problem painting

[Derek Boring]

I have a JFrame that contains a JPanel (tbox), and a JScrollPane (vPort) which displays the contents of another JPanel (view). The problem is when I draw on 'view' tbox does not repaint and the scrollbars on vPort do not repaint, they show whatever is behind the JFrame. The drawing is done in the JFrame's 'paint' event. I've tried calling the 'repaint()' methods for 'tbox' and 'vPort' at the end of the event and the componets repaint, but then it doesn't show what is drawn in view.

When no repaints are called:


When 'tbox.repaint()' is called:


When 'vPort.repaint()' is called:


When both are repainted:

[Craig Wood]

The drawing is done in the JFrame's 'paint' event.
This is not the recommended way to draw in a top–level container. Better to use a JPanel or
JComponent that is dedicated to graphic display. Here is an example.

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import javax.swing.*;
 
public class FrameDrawing implements ActionListener {
    FrameDrawingPanel topPanel;
    FrameDrawingPanel bottomPanel;
 
    public void actionPerformed(ActionEvent e) {
        topPanel.toggleScale();
        bottomPanel.toggleScale();
    }
 
    private JPanel getGraphicContent() {
        Dimension d = new Dimension(300,100);
        topPanel = new FrameDrawingPanel(1.1, d);
 
        d = new Dimension(400,400);
        bottomPanel = new FrameDrawingPanel(0.9, d);
 
        JScrollPane scrollPane = new JScrollPane(bottomPanel);
        d = new Dimension(400,300);
        scrollPane.setPreferredSize(d);
 
        JPanel panel = new JPanel(new BorderLayout());
        panel.add(topPanel, "First");
        panel.add(scrollPane);
        return panel;
    }
 
    private JPanel getControl() {
        JButton button = new JButton("scale");
        button.addActionListener(this);
        JPanel panel = new JPanel();
        panel.add(button);
        return panel;
    }
 
    public static void main(String[] args) {
        FrameDrawing test = new FrameDrawing();
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(test.getGraphicContent());
        f.getContentPane().add(test.getControl(), "Last");
        f.pack();
        f.setLocation(200,100);
        f.setVisible(true);
    }
}
 
class FrameDrawingPanel extends JPanel {
    double scale;
 
    public FrameDrawingPanel(double scale, Dimension d) {
        this.scale = scale;
        setPreferredSize(d);
    }
 
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D)g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                            RenderingHints.VALUE_ANTIALIAS_ON);
        int w = getWidth();
        int h = getHeight();
        int d = Math.min(w,h)/4;
        Ellipse2D.Double e = new Ellipse2D.Double(w/2-d,h/2-d,2*d,2*d);
        Rectangle r = e.getBounds();
        double x = (1.0 - scale)*r.getCenterX();
        double y = (1.0 - scale)*r.getCenterY();
        AffineTransform at = AffineTransform.getTranslateInstance(x,y);
        at.scale(scale,scale);
        g2.draw(at.createTransformedShape(e));
    }
 
    public void toggleScale() {
        if(scale < 1.0)
            scale = 1.1;
        else
            scale = 0.9;
        repaint();
    }
}

[Derek Boring]

Thanks, that helps alot.

[Nathan Pruett]

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