Java Swing按钮消失

Question

I am trying to make an invisible button where the painted button is, but when I try to add the button, it disappear almost every time I run the program and when its visible it goes invisible on resize. Please help me, whats wrong?

import javax.imageio.ImageIO;
import javax.swing.*;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.Font;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.Image;
import java.io.IOException;

public class Main extends JFrame
{
    public static final int VERSION = 1;
    private static final long serialVersionUID = 1L;
    private Image img;
    private boolean hasMouseListener = false;
    private Image bgImage;

    public static int ii;
    public static int jj;


    public Main() throws IOException
    {
        super("Unigin Alpha 1.0.0"); //Set title


        ii = this.getWidth();
        jj = this.getHeight();

        setBackground(Color.WHITE);
        //loginForm1 = new LoginForm(this);
        JPanel localJPanel = new JPanel();
        //localJPanel.setLayout(null);
        setVisible(true); 
        setTitle("Unigin");

        setDefaultCloseOperation(EXIT_ON_CLOSE);
        localJPanel.setPreferredSize(new Dimension(854, 480));

        setLayout(new FlowLayout());
        add(localJPanel, "Center");

        //-------------------------------------------------------------------------
        JButton bb = new JButton("HEEL");
        localJPanel.add(bb, "CENTER");
        //bb.setLocation(getWidth()/2-76-8, getHeight()/2); Doesn't work!
        //i / 2 - 76 - 8, j / 2, 76, 20

        pack();
        setLocationRelativeTo(null);
        try
        {
          setIconImage(ImageIO.read(Main.class.getResource("favicon.png")));
        } catch (IOException localIOException) {
          localIOException.printStackTrace();
        }

        super.paint(getGraphics());
    }





    public void paint(Graphics paramGraphics)
      {
        try {
            bgImage = ImageIO.read(Main.class.getResource("wool_red.png")).getScaledInstance(32, 32, 16);
          } catch (IOException localIOException) {
            localIOException.printStackTrace();
          }

        int i = getWidth() / 2;
        int j = getHeight() / 2;
        if ((img == null) || (img.getWidth(null) != i) || (img.getHeight(null) != j)) {
          img = createVolatileImage(i, j);
        }

        Graphics localGraphics = img.getGraphics();
        for (int k = 0; k <= i / 32; k++)
          for (int m = 0; m <= j / 32; m++)
            localGraphics.drawImage(bgImage, k * 32, m * 32, null);
        String str;
        FontMetrics localFontMetrics;

        if (true) {
          if (!hasMouseListener) {
            hasMouseListener = true;
            //addMouseListener(this);
          }
          localGraphics.setColor(Color.WHITE);
          str = "Bukkit Unigin";
          localGraphics.setFont(new Font(null, 1, 20));
          localFontMetrics = localGraphics.getFontMetrics();
          localGraphics.drawString(str, i / 2 - localFontMetrics.stringWidth(str) / 2, j / 2 - localFontMetrics.getHeight() * 2);

          localGraphics.setColor(Color.LIGHT_GRAY);
          localGraphics.setFont(new Font(null, 0, 12));
          localFontMetrics = localGraphics.getFontMetrics();

          localGraphics.setColor(Color.LIGHT_GRAY);


          localGraphics.fill3DRect(i / 2 - 76 - 8, j / 2, 76, 20, true);
          localGraphics.fill3DRect(i / 2 + 8, j / 2, 76, 20, true);
          //localGraphics.fill3DRect(x,y,width,height,true);

          localGraphics.setColor(Color.WHITE);
          str = "What do you want to do?";
          localGraphics.drawString(str, i / 2 - localFontMetrics.stringWidth(str) / 2, j / 2 - 8);

          localGraphics.setColor(Color.BLACK);
          str = "New plugin";
          localGraphics.drawString(str, i / 2 - 56 - 18 - localFontMetrics.stringWidth(str) / 2 + 28, j / 2 + 14);
          str = "Load plugin";
          localGraphics.drawString(str, i / 2 + 18 - localFontMetrics.stringWidth(str) / 2 + 28, j / 2 + 14);
        }

        localGraphics.dispose();
        paramGraphics.drawImage(img, 0, 0, i * 2, j * 2, null);


      }

    public static void main(String[] args) throws IOException {

        new Main();



    }
}

Answer 1

The painting will disappear when you resize the frame because you aren't overriding the paintComponent of a JComponent you have a method named paint that runs once when called by the constructor.

Instead break out your application into separate classes that each handle less responsibility. One of which needs to override paintComponent() to actually draw the button.

Follow the Swing Tutorial for custom painting: http://docs.oracle.com/javase/tutorial/uiswing/painting/

Answer 2

If you want to make an invisible JButton.

JButton invisibleButton = new JButton(){
     @Override
     protected void paintComponent(Graphics g){}; 
};

Answer 3

Fix 1:

Remove super.paint(getGraphics()); from constructor.

Reason: You should never do it. Use of repaint() is recommended although none is needed in this case.

---

Fix 2:

Call super.paint(g) at the end of overridden paint method.

Reason: This method is responsible for drawing children (Your button in this case). Button won't appear if you don't call it every time the frame is painted.

---

Fix3:

Call setBackGround(new java.awt.Color(0, 0, 0, 0)); in the constructor.

Reason: If you don't do this, the super.paint(g); would erase everything you painted manually.

---

Personally I'd suggest using a JPanel for custom painting. It's painting mechanism is much cleaner (Separate paintComponent, paintBorder, paintChildren methods).

Good luck.

Answer 4

• Don't use getGraphics , it unreliable and this is not how custom painting is done
• Don't call paint yourself, ever. You are not responsible for performing painting operations, that's the responsibility of the RepaintManager
• Don't break the paint chain, always call super.paintXxx when overriding paint methods. The painting process is a complex series of chained method calls which work together to generate the output. You should avoid overriding paint of top level containers, top level containers are a complex series of components, overriding paint can easily break this design as you have done here. They are also not double buffered
• Avoid loading resources within any paintXxx method or performing any time consuming operations. Paint operations are intended to return quickly. Failing to do so will slow the repaint process noticeably.

Basically, by breaking the paint chain, you've prevented the paint process from being able to render the child components of the frame. You would run into issues even if you did call super.paint , as you would either paint over the top of what was previously painted or the paint process would clear what you painted before it...(not to mention that JFrame has at least three layers of other containers sitting on top of it before you even add anything to it)

Start by separating your program logic. Focus on the needs of you "image", rendering to a custom component, extending from something like JPanel , but overriding it's paintComponent method.

Add this to your frame (may as the content pane). Add your other controls to it.

Take a look at Performing Custom Painting and Painting in AWT and Swing for more details about how painting works and How to use root panes to understand the complex nature of top level containers in Swing