to add Scrollbar to Frame in AWT

[Jatin sachdev]

I want a scrollbar in my awt frame.
In my frame i have used paint(graphics g) option
when the painting goes beyond the specified size it is not displaying.I want a scrollbar to see that.

for e.g.

size(300,300)---frame

and we have rectangle starting at x=400 and y=400

to see this rectangle i need a scrollbar

[Stephan van Hulst]

Why are you using AWT, and not Swing?

Anyway, you can do this by adding a ScrollPane to your frame. Then, add a Canvas to your ScrollPane, to which you draw whatever it is you want to draw.

You should call setPreferredSize() on the Canvas as the data you want to draw requires it.

[Jatin sachdev]

Its not working.....

i have wasted my 6 hours on this please help...

Add.java

class Add extends Canvas
{
       Add() {}
       public void paint(Graphics g)
      {
      // dont know the size it takes.It can go upto any height.
      }
}

Graph.java

class Graph extends JFrame
{
	Graph() 
        {
         	Container contentpane=getContentPane();
		Add canvas=new Add(bound,a);
		JScrollPane jscrollpane=new JScrollPane(canvas,ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS,ScrollPaneConstants.HORIZONTAL_SCROLLBAR_AS_NEEDED);
		contentpane.add(jscrollpane); 
		setVisible(true);
		setSize(600,600);
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
	
        }

When i run this Graph.java Scroll does not work
Please help me in this.

Since paint in Canvas can go beyond the set size of JFrame i want scrolling

Now this has seriously become a Headache.
Also suggest a good book for swing to learn.

[Rob Spoor]

Stephan mentioned ScrollPane, not JScrollPane. The former is an AWT component, the second a Swing component. You shouldn't mix AWT and Swing components.

But I repeat his question: Why are you using AWT, and not Swing? Replace the Canvas with a JPanel in which you override paintComponent. Just make sure to call super.paintComponent(g) as the first statement.

[Stephan van Hulst]

Check out the Swing tutorials:
http://download.oracle.com/javase/tutorial/uiswing/
http://download.oracle.com/javase/tutorial/ui/features/index.html

Anyway, regarding your problem. First of all, don't mix Swing and AWT components with eachother. Either use one or the other. If you're going to use Swing, extend a JPanel instead of a Canvas.
Also, when you use Swing, make sure to override paintComponent(Graphics), instead of paint(Graphics), or you will run into a lot of trouble. [edit] Rob mentioned all of this [/edit]

Now, you base your painting on some data, right? You can't paint if you don't know what to paint. Usually, you draw stuff depending on some fields you would have in your Add class. Now, this means that whenever you update your fields when the painting method has to draw something else, you should also be able to determine how big the painting is going to be. Then you update the preferred size of your component based on this information, and you revalidate the scroll pane.

Here are two examples, one for AWT, one for Swing:

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

final class PaintAWT extends Canvas {

  @Override
  public void paint(Graphics g) {
    int dim = 20;
    int width = (int) Math.ceil(getWidth() / dim);
    int height = (int) Math.ceil(getHeight() / dim);

    g.setColor(Color.BLUE);
    for (int y = 0; y <= height; y++)
      for (int x = 0; x <= width; x++)
        if ((x + y) % 2 == 0)
          g.fillRect(x * dim, y * dim, dim, dim);
  }

  public static void main(String... args) {
    final Frame frame = new Frame("AWT form");
    frame.addWindowListener(new WindowAdapter() {
      @Override
      public void windowClosing(WindowEvent e) {
        frame.dispose();
      }
    });

    final ScrollPane pane = new ScrollPane();
    frame.add(pane);

    final PaintAWT canvas = new PaintAWT();
    pane.add(canvas);
    frame.setSize(200, 200);
    frame.setVisible(true);

    try {
      Thread.sleep(6000);
    } catch (InterruptedException ex) {
      //
    }

    EventQueue.invokeLater(new Runnable() {
      public void run() {
        canvas.setPreferredSize(new Dimension(400, 400));
        pane.invalidate();
        pane.validate();
      }
    });
  }
}

final class PaintSwing extends JPanel {

  @Override
  protected void paintComponent(Graphics g) {
    super.paintComponent(g);

    int dim = 20;
    int width = (int) Math.ceil(getWidth() / dim);
    int height = (int) Math.ceil(getHeight() / dim);

    g.setColor(Color.RED);
    for (int y = 0; y <= height; y++)
      for (int x = 0; x <= width; x++)
        if ((x + y) % 2 == 0)
          g.fillRect(x * dim, y * dim, dim, dim);
  }

  public static void main(String... args) {
    JFrame frame = new JFrame("Swing form");
    frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

    final JScrollPane pane = new JScrollPane();
    frame.add(pane);

    final PaintSwing canvas = new PaintSwing();
    pane.setViewportView(canvas);
    frame.setSize(200, 200);
    frame.setVisible(true);

    try {
      Thread.sleep(6000);
    } catch (InterruptedException ex) {
      //
    }

    SwingUtilities.invokeLater(new Runnable() {
      public void run() {
        canvas.setPreferredSize(new Dimension(400, 400));
        pane.revalidate();
      }
    });
  }
}

final class Test {
  public static void main(final String... args) {
    new Thread(new Runnable() {
      public void run() {
        PaintSwing.main(args);
      }
    }).start();

    PaintAWT.main(args);
  }
}

[Jatin sachdev]

Thanks a ton

Its now working....................yeahhhhhhhhhhhhhhhh.....