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Thread: addActionListener to JButton

  1. #1
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    Default addActionListener to JButton

    Hello,

    I'm trying to write a method that makes a JButton and adds actionlistener but it doesn't work.
    The code below is written in a Class that extends JPanel implements ActionListener.

    I tried to replace "this" with instance of class but that also didn't work. Can somebody help me out, I wrote this to understand
    how addActionListener works. But I can't figure it out

    Thanks in advance!

    	public void setButton(JButton knop, String naam)
    	{
    		knop = new JButton(naam);
    		knop.setBackground(Color.LIGHT_GRAY);
    		knop.setForeground(Color.BLACK);
    		knop.setFont(new Font("Ariel", Font.PLAIN, 20));
    		knop.addActionListener(this); <<<<<<-----
    		this.add(knop);
    	}


  2. #2
    Super Moderator Norm's Avatar
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    Default Re: addActionListener to JButton

    it doesn't work
    Please explain what "doesn't work"means.
    Copy the full text of any error messages and paste it here,
    If you don't understand my answer, don't ignore it, ask a question.

  3. #3
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    Default Re: addActionListener to JButton

    It doesnt give an error message, the ActionListener just doesn't work. When I click a button it does nothing..

    Thank you for your response!

    public class MainMenu extends JPanel implements ActionListener
    {
    	private JButton PLAY, HELP, CREDITS, EXIT, knop;
    	private Image Background;
     
    	public MainMenu()
    	{
    		setButton(PLAY, "Play");
    		setButton(HELP, "Help");
    		setButton(CREDITS, "Credits");
    		setButton(EXIT, "Exit");
     
    		Background = new ImageIcon("C:\\projectJava\\MenuBG.jpg").getImage();
    	}
     
    	public JButton setButton(JButton knop, String naam)
    	{
    		knop = new JButton(naam);
    		knop.setBackground(Color.LIGHT_GRAY);
    		knop.setForeground(Color.BLACK);
    		knop.setFont(new Font("Ariel", Font.PLAIN, 20));
    		knop.addActionListener(this);
    		knop.setSize(350,350);
    		knop.setAlignmentX(CENTER_ALIGNMENT);
    		knop.setAlignmentY(CENTER_ALIGNMENT);
    		this.add(Box.createRigidArea(new Dimension(0,20)));
    		this.add(knop);
    		return knop;
    	}
     
    	public void paintComponent(Graphics g)
    	{
    		super.paintComponents(g);
    		g.drawImage(Background,0,0,null);
    	}
     
    	public void actionPerformed(ActionEvent e) 
    	{
    		if(e.getSource() == PLAY)
    		{
    			System.out.println("hello");
    		}
    		else if(e.getSource()==HELP)
    		{
     
    		}
    		else if(e.getSource()==CREDITS)
    		{
    			System.out.println("werkt");
    		}
    		if(e.getSource()==knop)
    		{
    			System.out.println("Hello");
    		}
    	}
     
    }

  4. #4
    Super Moderator Norm's Avatar
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    Default Re: addActionListener to JButton

    Add a println statement to the listener method that prints a message when it is called and also prints out the value of e
    so you can see if it is executed and what the contents of the event object is.
    If you don't understand my answer, don't ignore it, ask a question.

  5. #5
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    Default Re: addActionListener to JButton

    If I modify the constructor like this (with JButton knop) the ActionListener works and does print "Hello" like it is written in the actionPerformed method.
    so from that I can see that the problem should be with that setButton method where I addActionListener(THIS), I think the problem is with that THIS.

    Could it be? I'm not sure because I have no clue how to make it work otherwise

    Thank you for your response

    public MainMenu()
    	{
                    knop = new JButton("Help")
                    knop.addActionListener(this);
                    this.add(knop);
     
    		setButton(PLAY, "Play");
    		setButton(HELP, "Help");
    		setButton(CREDITS, "Credits");
    		setButton(EXIT, "Exit");
     
    		Background = new ImageIcon("C:\\projectJava\\MenuBG.jpg").getImage();
    	}

  6. #6
    Super Moderator Norm's Avatar
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    Default Re: addActionListener to JButton

    If the listener called OK now, what is the code in the listener method supposed to do?

    think the problem is with that THIS.
    What is the problem now?
    If you don't understand my answer, don't ignore it, ask a question.

  7. #7
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    Default Re: addActionListener to JButton

    When I click a button, suppose PLAY, it should print out "hello". It doesn't do that, so I think the THIS in knop.addActionListener(THIS) is for the ActionListener and is supposed to be written in the constructor. Am I correct?

  8. #8
    Super Moderator Norm's Avatar
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    Default Re: addActionListener to JButton

    The this variable can be used in any non static method in a class.

    You need to make a small, complete program that compiles, executes and shows the problem. There small pieces of code that you've posted are not enough to show the problem.
    If you don't understand my answer, don't ignore it, ask a question.

  9. The Following User Says Thank You to Norm For This Useful Post:

    ICEPower (April 5th, 2013)

  10. #9
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    Default Re: addActionListener to JButton

    I don't think I understand the problem, but I also don't really understand what you're saying about a program that shows the problem. I'm kind of really new to Java.
    Thank you for the help though!

  11. #10
    Super Moderator Norm's Avatar
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    Default Re: addActionListener to JButton

    I was asking for a program that will compile, execute and show the problem. Without that I can't say what is happening.
    If you don't understand my answer, don't ignore it, ask a question.

  12. #11
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    Default Re: addActionListener to JButton

    The only other class I've made is a JFrame to show a GUI, except that I haven't written any other program.
    I still don't understand why it doesn't recognize actionperformed for the Button but I found another way to fix it

    I made another class ButtonListener implements ActionListener and an actionPerformed in that class which will handle the buttonclick.
    In my MainMenu class, in setButton method I've written knop.addActionListener(new ButtonListener()).

    And that works

  13. #12
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    Default Re: addActionListener to JButton

    Mark this as solved then.
    If you don't understand my answer, don't ignore it, ask a question.

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