重新验证和重新绘制不起作用

Question

import java.awt.*;
import javax.swing.*;

public class Class4 {

    public static final long serialVersionUID = 1L;

    public void mainMethod(int event){
        JFrame f = new JFrame("Love Test");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setSize(500,200);     
        f.setLayout(new GridBagLayout());

        GridBagConstraints gbc = new GridBagConstraints();

        if(event == 0){




            JPanel p = new JPanel();
            p.setLayout(new BoxLayout(p,BoxLayout.Y_AXIS));
            p.setBounds(150, 0, 500, 75);
            p.setPreferredSize(new Dimension(150,75));
            JTextField boy = new JTextField();
            boy.setMaximumSize(new Dimension(200,40));
            JTextField girl = new JTextField();
            girl.setMaximumSize(new Dimension(200,40));
            p.add(boy);
            p.add(girl);
            gbc.insets = new Insets(-90,310,0,0);
            gbc.gridx = 0;
            gbc.gridy = 0;
            f.add(p,gbc);

            JPanel p3 = new JPanel(new BorderLayout());
            p3.setBounds(0, 0, 150, 75);
            p3.setPreferredSize(new Dimension(150,75));
            Class5 c5o = new Class5();
            c5o.setPreferredSize(new Dimension(150,75));
            p3.add(c5o);
            gbc.insets = new Insets(0,0,90,330);
            gbc.gridx = 0;
            gbc.gridy = 0;
            f.add(p3,gbc);

            JPanel p2 = new JPanel(new FlowLayout());
            Class7 c7o = new Class7();
            p2.add(c7o);
            p2.setPreferredSize(new Dimension(300,40));
            gbc.insets = new Insets(0,0,-20,0);
            gbc.gridx = 0;
            gbc.gridy = 0;
            f.add(p2,gbc);

            f.setVisible(true);

            //1st
            JOptionPane.showMessageDialog(null,f.isVisible());


        }

        if(event == 5){

            JPanel p4 = new JPanel(new BorderLayout());
            p4.setBounds(0,140,500,55);
            Class2 c2o = new Class2();
            Dimension d2 = new Dimension(500,55);
            c2o.setPreferredSize(d2);
            p4.setPreferredSize(d2);
            p4.add(c2o);
            gbc.insets = new Insets(0,0,-130,0);
            gbc.gridx = 0;
            gbc.gridy = 0;  
            f.add(p4,gbc);

            f.invalidate();
            f.validate();
            f.repaint();

            //2nd
            JOptionPane.showMessageDialog(null,f.isVisible());
        }

    }

}

The revalidate and repaint doesn't work. I have an layout manager, so I suspect the problem is with the if statements. The 1st time I test the visibility of f, it returned true. The second time I tested the same thing, it returned false. Why doesn't my revalidate and repaint work? How I need to do to get it to work?

Answer 1

 if(event == 5){

        JPanel p4 = new JPanel(new BorderLayout());
        p4.setBounds(0,140,500,55);
        Class2 c2o = new Class2();
        Dimension d2 = new Dimension(500,55);
        c2o.setPreferredSize(d2);
        p4.setPreferredSize(d2);
        p4.add(c2o);
        gbc.insets = new Insets(0,0,-130,0);
        gbc.gridx = 0;
        gbc.gridy = 0;  
        f.add(p4,gbc);

        f.invalidate();
        f.validate();
        f.repaint();

        //2nd
        JOptionPane.showMessageDialog(null,f.isVisible());
    }

The frame f it isn't visible(missing the f.setVisible(true); ), so not need to be revalidated and repainted in this case, it will not be visible for user. Also use a logger or a breakpoint to test f.isVisible() because that will block the ui.

Answer 2

There are some issues with this code, but the major one is the scope of your JFrame reference f .

Assumed that you are calling the method somehow like in this main sample:

public static void main(String[] args) {
  Class4 c = new Class4();
  c.mainMethod(0);
  c.mainMethod(5);
}

Then, your code is creating a second JFrame during the second call.

Move the JFrame creation into the constructor and make f a member variable:

public class Class4 {

    private JFrame f;

    public Class4() {
       f = new JFrame("Love Test");
       f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
       f.setSize(500,200);     
       f.setLayout(new GridBagLayout());
    }

    // ...
}

You can then modify the JFrame in subsequent calls of the mainMethod() .

Some additional notes:

• Avoid reusing GridBagConstraints . Create them through the constructor. This makes the code much more robust.
• You do not need to get the contentPane from the JFrame anymore (as suggested in an other answer). As of Java 1.5, the add() methods of JFrame directly delegate to the content pane.
• There is no need to do invalidate() or repaint() when adding components to the JFrame . add() already invalidates the component hierarchy. However, you need to call validate() when the component has already been shown (as in your case). See java.awt.Container.add() for more information.

Answer 3

I'm having trouble seeing exactly what you're looking for. An SSCCE would really help. Is this what you're looking for?

import java.awt.*;
import javax.swing.*;

class Canv extends JComponent {

    GridBagConstraints gbc;

    public Canv (int event) {

        gbc = new GridBagConstraints();

        switch(event)
        {
            case 0:
                this.setLayout(new BoxLayout(this,BoxLayout.Y_AXIS));
                this.setBounds(150, 0, 500, 75);
                this.setPreferredSize(new Dimension(150,75));
                JTextField boy = new JTextField();
                boy.setMaximumSize(new Dimension(200,40));
                JTextField girl = new JTextField();
                girl.setMaximumSize(new Dimension(200,40));
                this.add(boy);
                this.add(girl);
                gbc.insets = new Insets(-90,310,0,0);
                gbc.gridx = 0;
                gbc.gridy = 0;
                this.add(this,gbc);

                JPanel p3 = new JPanel(new BorderLayout());
                p3.setBounds(0, 0, 150, 75);
                p3.setPreferredSize(new Dimension(150,75));
                //Class5 c5o = new Class5();
                //c5o.setPreferredSize(new Dimension(150,75));
                //p3.add(c5o);
                gbc.insets = new Insets(0,0,90,330);
                gbc.gridx = 0;
                gbc.gridy = 0;
                this.add(p3,gbc);

                JPanel p2 = new JPanel(new FlowLayout());
                //Class7 c7o = new Class7();
                //p2.add(c7o);
                p2.setPreferredSize(new Dimension(300,40));
                gbc.insets = new Insets(0,0,-20,0);
                gbc.gridx = 0;
                gbc.gridy = 0;
                this.add(p2,gbc);
                break;
            case 5:
                JPanel p4 = new JPanel(new BorderLayout());
                p4.setBounds(0,140,500,55);
                //Class2 c2o = new Class2();
                Dimension d2 = new Dimension(500,55);
                //c2o.setPreferredSize(d2);
                p4.setPreferredSize(d2);
                //p4.add(c2o);
                gbc.insets = new Insets(0,0,-130,0);
                gbc.gridx = 0;
                gbc.gridy = 0;  
                this.add(p4,gbc);

                //this.invalidate();
                this.validate();
                this.repaint();

                JOptionPane.showMessageDialog(null,this.isVisible());
                break;
            default:
                break;
        }
    }

    public void paintComponent(){

    }


}

public class Class4 {

    static int event;
    static JFrame frame;
    static Canv canvas;

    public static void main(String[] args)
    {
        frame = new JFrame("Love Test");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(500,200);     
        frame.setLayout(new GridBagLayout());
        //event = Integer.parseInt(args[0]);
        event = 5;
        canvas = new Canv(event);
        frame.add(canvas);
        frame.setVisible(true);
    }
}

Running the above code would return true in the dialog box. In order to change between events, just add another method in Class4 to reset Canv, by calling its constructor with a different event number.