Java Usage of JScrollPane

 
/*
 * ScrollTest.java
 *
 * Created on August 4, 2003, 11:01 AM
 * "finalized August 6, 2003, but note that it took hours and hours to
 * find the setPreferred... required.
 * Note also that some text stolen from other sources, including SUN,
 * without attribution (lost?).
 */

/**
 *
 * @author  Carl W. David
 */

//The following imports were demanded by various calls,
//but could have been avoided if one was willing to write something like
//java.awt.event.WindowListener rather than just WindowListener in the implements section (below).

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


public class ScrollTest extends javax.swing.JFrame implements WindowListener,ActionListener{

//I had to add the "implements WindowListener" after the fact, since
// the IDE added a WindowListener (see below), and the program wouldn't compile
// after that!

    private MyPanel drawingPanel;
    private Container contentPane;
    
    // public int ox, oy, x, y;
    
    /** Creates new form ScrollTest */
    public ScrollTest() {
        initComponents();
        setSize(400,400);

//Here, the drawingPanel is set larger than the size of the JFrame which
//contains it.

        drawingPanel = new MyPanel(1000,1000)i;

//Here, the fact that the thing to be drawn is bigger than the enclosing
//JScrollPane is made apparent to the enclosing JScrollPane.

        drawingPanel.setPreferredSize(new Dimension(1000,1000));
        jScrollPane1.setViewportView(drawingPanel);

//Here the Listener is attuned to the Scrolling Events both Horizontal
//and Vertical

        AdjustmentListener listener = new MyAdjustmentListener();
        jScrollPane1.getHorizontalScrollBar().addAdjustmentListener(listener);
        jScrollPane1.getVerticalScrollBar().addAdjustmentListener(listener);

//and we're done.

    }
    
    
    /** 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.
     */

    private void initComponents() {//GEN-BEGIN:initComponents
        jButton1 = new javax.swing.JButton();
        jScrollPane1 = new javax.swing.JScrollPane();

        getContentPane().setLayout(new javax.swing.BoxLayout(getContentPane(), javax.swing.BoxLayout.X_AXIS));

//Here is the WindowListener that the IDE added

        addWindowListener(this);

        jButton1.setText("press to redraw");
        jButton1.addActionListener(this);

        getContentPane().add(jButton1);

        jScrollPane1.setHorizontalScrollBarPolicy(javax.swing.JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
        jScrollPane1.setVerticalScrollBarPolicy(javax.swing.JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
        getContentPane().add(jScrollPane1);

        pack();
    }

    // Code for dispatching events from components to event handlers.

    public void actionPerformed(java.awt.event.ActionEvent evt) {
        if (evt.getSource() == jButton1) {
            ScrollTest.this.jButton1ActionPerformed(evt);
        }
    }

    public void windowActivated(java.awt.event.WindowEvent evt) {
    }

    public void windowClosed(java.awt.event.WindowEvent evt) {
    }

    public void windowClosing(java.awt.event.WindowEvent evt) {
        if (evt.getSource() == ScrollTest.this) {
            ScrollTest.this.exitForm(evt);
        }
    }

    public void windowDeactivated(java.awt.event.WindowEvent evt) {
    }

    public void windowDeiconified(java.awt.event.WindowEvent evt) {
    }

    public void windowIconified(java.awt.event.WindowEvent evt) {
    }

    public void windowOpened(java.awt.event.WindowEvent evt) {
    }//GEN-END:initComponents
    
    private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {//GEN-FIRST:event_jButton1ActionPerformed
        // Add your handling code here:
        jScrollPane1.revalidate();
    }//GEN-LAST:event_jButton1ActionPerformed
    
    /** Exit the Application */
    private void exitForm(java.awt.event.WindowEvent evt) {//GEN-FIRST:event_exitForm
        System.exit(0);
    }//GEN-LAST:event_exitForm
    
    /**
     * @param args the command line arguments
     */
    public static void main(String args[]) {
        new ScrollTest().show();
    }
    
    public void adjustmentValueChanged(AdjustmentEvent e) {
        System.out.println("adjustmentValueChanged");
    }
    
    // Variables declaration - do not modify//GEN-BEGIN:variables
    private javax.swing.JButton jButton1;
    private javax.swing.JScrollPane jScrollPane1;
    // End of variables declaration//GEN-END:variables


}

//the following was literally taken from the SUN jswing tutorial
//except for some printing


class MyAdjustmentListener implements AdjustmentListener {
    // This method is called whenever the value of a scrollbar is changed,
    // either by the user or programmatically.
    public void adjustmentValueChanged(AdjustmentEvent evt) {
        Adjustable source = evt.getAdjustable();
        System.out.println("MyAdjustmentListener(AdjustmentListener)");
        // getValueIsAdjusting() returns true if the user is currently
        // dragging the scrollbar's knob and has not picked a final value
        if (evt.getValueIsAdjusting()) {
            // The user is dragging the knob
            System.out.println("The user is using the knob");
            return;
        }
        
        // Determine which scrollbar fired the event
        int orient = source.getOrientation();
        if (orient == Adjustable.HORIZONTAL) {
            // Event from horizontal scrollbar
        } else {
            // Event from vertical scrollbar
        }
        
        // Determine the type of event
        int type = evt.getAdjustmentType();
        System.out.println("type = "+type);
        switch (type) {
            case AdjustmentEvent.UNIT_INCREMENT:
                // Scrollbar was increased by one unit
                break;
            case AdjustmentEvent.UNIT_DECREMENT:
                // Scrollbar was decreased by one unit
                break;
            case AdjustmentEvent.BLOCK_INCREMENT:
                // Scrollbar was increased by one block
                break;
            case AdjustmentEvent.BLOCK_DECREMENT:
                // Scrollbar was decreased by one block
                break;
            case AdjustmentEvent.TRACK:
                // The knob on the scrollbar was dragged
                break;
        }
        
        // Get current value
        int value = evt.getValue();
    }
}


//That's the end of the stuff from SUN.
//What I learned (below) is that one needs to create a JPanel, or Canvas, or 
//something, WHOSE PAINT METHOD ADDRESSES just that part(!), which is why we have
to do it!


class MyPanel  extends JPanel{
    
    protected MyPanel(int width, int height){
        this.setSize(width,height);
    }//end of protected MyPanel
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        
        // Retrieve the graphics context; this object is used to paint shapes
        Graphics2D g2d = (Graphics2D)g;
        // Draw an oval that fills the window
        

        int width = this.getBounds().width;
        int height = this.getBounds().height;
        
        
        g2d.drawOval(10,20, 300,400);
        // and Draw a diagonal line that fills MyPanel
        g2d.drawLine(0,0,width,height);
    }//end of paint
}//end of class MyPanel

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