMotionListener(drawingCanvas);
	    add(drawingCanvas);
	    drawingCanvas.setOpaque(true);
	    drawingCanvas.setVisible(true);
	}
	
	...
	
	class DrawingCanvas extends JPanel implements MouseListener, MouseMotionListener {
		...
	   
		public DrawingCanvas() {
			...
		}
		
		...
		
		// Mouse events handling
		public void mouseClicked(MouseEvent e) {
			..
		}
		public void mouseEntered(MouseEvent e){}
		public void mouseExited(MouseEvent e){}
		public void mousePressed(MouseEvent e) {
		}
		
		public void mouseReleased(MouseEvent e) {
			...
	       }

		@Override
		public void mouseMoved(MouseEvent e) {
			...
		}

		@Override
		public void mouseDragged(MouseEvent e) {
			...
		}
	}	
	
}    

Then, I was trying to register drawingCanvas as a listener for key events in the same way, but it doesnt work.... the parts I changed:

In MapTab class:

private void addDrawingCanvas() {
		drawingCanvas = new DrawingCanvas();
		addMouseListener(drawingCanvas);
		addMouseMotionListener(drawingCanvas);
		addKeyListener(drawingCanvas);
		drawingCanvas.setFocusable(true);
		add(drawingCanvas);
	        drawingCanvas.setOpaque(true);
	        drawingCanvas.setVisible(true);
}

DrawingCanvas class:

class DrawingCanvas extends JPanel implements MouseListener, MouseMotionListener, KeyListener {
...
                /* Key event handling */
		@Override
		public void keyPressed(KeyEvent e) {
			System.out.println("Pressed");
		}

		@Override
		public void keyReleased(KeyEvent e) {
			System.out.println("Released");
		}

		@Override
		public void keyTyped(KeyEvent e) {
			System.out.println("Typed Char: " + e.getKeyChar() + "Code: " + e.getKeyCode());
		}
}

What does work, however, is this:

MapTab class:

    
private void addDrawingCanvas() {
		drawingCanvas = new DrawingCanvas();
		addMouseListener(drawingCanvas);
		addMouseMotionListener(drawingCanvas);
		drawingCanvas.addKeyListener(new KeyListener(){
				public void keyPressed(KeyEvent e){
				  System.out.println("Key pressed: " + e.getKeyCode());
				  if(e.isControlDown()){
				   System.out.println("Control was pressed!");
				  }
				}
				public void keyReleased(KeyEvent e){
				  System.out.println("Key released!");
				}
				public void keyTyped(KeyEvent e){
				  System.out.println("Key Typed!");
				}   
				 
				});
		drawingCanvas.setFocusable(true);
		add(drawingCanvas);
	    drawingCanvas.setOpaque(true);
	    drawingCanvas.setVisible(true);
	}

DrawingCanvas class:

   
public void mouseClicked(MouseEvent e) {
			requestFocus(false);
                        ...
}

I don't get why the first method, which is the same as in case of mouse events, doesnt work...

would appreciate some comments, thanks!

[Michael Dunn]

> ..but I just don't understand why one way works and the other doesn't - would appreciate it if someone could explain it to me...

I see plenty of this in the code
...

what do you expect us to do with the code?
just sit there and read it, is our time worthless?

if you want a precis, at least post something that compiles.

[Veronique Kus]

Well you don't need to be rude, I only just joined the forum and don't necessarily know "the rules of not wasting your time". I actually wanted to save ppl time reading code by deleting the unrelevant parts because I thought that an experienced programmer would be able to see the problem straight away from the code.

If it helps, I'm posting the full class code below, it was enough to just ask for it in a polite way. I thought the website said "A friendly place for Java greenhorns" :-/

package mywordmaps;

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.util.ArrayList;
import java.util.Iterator;

import javax.swing.*;

public class MapTab extends Tab {
	private DrawingCanvas drawingCanvas;

	public MapTab(JTabbedPane tabbedPane, String title) {
		super(tabbedPane, title);	
		this.setLayout(new GridLayout());
		addDrawingCanvas();	
	}
	
	private void addDrawingCanvas() {
		drawingCanvas = new DrawingCanvas();
		addMouseListener(drawingCanvas);
		addMouseMotionListener(drawingCanvas);
		/*drawingCanvas.addKeyListener(new KeyListener(){
				public void keyPressed(KeyEvent e){
				  System.out.println("Key pressed: " + e.getKeyCode());
				  if(e.isControlDown()){
				   System.out.println("Control was pressed!");
				  }
				}
				public void keyReleased(KeyEvent e){
				  System.out.println("Key released!");
				}
				public void keyTyped(KeyEvent e){
				  System.out.println("Key Typed!");
				}   
				 
				});	*/
		addKeyListener(drawingCanvas);
		drawingCanvas.setFocusable(true);
		add(drawingCanvas);
	    drawingCanvas.setOpaque(true);
	    drawingCanvas.setVisible(true);
	}
	
	public void drawToolSelection(String shape){
		drawingCanvas.setCurrentShape(shape);
	}
	
	public Shape getCurrentShape(){
		return drawingCanvas.getCurrentShape();
	}
	
	class DrawingCanvas extends JPanel implements MouseListener, MouseMotionListener, KeyListener {
		private ArrayList<Shape> shapeList;
		
		private Shape currentShapeTool = null;
	    private Shape currentSelectionOutline = null;
	    private Shape draggedShape = null;
	    private Shape newShape = null;
		
		private Point sPoint = null;
	    private Point ePoint = null;
	   
	    private static final double SELECTION_OFFSET = 5.00;
	    private final float dash1[] = {5.0f};
	    private final BasicStroke dashed = new BasicStroke(1.0f, 
                BasicStroke.CAP_BUTT, 
                BasicStroke.JOIN_MITER, 
                10.0f, dash1, 0.0f);
	    private boolean selected;
	    private int dragStartedX;
	    private int dragStartedY;
	    private double dragX;
	    private double dragY;
	    private Point mouseDown,  mouseHere;
	    
	    
		public DrawingCanvas() {
			shapeList = new ArrayList<Shape>();
			this.setBackground(Color.WHITE);
			selected = false;
			requestFocus(false);
		}
		
		@Override
		public void paintComponent(Graphics g)
		{
			super.paintComponent(g);
			Graphics2D g2 = (Graphics2D)g;
			//g2.setColor(Color.green);
			for(Shape s : shapeList){
				s.draw(g2);
			}
			
			if(currentShapeTool != null){
				currentShapeTool.draw(g2);
			}
			if(currentSelectionOutline != null){
				g2.setColor(Color.GRAY);
				g2.setStroke(dashed);
				currentSelectionOutline.draw(g2);
			}
		}
		
		public void setCurrentShape(String shape)
		{
			if(shape.equals("Cursor")) {
				this.currentShapeTool = null;
			}else if(shape.equals("Rectangle")){
				this.currentShapeTool = new Rectangle();
			}else if(shape.equals("Oval")){
				this.currentShapeTool = new Oval();
			}	    
		}
		
		public Shape getCurrentShape() {
			return currentShapeTool;
		}
		
		// Mouse events handling
		public void mouseClicked(MouseEvent e) {
			setFocusable(true);
			requestFocus(false);
			selected = false;
			for(Shape s : shapeList){
				if( s.contains(e.getPoint()) == true ){
					double outlineX = s.getStartPoint().getX() - s.getWidth() - SELECTION_OFFSET;
					double outlineY = s.getStartPoint().getY() - s.getHeight() - SELECTION_OFFSET;
					currentSelectionOutline = new Rectangle(outlineX, outlineY, 
							s.getWidth() + 2*SELECTION_OFFSET, s.getHeight() + 2*SELECTION_OFFSET);
					selected = true;
					repaint();
				}
			}
			if(selected == false){
				currentSelectionOutline = null;
				repaint();
			}
			
			if(currentSelectionOutline != null) {
				checkIfChangeCursor(e);
			}
			
		}
		public void mouseEntered(MouseEvent e){}
		public void mouseExited(MouseEvent e){
		}
		public void mousePressed(MouseEvent e) {
			draggedShape = null;
			
			if(currentShapeTool != null) {
			    sPoint = e.getPoint();
			    ePoint = e.getPoint();
			    currentShapeTool.setPoints(sPoint, ePoint);
			}else{
				//check if user is trying to drag an existing shape
				for(Shape s : shapeList){
					if( s.contains(e.getPoint()) == true ){
						if(currentSelectionOutline != null &&
								currentSelectionOutline.contains(e.getPoint())) {
							draggedShape = s;
							mouseDown = e.getPoint();
							draggedShape.setOffset(mouseDown);
							if(currentSelectionOutline != null){
								currentSelectionOutline.setOffset(mouseDown);
							}
							break;
						}
					}
				}
			}
		}
		
		public void mouseReleased(MouseEvent e) {
			if(currentShapeTool != null) {
			    ePoint = e.getPoint();
			    /*Create a new shape only if it's not a single point*/
			    if(!sPoint.equals(ePoint)){
			    	/* If shape not drawn from upper left to bottom right,
				     swap relevant coordinates */
				    swapPointsIfRequired();
				    if(currentShapeTool instanceof Rectangle){
				    	 /* Create a new shape instance with the point coordinates
					     * obtained and add the newly drawn shape to the shapeLsit.
					     */
				    	newShape = new Rectangle(sPoint, ePoint);
				    	shapeList.add(newShape);
				    }else if(currentShapeTool instanceof Oval){
				    	newShape = new Oval(sPoint, ePoint);
				    	shapeList.add(newShape);
				    }	    
				    repaint();
			    }
			    
			    ePoint = null;
		    	sPoint = null;
		    	newShape = null;
			}
	    }

		@Override
		public void mouseMoved(MouseEvent e) {
			checkIfChangeCursor(e);
		}

		@Override
		public void mouseDragged(MouseEvent e) {
			if(currentShapeTool != null) {
				currentShapeTool.setEndPoint(e.getPoint());
				repaint();
			}else{
				//current tool is cursor, check if user is trying to drag a shape
				mouseHere = e.getPoint();
				if(draggedShape != null){
					draggedShape.setLocation(mouseHere);
					if(currentSelectionOutline != null){
						currentSelectionOutline.setLocation(mouseHere);
					}
					repaint();
				}
			}
		}
		
		/**
		 * Changes the cursor to move_cursor if it is hovered over the current selection outline.
		 * Otherwise sets cursor to default .
		 * @param e
		 */
		public void checkIfChangeCursor(MouseEvent e){
			if(currentSelectionOutline != null) {
				if(currentSelectionOutline.contains(e.getPoint()) == true){
					setCursor(Cursor.getPredefinedCursor(Cursor.MOVE_CURSOR));
				}else{
					setCursor(Cursor.getPredefinedCursor(Cursor.DEFAULT_CURSOR));
				}
			}
		}
		
		public void swapPointsIfRequired() {
			if(ePoint.getX() < sPoint.getX())
		    {
		      Point temp = ePoint;
		      ePoint = sPoint;
		      sPoint = temp;
		    }
		    if(ePoint.getY() < sPoint.getY())
		    {
		      int temp = (int)ePoint.getY();
		      ePoint.y = (int)sPoint.getY();
		      sPoint.y = temp;
		    }
		}
		
		@Override
		public void keyPressed(KeyEvent e) {
			System.out.println("Pressed");
		}

		@Override
		public void keyReleased(KeyEvent e) {
			System.out.println("Released");
		}

		@Override
		public void keyTyped(KeyEvent e) {
			System.out.println("Typed Char: " + e.getKeyChar() + "Code: " + e.getKeyCode());
		}
	}	
}

package mywordmaps;

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.EmptyBorder;
import javax.swing.plaf.basic.BasicButtonUI;

/** 
 * Tab class provides an abstract superclass for all tab types.
 * It sets the tab's title and add the close tab button next to the title.
 */

public abstract class Tab extends JPanel {
	private final JTabbedPane tabbedPane;
	private String tabTitle = null;
	
	public Tab(JTabbedPane tabbedPane, String title){
		this.tabbedPane = tabbedPane;
		tabTitle = title;
		tabbedPane.addTab(tabTitle, this);
		tabbedPane.setTabComponentAt(tabbedPane.indexOfComponent(this), new TabButton(tabTitle));
		this.setBackground(Color.WHITE);
		this.setBorder(new EmptyBorder(6, 6, 6, 6));
	}
	
	public String getTitleLabel(){
		return tabTitle;
	}
	
	class TabButton extends JPanel implements ActionListener {
		
		public TabButton( String labelString ){
			super(new FlowLayout());
			JLabel label = new JLabel(labelString) {
			    public String getText() {
			        int i = tabbedPane.indexOfTabComponent(TabButton.this);
				if (i != -1) {
				    return tabbedPane.getTitleAt(i);
				}
				return null;
			    }
			};
			add(label);
			JButton button = new CloseTabButton();
			button.addActionListener( this );
			button.setMargin(new Insets(0,0,0,0));
			add( button );
		}

		public void actionPerformed(ActionEvent e) {
	    	   tabbedPane.remove(tabbedPane.indexOfTabComponent( this ) );
		}
		
		
		class CloseTabButton extends JButton {//implements ActionListener {
	        public CloseTabButton() {
	            int size = 17;
	            setPreferredSize(new Dimension(size, size));
	            setToolTipText("Close tab");
	            //Make the button looks the same for all Laf's
	            setUI(new BasicButtonUI());
	            //Make it transparent
	            setContentAreaFilled(false);
	            setFocusable(false);
	            setBorder(BorderFactory.createEtchedBorder());
	            setBorderPainted(false);
	            //Making nice rollover effect
	            //we use the same listener for all buttons
	            addMouseListener(buttonMouseListener);
	            setRolloverEnabled(true);
	            //Close the proper tab by clicking the button
	            //addActionListener(this);
	        }

	       //public void actionPerformed(ActionEvent e) {
	    	 //  tabbedPane.remove(tabbedPane.indexOfTabComponent( this ) );
	       // }

	        //we don't want to update UI for this button
	        public void updateUI() {
	        }

	        //paint the cross
	        protected void paintComponent(Graphics g) {
	            super.paintComponent(g);
	            Graphics2D g2 = (Graphics2D) g.create();
	            //shift the image for pressed buttons
	            if (getModel().isPressed()) {
	                g2.translate(1, 1);
	            }
	            g2.setStroke(new BasicStroke(2));
	            g2.setColor(Color.BLACK);
	            if (getModel().isRollover()) {
	                g2.setColor(Color.RED);
	            }
	            int delta = 6;
	            g2.drawLine(delta, delta, getWidth() - delta - 1, getHeight() - delta - 1);
	            g2.drawLine(getWidth() - delta - 1, delta, delta, getHeight() - delta - 1);
	            g2.dispose();
	        }
	    
	        private final MouseListener buttonMouseListener = new MouseAdapter() {
	    	   public void mouseEntered(MouseEvent e) {
	    		   Component component = e.getComponent();
	    		   if (component instanceof AbstractButton) {
	    			   AbstractButton button = (AbstractButton) component;
	    			   button.setBorderPainted(true);
	    		   }
	    	   };

		     public void mouseExited(MouseEvent e) {
		            Component component = e.getComponent();
		            if (component instanceof AbstractButton) {
		                AbstractButton button = (AbstractButton) component;
		                button.setBorderPainted(false);
		            }
		        }
		    };
		}
	}
}

[Michael Dunn]

> Well you don't need to be rude,

not rude, just realistic.

you have a problem, lines of '...' will rarely, if ever, get a solution.

you've now posted code that many eyes can copy/paste/compile/run/see your problem,
and, hopefully, present you with a solution.

[Veronique Kus]

Maybe realistic, but unfriendly.

I actually thought that lines of "..." would make the code more readable but I'm willing to accept that they do not do any good, advice taken. Thanks.

[Rob Camick]

Actually you are correct we don't want to see all the code, but we don't want to see the "..." either.

You will find many postings that request a SSCCE, which it used to address both problems.

In general KeyEvents are not passed to a component unless it has focus and by default panels don't receive focus. One solution is to make the panel focusable, but this requires the user to click on the panel first. This is an old AWT approach.

The better solution is to use Key Bindings. This is the approach used by all Swing components. Read the section from the Swing tutorial on How to Use Key Bindings. You can also check out my little write up on Key Bindings.

[Veronique Kus]

Hi Rob, thank you for the advice about the key bindings, I've managed to implement this method in my program. Still, I am just curious why trying to implement key event handling using the KeyListener did not work even though it worked in case of the MouseListener? I mean, I set the relevant JPanel to focusable and requested focus on every click on it but it still didn't work. If anyone has any thought what was wrong with it, please let me know.