The test case below illustrates the problem. Try clicking on the radio buttons to add/remove the components in a BorderLayout panel.

For example, initially, all five zones are shown. Click on the Add/Remove North
radio button and both the North and Center zones disappear.


import java.applet.Applet;
import java.awt.*;
 
public class Test extends Applet
{
        static Frame f;
        Button btnNorth = new Button ("North");
        Button btnSouth = new Button ("South");
        Button btnEast = new Button ("East");
        Button btnWest = new Button ("West");
        Button btnCenter = new Button ("Center");
 
        Checkbox c = new Checkbox ("Add/Remove North");
        Checkbox c1 = new Checkbox ("Add/Remove South");
        Checkbox c2 = new Checkbox ("Add/Remove East");
        Checkbox c3 = new Checkbox ("Add/Remove West");
        Checkbox c4 = new Checkbox ("Add/Remove Center");
 
        Panel borderPanel = new Panel ();
        Panel chkboxPanel = new Panel ();
 
        public void init ()
        {
                borderPanel.setLayout (new BorderLayout());
 
                add (btnNorth, "North");
                add (btnSouth, "South");
                add (btnEast, "East");
                add (btnWest, "West");
                add (btnCenter, "Center");
 
                chkboxPanel.setLayout (new GridLayout(0,1));
                chkboxPanel.add (c);
                chkboxPanel.add (c1);
                chkboxPanel.add (c2);
                chkboxPanel.add (c3);
                chkboxPanel.add (c4);
 
                add (borderPanel);
                add (chkboxPanel);
        }
         public void start ()
        {
                //System.out.println ("layout="+getLayout().toString());
        }
 
        public boolean handleEvent (Event e)
        {
                if (e.target == c)
                {
                        if (c.getState ()) //true => remove ..
                                remove (btnNorth);
                        else // false => add
                                add (btnNorth, "North");
                }
 
                if (e.target == c1)
                {
                        if (c1.getState ()) //true => remove ..
                                remove (btnSouth);
                        else // false => add
                                add (btnSouth, "South");
                }
 
                if (e.target == c2)
                {
                        if (c2.getState ()) //true => remove ..
                                remove (btnEast);
                        else // false => add
                                add (btnEast, "East");
                }
                if (e.target == c3)
                {
                        if (c3.getState ()) //true => remove ..
                                remove (btnWest);
                        else // false => add
                                add (btnWest, "West");
                }
                if (e.target == c4)
                {
                        if (c4.getState ()) //true => remove ..
                                remove (btnCenter);
                        else // false => add
                                add (btnCenter, "Center");
                }
                return false;
 
        }
 
        public void remove (Button b)
        {
                BorderLayout lb = (BorderLayout) borderPanel.getLayout();
                //lb.removeLayoutComponent(b);
                borderPanel.remove (b);
                validate ();
        }
 
        public void add (Button b, String s)
        {
                borderPanel.add (b);
                BorderLayout lb = (BorderLayout) borderPanel.getLayout();
                lb.addLayoutComponent(b, s);
                validate ();
        }
        public static void main (String args [])
        {
                Test t = new Test ();
                f = new Frame ();
                f.add (t);
                t.init();
                f.show ();
                f.resize (100,100);
                t.start ();
        }
}


brent.christian@eng 1999-06-28