Re: Java swing JPanel messed up

From:

Daniel Pitts <newsgroup.spamfilter@virtualinfinity.net>

Newsgroups:

comp.lang.java.gui

Date:

Thu, 09 Apr 2009 08:43:58 -0700

Message-ID:

<49de1876$0$3632$7836cce5@newsrazor.net>

Ian Shef wrote:

Daniel Pitts <newsgroup.spamfilter@virtualinfinity.net> wrote in
news:49dcc231$0$22339$7836cce5@newsrazor.net:

dom.k.black@googlemail.com wrote:

Hi,

I have a prototype, very simple Swing app. It consists of a MainFrame
with a JPanel based component.

I override the JPanel paintComponent() method to plot some data. This
involves quite a few floating point calculations, but not enough to
cause a noticeable delay (ie a small fraction of a second).

It works fine, until I resize the window (causing the JPanel to
resize). Then it messes up, some parts of the plot are correct, some
are displaced upwards in the Y direction. It definitely does a redraw.

I added a button which calls repaint() on the panel. If I press that,
the plot is fine again.

Is there anything I need to do when I resize? Should I call repaint()
after a resize? Is there an onResize event?

Regards

Dom

Make sure you're doing all the drawing on the EDT. If you start a new
Thread at any time, you might be doing things unsafely.

You are correct, of course, but perhaps you missed that dom.k.black wrote
that he overrode paintComponent() ?

I did not miss that, but that fact alone doesn't mean the code doesn't
call paintComponent on the wrong thread.

Without an SSCCE, we can't really help you.
(see <http://sscce.org/>)

So true. However, I wonder if dom.k.black is following all of the rules for
paintComponent, such as calling super (or completely filling the background).

Not *all* of the rules are being followed, or there wouldn't be a
problem. The most common rule broken that results in this behavior is
threading safety, so that's why I suggested it first.

Still waiting for the OP to post code...

--
Daniel Pitts' Tech Blog: <http://virtualinfinity.net/wordpress/>