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Thread: repaint not updating screen

  1. #1
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    Post repaint not updating screen

    Hello,
    I am really green when it comes to Java, so this is probably extremely simple, but I have been struggling with it and just can't get it right. I wrote the simple program below to try to get a handle on it, but it does not work. I am trying to add another line of text when a button is pressed, and to update it every subsequent time that the button is pressed. I am working with the code below, and it only seems to repaint and add the last line when the stop method is invoked (when I bring the window down and pull it back up). Could somebody please tell me what I am missing?
    PS. I was planning to add more functionality like different messages depending on the number entered, but I haven't gotten that far, since I couldn't even get it to update once.
    Last edited by LoganCale; April 8th, 2012 at 09:04 PM. Reason: fixed code - not properly wrapped and re-posted that part below


  2. #2
    Super Moderator Norm's Avatar
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    Default Re: repaint not updating screen

    When you change the contents of a container you must tell the container to redo the layout of the components that have been added to it. The Container class has a method you should call to tell it to redo the layout of its components.

    Please Edit your post and wrap your code with[code=java]<YOUR CODE HERE>[/code] to get highlighting
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  3. #3
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    Default Re: repaint not updating screen

    Thank you for your response. I'm sorry to be so dull (at least I'm feeling that way right now), but I tried what's below and a few other configurations and am still having the same trouble. Is this what you meant, or did I miss the boat entirely?

    import javax.swing.*;
    import java.awt.*;
    import java.awt.event.*;
    import java.awt.event.ActionEvent;
    import java.awt.event.ActionListener; 
     
    public class HelloMyFriends extends JApplet implements ActionListener 
    { 
    	 Container con = getContentPane();
         JLabel header;
    	 JTextField enterFriends;
    	 JButton btnFriend;
    	 double myCommunity; 
     
     	final int NUM_RANGES = 7;
     	int[] costRangeLimit = {1,5,25,50,200};
     	String[] status = {"you have a friend", "a good group", "It's a party", "That's a big party", "Now it's a community"};
     	String strNumFriends;
     	int numFriends;    	
     	int sub = NUM_RANGES-1;
     
     	JLabel friendStatus = new JLabel("Yes, you have a friend");
     
         public void init()  
         { 
        	 con.setLayout(new FlowLayout()); 
        	 header = new JLabel("How many friends do you have?");
             btnFriend = new JButton("Update friends");
    		 enterFriends = new JTextField ("1",6);
    		  con.add(header);
    		  con.add(enterFriends);
    		  con.add(btnFriend); 
     
              btnFriend.addActionListener(this); 
             } 
             public void paint(Graphics g) 
             { 
            	 super.paint(g);
     
            	 } 
     
            public void actionPerformed(ActionEvent e)  
             {  if (e.getSource()==btnFriend)
                  {
                      con.add(friendStatus);
                      con.repaint();
                      con.setLayout(getLayout());
                  }
     
              else if (e.getSource()!=btnFriend)  
              	 { 
                 }
                  repaint();
             }        
            public void stop()
            	{
            	repaint();
            	}
    }

  4. #4
    Super Moderator Norm's Avatar
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    Default Re: repaint not updating screen

    What method is the code calling to tell the container to do a lay out of its components?
    If you don't understand my answer, don't ignore it, ask a question.

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    Default Re: repaint not updating screen

    I thought I was using
    con.setLayout(new FlowLayout());
    for that?...

  6. #6
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    Default Re: repaint not updating screen

    That sets the layout manager. You need to call the method that tells the container to have the layout manager re do the layout.
    If you don't understand my answer, don't ignore it, ask a question.

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

    LoganCale (April 8th, 2012)

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    Default Re: repaint not updating screen

    a-ha! I was forgetting about
     con.revalidate();
    Thank you so much!

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    Default Re: repaint not updating screen

    Glad you got it to work.
    If you don't understand my answer, don't ignore it, ask a question.

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