CODEWITHSUNDEEP
javaswingjpanel
Bramble Star
Bramble Star

Reputation: 3

Java JPanel seems to not repaint after button click

I am trying to use a button to essentially replace a JPanel with another JPanel. However, when I run the code below and click on the button in the window, it displays a blank screen instead of "Instructions". I have called revalidate() and repaint() after the removeAll() method, as other people have stated in other forums, and anything I do to the window (i.e. resizing, minimizing, etc.) doesn't work.

I'm sure it's something stupid that I'm missing, but I've run out of ideas.

Thanks.

public class TitlePage extends JPanel{

private static final long serialVersionUID = 0;
private JButton a;
//The code works without me needing to define an extra JPanel instance variable.

public TitlePage(){

    setLayout(null); 
    setBackground(Color.WHITE);

    JLabel title = new JLabel("2009 AP(R) Computer Science A Diagnostic Exam");
    title.setBounds(175,100,650,50);
    title.setFont(new Font("Times New Roman", Font.PLAIN, 30));
    setVisible(true);
    add(title);


    a = new JButton("Start Diagnostic");
    a.setBounds(400, 300, 200, 50);
    a.setForeground(Color.BLUE);
    a.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent e){
            removeAll();
            revalidate();
            repaint();
            add(new Instructions());
            revalidate();
            repaint();

        }
    });
    setVisible(true);
    add(a);

    JLabel disclaimer = new JLabel("*AP(R) is a registered trademark of the College Board, which was not involved in the production of, and does not endorse, this product.");
    disclaimer.setBounds(150,650,750,50);
    disclaimer.setFont(new Font("Times New Roman", Font.PLAIN, 12));
    setVisible(true);
    add(disclaimer);

}

}

The Instructions class contains a simple JLabel.

public class Instructions extends JPanel {

private static final long serialVersionUID = 0;

public Instructions(){

    JLabel instr = new JLabel("Instructions");
    instr.setBounds(0,0,100,50);
    instr.setForeground(Color.BLACK);
    instr.setFont(new Font("Times New Roman", Font.PLAIN, 30));
    setVisible(true);
    add(instr);

}
}

Upvotes: 0

Views: 1130

Answers (1)

Jon
Jon

Reputation: 36

It depends on what you are trying to do. As I see it, you have two options. You can either change the panel within the JFrame. You can very simply do it as follows:

jframe.remove(old_panel)
jframe.add(newPanel);
jframe.revalidate();
jframe.repaint();

Options number two would be changing the contents within the panel and adding the second Panel as a sub panel. doing the following:

JPanel thisPanel = this;
a.addActionListener(new ActionListener() {
  public void actionPerformed(ActionEvent e) {
     for(Component c: thisPanel.getComponents()) {
       thisPanel.remove(c);
     }
     JPanel instruction = new Instruction();
     instruction.setBounds(your_values_here...);
     thisPanel.add(instruction);
     thisPanel.revalidate();
     thisPanel.repaint();
}

Important things to notice here are that thisPanel should be a variable set by the class and do not use 'this' within the action listener, as the 'this' in the action listener refers to the action listener object and not the JPanel.

The reason you need to use the for loop is because you do not want to remove the sub-panel you just added.

If you do not set bounds you will not see your instruction panel as it will be size of 0.

Hope this helps

Upvotes: 1

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