Re: A Swing question about readable control-flow

Daniele Futtorovic <>
Thu, 24 Jul 2008 16:12:00 +0200
On 24/07/2008 08:43, Leo Breebaart allegedly wrote:

Daniele Futtorovic <> writes:

Unless I'm mistaken, and if QuestionnaireDialog extends
JDialog, then you simply have to specify the dialog as /modal/

I apologise, I simplified my use case a little bit too much in
order to present it here concisely.

Making the JDialog (which is indeed the QuestionnaireDialog's
base class) modal indeed goes a long way towards what I want --
but I want a bit more.

In reality, my application has a number of these Actions. I want
the user to be able to continue to select other Actions, even if
he or she is not yet finished with the current one.

If I make the dialog modal, the main window becomes inaccessible
and no other buttons can be clicked. If I set the ModalityType of
my QuestionnaireDialog to DOCUMENT_TYPE, I *almost* get what I
want. Now I can indeed start multiple actions (and I take care to
disable the originating Action as long as its Questionnaire is
showing, so you can not start the same action twice), but
unfortunately the last-started Questionnaire will always be the
only available to user input. You cannot select any of the
earlier Questionnaire dialogs -- they are visible, but disabled.
You can start multiple actions, but you have to unwind the dialog
stack one by one.

If I could solve that one remaining problem, life would be

Either way, thanks for your response -- much appreciated.

I see. I might note that your design may be a bit awkward (in terms of
"good UI design"), and may confuse some users. You might want to look
for better ways to visually represent the flow you envision.

Anyway, making the Dialog modal would have been the legacy way of having
the code wait until it's closed for the processing to resume, but the
basic idea is very simple anyway:

public interface ResultHolder<E extends Object> {
     void setResult(E e);

     E getResult();

public static class BlockingDialogWithResult<E extends Object>
extends JDialog
    private final ResultHolder<E> resultHolder;

    protected BlockingDialogWithReturnValue(Frame parent,
ResultHolder<E> rh){

       if( rh == null )
          throw new IllegalArgumentException(new NullPointerException());

       resultHolder = rh;


    private void init0(){
          new WindowAdapter(){
             public void windowClosed(WindowEvent e){
                synchronized( resultHolder ){
                   resultHolder.setResult( getResultValue() );

    public abstract E getResultValue();

public static Object showBlockingDialogAndGetResult(final Frame parent){
    final ResultHolder<Object> rh = new

       new Runnable() {
          public void run(){
             BlockingDialogWithResult<Object> d = new
SomeBlockingDialogWithResultImplementation<Object>(parent, rh);


    synchronized( rh ){

    return rh.getResult();

Something like that, anyway (code is from scratch, untested,
uncompiled). Note: you'll have to invoke the static method above from
elsewhere than the EDT.


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