Jdialog disappears before usable

Question

I have a strange problem: From a MenuBar I (or the user) can call two actions. One does importing some data, the other deletes some data. Both are presented through a JDialog. Now the weird thing is that both share effectively the same layout and yet while the import dialogue works perfectly, the delete dialogue vanished before any interaction can happen. I do call them seperately.

For comparison consider these parts:

• the Import dialogue

 JDialog ImportFenster= new JDialog(Fenster,
                    "Import von Nutzern");

            JTextField Name= new JTextField("Vorname [Leer] Name",30);
            JFormattedTextField ID =new JFormattedTextField(
                    NumberFormat.getIntegerInstance());
            ID.setColumns(8);

            JButton Enter = new JButton("OK");
            JButton Abort =new JButton("Abbruch");
            JLabel InfoID= new JLabel("Wird keine ID angegeben, wird eine automatisch erzeugt");

            GridBagLayout ImportLayout= new GridBagLayout();
            GridBagConstraints LayoutConstraints=new GridBagConstraints();

            ImportFenster.setLayout(ImportLayout);

            LayoutConstraints.fill=GridBagConstraints.VERTICAL;
            LayoutConstraints.gridwidth=3;
            LayoutConstraints.gridx=0;
            LayoutConstraints.gridy=0;
            LayoutConstraints.ipadx=5;
            LayoutConstraints.ipady=5;
            ImportFenster.add(InfoID,LayoutConstraints);
            LayoutConstraints.gridwidth=1;
            LayoutConstraints.ipadx=10;
            LayoutConstraints.ipady=25;
            LayoutConstraints.gridx=1;
            LayoutConstraints.gridy=1;
            ImportFenster.add(ID,LayoutConstraints);
            LayoutConstraints.ipadx=10;
            LayoutConstraints.ipady=25;
            LayoutConstraints.gridx=1;
            LayoutConstraints.gridy=2;
            ImportFenster.add(Name,LayoutConstraints);
            LayoutConstraints.ipadx=10;
            LayoutConstraints.ipady=25;
            LayoutConstraints.gridx=3;
            LayoutConstraints.gridy=3;
            ImportFenster.add(Enter,LayoutConstraints);
            LayoutConstraints.ipadx=10;
            LayoutConstraints.ipady=25;
            LayoutConstraints.gridx=0;
            LayoutConstraints.gridy=3;
            ImportFenster.add(Abort,LayoutConstraints);
            LayoutConstraints.gridx=0;
            LayoutConstraints.gridy=1;
            ImportFenster.add(new JLabel("Nutzer-ID:"),LayoutConstraints);
            LayoutConstraints.gridx=0;
            LayoutConstraints.gridy=2;
            ImportFenster.add(new JLabel("Nutzer-Name:"),LayoutConstraints);


            ImportFenster.setSize(750,350);
            ImportFenster.setVisible(true);

• the delete dialogue

JDialog EntfernenFenster= new JDialog(Fenster,
                        "Löschen von Nutzern");
                JFormattedTextField ID =new JFormattedTextField(
                        NumberFormat.getIntegerInstance());
                ID.setColumns(8);
                System.out.println("Dialog:"+EntfernenFenster.isShowing());
                JButton Enter = new JButton("OK");
                JButton Abort =new JButton("Abbruch");
                System.out.println("Knöppe sind da:"+Enter.isShowing()+"\t"+Abort.isShowing());
                GridBagLayout EntfernenLayout= new GridBagLayout();
                EntfernenFenster.setLayout(EntfernenLayout);
                GridBagConstraints LayoutConstraints=new GridBagConstraints();
                LayoutConstraints.fill=GridBagConstraints.VERTICAL;
                LayoutConstraints.gridwidth=1;
                LayoutConstraints.ipadx=10;
                LayoutConstraints.ipady=25;
                LayoutConstraints.gridx=1;
                LayoutConstraints.gridy=1;
                EntfernenFenster.add(ID,LayoutConstraints);
                LayoutConstraints.ipadx=10;
                LayoutConstraints.ipady=25;
                LayoutConstraints.gridx=0;
                LayoutConstraints.gridy=1;
                EntfernenFenster.add(new JLabel("Nutzer-ID:"));
                LayoutConstraints.ipadx=10;
                LayoutConstraints.ipady=25;
                LayoutConstraints.gridx=2;
                LayoutConstraints.gridy=2;
                EntfernenFenster.add(Enter,LayoutConstraints);
                LayoutConstraints.ipadx=10;
                LayoutConstraints.ipady=25;
                LayoutConstraints.gridx=0;
                LayoutConstraints.gridy=2;
                EntfernenFenster.add(Abort,LayoutConstraints);

                EntfernenFenster.setSize(500, 200);
                EntfernenFenster.setVisible(true);

I would like to know where my mistake is. And of course how to fix this.

Answer 1

You could try to move the code of the ActionListenerer's actionPerformed to a new method void showEntfernenFenster() and do

SwingUtilities.invokeLater(() -> showEntfernenFenster());

For instance in:

JMenuItem menuItem = ...
menuItem.addActionListener(evt ->
    SwingUtilities.invokeLater(() -> showEntfernenFenster()));

actionPerformed happens on the single thread handling GUI events in the AWT queue. Then little else for the GUI can be done. AWTEventQueue.invokeLater or SwingUtilities.invokeLater (identical) will indeed call the passed "Runnable" after the actionPerformed is processed. And then again the GUI is responsive, redrawing etcetera, In general do not do long things in actionPerformed.

The why:

In order to redraw, invalidate multiple screen regions, and all in a non-parallel manner - sequentially -, many libraries across programming languages and even on operating system level use this simplifying technique: a queue of events and one thread handling them.