Javafx create dialog on lost focus crashes the app when closing window

Question

In a JavaFX stage, I want to validate user input when the focus leaves a textfield. If the user input is not a valid age (0 to 120), then a Dialog using ControlsFX Dialogs with an error message is displayed.

Here's the code:

participantAgeTextField.focusedProperty()
                       .addListener(new ChangeListener<Boolean>() {
        @Override
        public void changed(ObservableValue<? extends Boolean> ov,
                            Boolean oldPropertyValue, Boolean newPropertyValue)
        {
            if( !newPropertyValue ) {  // lost focus
                if( !participantAgeTextField.getText().isEmpty() ) {
                    if ( participantAgeTextField.getText().matches("^\\d+$")) {
                        int val = Integer.
                                   parseInt(participantAgeTextField.getText());
                        if( val <= 0 ) {
                            val = 1;
                        } else if( val > 120 ) {
                            val = 120;
                        }
                        participantAgeTextField.setText(""+val);
                    } else {
                        participantAgeTextField.setText("");
                        Dialogs.create()
                            .owner(null)
                            .title("Error")
                            .masthead(null)
                            .message("You must enter a valid age!")
                            .showError();
                    }
                }
            }
        }
    });

This works fine, except when a user enters an invalid value, and then tries to close the window by clicking the "X" button in the top right corner of the window (stage).

In this case the application 'hangs'. (Strangely enough only in Windows, does not happen in Linux).

I have been looking for a fix, like not displaying the message when the focus changes to the window's "X". However I did not find a way to detect this.

Other ideas how to fix this would be greatly appreciated!

Joris

EDIT Probably ControlsFX causes the crash. I cannot use JavaFX dialogs (introduced in 8u40) because I'm using Javafx 8u25. Any alternatives welcomed!

EDIT 2 The crash can be avoided by not using ControlsFX Dialogs but creating the error message 'by hand' as suggested by DVarga. But this causes the error message to show up after the window has been closed. Any ideas on how to prevent that from happening?

Have you tried with standard JavaFX `Alert`? `Alert alert = new Alert(AlertType.ERROR); alert.setContentText("You must enter a valid age!"); alert.setTitle("Error"); alert.showAndWait();` — DVarga, Jun 09 '16 at 11:36
Good suggestion, but unfortunately I am bound to JavaFX 8u25 (legacy code) and Alert was introduced in 8u40. — DeBaze, Jun 09 '16 at 11:40
My mistake. I should have pointed this out in the first place.. — DeBaze, Jun 09 '16 at 11:41
You could take a look on this: https://github.com/BertelSpA/openjfx-dialogs-jdk7. Or as last hope, "implement" your own dialog: http://stackoverflow.com/questions/8309981/how-to-create-and-show-common-dialog-error-warning-confirmation-in-javafx-2 — DVarga, Jun 09 '16 at 11:42
I followed the second suggestion and quickly implemented my own dialog. Now the app does not crash anymore. However the dialog is still displayed after I close the window. — DeBaze, Jun 09 '16 at 11:50

score 0 · Answer 1 · answered Jun 09 '16 at 12:06

I think I will circumvent the crash as follows:

In stead of showing a "popup" dialog window after loss of focus in case of wrong input, I will display an error message next to the input box in red. On re-gaining focus I can then remove the error message.

Javafx create dialog on lost focus crashes the app when closing window

1 Answers1