Re: Swing - paintComponent not called

Bojan <>
Thu, 9 Apr 2009 07:40:20 -0700 (PDT)
On Apr 8, 6:17 pm, "Matt Humphrey" <> wrote:

"Bojan" <> wrote in messagenews:c7239492-1367-41cf-a00f-=

  On Apr 8, 1:13 pm, "Matt Humphrey" <> wrote:
  > "Bojan" <> wrote in message


  > > Hi all,
  > > For some reason the paintComponent is never called to print the
  > > image. The image is valid, i have tested it with setIconImage(ima=


  > > and it worked fine. Why is the paintComponent never called? Any h=


  > > would be appreciated. Thanks in Advance.
  > > The ProgressFrame is called from a run method, which is in a clas=


  > > that implements Runnable. Which is called by creating a new threa=


  > > Here is the code for the ProgressFrame:
  > <snip>
  > Works for me--draws the image (when main added.) Are you sure busy.=

jpg is in

  > the correct location or that Resources is capitalized correctly? It=

 is best

  > also to launch the window from the EDT as in:
  > SwingUtilities.invokeLater (new Runnable () {
  > public void run () {
  > ProgressFrame pf = new ProgressFrame ();
  > }
  > });
  > Matt Humphrey

  That does work. But I forgot to mention that I am calling the method
  from actionPerformed(ActionEvent ae).

  A main frame has menu items that correspond to actions. When one o=


  them is executed it checks if ae.getSource equals to the menu item.
  JMenuItem source = (JMenuItem) ae.getSource();
  if (source == open) {
  else if (...

  When openFile is called, which creates the new thread... it does not
  show the image.
Whoa! Hold on there! This is a completely different problem.

If you're creating a new thread, there are various constraints on how you=

 can update the GUI from that thread. If you are attempting to do more t=
han repaint, revalidate or invalidate you should expect to have problems. =
 Virtually all other Swing methods must take place on the EDT.

When you say you are "calling the method from actionPerformed" do you mea=

n paintComponent or some method --as yet not shown-- which invokes new Prog=
ressFrame () ? I'm guessing the latter in which case your main problem i=
s probably threading, but if not calling paintComponent is probably the wro=
ng thing to do anyway.

You will have to show what openFile does and explain how it connects to n=

ew ProgressFrame. At this point it would probably be best if you put tog=
ether a test program that actually demonstrates the problem (as opposed to =
the code you sent that does not.)

Matt Humphrey

Here is the test code that will address my problem. I have changed
the image to an image from the internet so that everyone will have it
the same.

FILE 1: This file is the place where the image should load, it is run
in a new thread.

public class ProgressFrame extends JFrame {
    public ProgressFrame()
        Container contentPane = this.getContentPane();
        URL url = null;
        try {
            url = new URL("
        } catch (MalformedURLException e) {
        Image image = new ImageIcon( url ).getImage();
        setIconImage(image);//If the icon is changed, then so is image
should be displayed as well

        DrawingPanel panel = new DrawingPanel(image);
        setSize(384, 230);

    public void close()
        dispose(); //close the window
class DrawingPanel extends JPanel
    Image img;

    DrawingPanel (Image img)
    { this.img = img; }

    public void paintComponent (Graphics g) {
        super.paintComponent (g);
        g.drawImage (img, 0, 0, this);
    } // paintComponent

FILE 2: When the button is pressed, it creates a new thread, creates
ProgressFrame and keeps changing the title of the ProgressFrame.

public class MainFrame extends JFrame implements ActionListener{
    private String statusTitle;
    JButton button;
    public MainFrame()
        JPanel panel = new JPanel();
        button = new JButton("Start Loading");
        Container contentPane = this.getContentPane();

        setTitle("Main Frame");
        setSize(400, 200);

    public void actionPerformed(ActionEvent e) {
        if (e.getSource() == button)
            Thread a = new Thread (new Runnable () {
                public void run () {
                    ProgressFrame pf = new ProgressFrame();
                    int counter = 0;
                    //Just to show that the window is doing something
                    try {
                        while (true)
                            pf.setTitle(pf.getTitle() + ".");
                            if (counter==4)
                                counter = 0;
                    } catch (InterruptedException e) {

            statusTitle = "Loading";
            try {
                //This is supposed to represent some actions that the main class
will do
            } catch (InterruptedException e1) {


File 3 Just creates the Main Frame.:

public class Runer {
    public static void main(String[] args)
        JFrame main = new MainFrame();

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