Copying JPanel components to another JPanel - Java

marcussilfver schrieb:
> I want to copy the contents of a jPanel to another JPanel, then I want
> to empty the original JPanel.
> I unsuccessfully tried the following:
>
> jPanel1 = new JPanel();
> jPanel1.setBounds(371, 112, 364, 28);
> jPanel1.add(new JLabel("a"));
> jPanel1.add(new JLabel("b"));
> jPanel1.add(new JLabel("c"));
>
> JPanel jp = new JPanel();
>
> int numComponents = jPanel1.getComponentCount();
> System.out.println("Number of components in jPanel1 is " +
> numComponents);
>
> for (int i=0; i<numComponents; i++)
> {
> jp.add(jPanel1.getComponent(i));
Adding a Component to a Container (in this case: to jp) has a
side-effect. The Component is first removed from its previous parent, if
it is a child of any parent (in this case: of jPanel1). AWT does it that
way, to ensure that a child will never belong to more than one parent
simultaneously. This behaviour is well-hidden described in the API doc
of java.awt.Container#addImpl.
For you this means, that after your "add" operation, the "numComponents"
had become wrong, because the actual number of components now has got
smaller by 1. Also the numbering of components in jPanel1 has changed.
> }
> jPanel1.removeAll();
>
> But I get an error like this
> java.lang.ArrayIndexOutOfBoundsException: No such child: 2
> at java.awt.Container.getComponent(Unknown Source)...
>
> NOTE:
> If I replace the row inside the loop with the following row:
> System.out.println(jPanel1.getComponent(i).toString());
>
> then I dont get an exception in getComponent, I then get a correct
> standard out to the console!
>
> So how can I achieve copying JPanel components? Am I way off?
>
Try something like this:
int numComponents = jPanel1.getComponentCount();
for (int i = 0; i < numComponents; i++)
{
jp.add(jPanel1.getComponent(0));
//jPanel1.remove(...) isn't needed, because child is already removed
}
or may be like this:
for (int i = jPanel1.getNumComponents() - 1; i >= 0; i--)
{
jp.add(jPanel1.getComponent(i));
//jPanel1.remove(...) isn't needed, because child is already removed
}

--
Thomas

On Aug 14, 11:31 am, Thomas Fritsch <i.dont.like.s...@invalid.com>
wrote:
> marcussilf... schrieb:
>
> > I want to copy the contents of a jPanel to another JPanel, then I want
> > to empty the original JPanel.
> > I unsuccessfully tried the following:
>
> > jPanel1 = new JPanel();
> > jPanel1.setBounds(371, 112, 364, 28);
> > jPanel1.add(new JLabel("a"));
> > jPanel1.add(new JLabel("b"));
> > jPanel1.add(new JLabel("c"));
>
> > JPanel jp = new JPanel();
>
> > int numComponents = jPanel1.getComponentCount();
> > System.out.println("Number of components in jPanel1 is " +
> > numComponents);
>
> > for (int i=0; i<numComponents; i++)
> > {
> > jp.add(jPanel1.getComponent(i));
>
>
> Try something like this:
> int numComponents = jPanel1.getComponentCount();
> for (int i = 0; i < numComponents; i++)
> {
> jp.add(jPanel1.getComponent(0));
> //jPanel1.remove(...) isn't needed, because child is already removed
> }
> or may be like this:
> for (int i = jPanel1.getNumComponents() - 1; i >= 0; i--)
> {
> jp.add(jPanel1.getComponent(i));
> //jPanel1.remove(...) isn't needed, because child is already removed
> }
>
> --
> Thomas

For loops that change the quantity of things, I like to use a while
loop eg.

while (jPanel1.getComponentCount() > 0) {
jp.add(jPanel1.getComponent(0);
}

or I use this a lot for removing rows from a JTable

DefaultTableModel model = (DefaultTableModel)tblMyTable.getModel();
while (model.getRowCount() > 0) {
model.removeRow(0);
}

On Tue, 14 Aug 2007 marcussilfver wrote:

> I want to copy the contents of a jPanel to another JPanel, then I want
> to empty the original JPanel.

To me this whole business of moving components sounds questionable. What
are you *really* doing?

- Ville Oikarinen

"Ville Oikarinen" <ville@oikarinen.org> wrote in message
news:Pine.LNX.4.56L0.0708151532310.27727@localhost...
> On Tue, 14 Aug 2007 marcussilfver wrote:
>
>> I want to copy the contents of a jPanel to another JPanel, then I want
>> to empty the original JPanel.
>
> To me this whole business of moving components sounds questionable. What
> are you *really* doing?

Certainly there are good reasons for doing so, but if you want to
move a group of components, usually you would put them all in
one panel and just move the whole panel. This may require adding
a panel to the component hierarchy that has no other purpose than
to be the moveable container.