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Repainting a panel...

Posted on 1998-02-09
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Last Modified: 2010-04-16
I am having a problem with repainting a panel.  I have a main panel, and I add other panels onto it.  Depending on which selection a user chooses for how many other panels they want added to it, I need to repaint the main panel with the correct number of panels added to it.  I have a Choice component, and they select which number of panels to add, then I have a button which gets the selected number of panels to add, and clears the main panel with mainpanel.removeAll() (from Container), and then I add the new amount of panels.  It works fine except I don't see the new panel unless I resize the frame or applet first.  What is the problem and how can I correct it?
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Question by:bjg
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LVL 16

Expert Comment

by:imladris
Comment Utility
You need to call invalidate on the main panel. It is part of class Component:

public void invalidate();

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Author Comment

by:bjg
Comment Utility
It didn't work?  Where, when, and why should I call invalidate()?
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LVL 16

Expert Comment

by:imladris
Comment Utility
After the mainpanel.removeAll(), and the addition of the new panels it would be:

mainpanel.invalidate();

This will cause the panels layout manager to be called again which will cause all (new, in this case) subcomponents to be "positioned".

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Author Comment

by:bjg
Comment Utility
This is the code I have and it didn't work, the new settings only show up after I resize the applet in the appletviewer.

public void setCalendar()
      {
            currentDate.set(year, month, date);

            /*========================================================
              Find out what day of the week the first of the month
              falls on.
            ========================================================*/
            Calendar first = Calendar.getInstance();
            first.set(year, month, 1);      //Set to first day of month
            int first_day = first.get(Calendar.DAY_OF_WEEK) - 1;

            /*========================================================
              Determine total number of days in month, also check for
              leap years.
            ========================================================*/
            int totalDays = 0;
            
            if ((month == FEBRUARY) && (isLeapYear(year)))
                  totalDays = LEAP_YEAR_DAYS;
            else
                  totalDays = monthDays[month];

            /*========  Allocate correct number of DayCells for the month ======*/
            DayCell daycells[] = new DayCell[totalDays];

            canvas.removeAll();

            /*======== Add blank cells until reach first of the month ==========*/
            for (int j = 0; j < first_day; j++)
            {
                  Panel blank = new Panel();
                  blank.setBackground(Color.white);
                  canvas.add(blank);
            }

            for (int i = 0; i < 42 - first_day; i++)
            {
                  if (i < totalDays)
                  {
                        Calendar temp = Calendar.getInstance();
                        temp.set(year, month, i+1);
                        daycells[i] = new DayCell(temp);
                        daycells[i].setActionCommand("day");
                        daycells[i].addActionListener(this);
                        if ( compareDate(daycells[i].getDate(), today) )
                        {
                              daycells[i].setBackground(Color.black);
                              daycells[i].setForeground(Color.green);
                              daycells[i].requestFocus();
                        }
                        canvas.add(daycells[i]);
                  } else
                  {
                        Panel blank = new Panel();
                        blank.setBackground(Color.white);
                        canvas.add(blank);
                  }
            }
            canvas.invalidate();
      }

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LVL 16

Expert Comment

by:imladris
Comment Utility
That looks fine. The only other suggestion I can think of making is a call to repaint, i.e.

canvas.invalidate();
canvas.repaint();

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Author Comment

by:bjg
Comment Utility
I tried that, and it doesn't work either.  I can't figure it out, its stupid that it will only repaint if I resize it...
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LVL 2

Expert Comment

by:mgk
Comment Utility
Try calling validate() instead of invalidate().
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Accepted Solution

by:
rans earned 50 total points
Comment Utility

what I've done in my program was :

canvas.ivalidate();
repaint();

which means that you should not repaint canvas but the container
in which the canvas sits.
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Author Comment

by:bjg
Comment Utility
I put:

canvas.validate();
repaint();

this worked.  Thanks.
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