在 Java 中的主 window 上画线

Question

I'm trying to draw line on main window without creation a new window as it is in most examples which I found. I have created a new project in NetBeans 8.1, added new JPanel and put two buttons in Design mode. Something like this:

public class NewJPanel extends javax.swing.JPanel {

    /**
     * Creates new form NewJPanel
     */
    public NewJPanel() {
        initComponents();
    }

    /**
     * This method is called from within the constructor to initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is always
     * regenerated by the Form Editor.
     */
    @SuppressWarnings("unchecked")
    . . . .
    private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
        // TODO add your handling code here:
    }                                        

    private void jButton2ActionPerformed(java.awt.event.ActionEvent evt) {                                         
        // TODO add your handling code here:
    }                                        


    // Variables declaration - do not modify                     
    private javax.swing.JButton jButton1;
    private javax.swing.JButton jButton2;
    // End of variables declaration                   
}

I would like to draw the line (10,10,100,100) by pressing Buttom1 and clean it by pressing Bottom2. I will so appreciate the simplest example. Thanks a lot!

Answer 1

You can use the paint method to draw 2D graphics in JPanel, to achieve your functionality create a boolean variable drawLine and set it to true for button1 and false for button2 as follows:

    private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
        drawLine = true;
        repaint();
    }

    private void jButton2ActionPerformed(java.awt.event.ActionEvent evt) {
        // TODO add your handling code here:
        drawLine = false;
        repaint();
    }

    // Variables declaration - do not modify
    private javax.swing.JButton jButton1;
    private javax.swing.JButton jButton2;
    private boolean drawLine = false;

Now Override the paint method in your panel and add following code to display line and clear it out if drawLine is false:

@Override
    public void paint(Graphics arg0) {
        super.paint(arg0);
        Graphics2D gd = (Graphics2D) arg0;
        if(drawLine){
            gd.setColor(Color.RED);
            gd.drawLine(10, 10, 100, 100);
        }else{
            super.paint(arg0);
        }
    }

In this way, you can draw line by pressing button1 and clear it out with button2.