Form field actions

Often, it is useful to be able to perform some Action when the value in a form field changes. For example, to show or hide other form fields depending on the value in a combo box, or to perform some additional logic as soon as a field value changes. This is also quite easy to achieve in swing-forms!

Let's start by defining a ComboField that has some basic options:

List<String> options = new ArrayList<>();
options.add("This option has no extra settings");
options.add("This option has 1 extra setting");
options.add("This option has lot of extra settings");

ComboField<String> comboField = new ComboField<>("Show/hide extra fields:", options, 0);
formPanel.add(comboField);

Then we can define some extra fields and hide them by default:

CheckBoxField extraField1 = new CheckBoxField("Extra setting", false);
extraField1.setVisible(false);
formPanel.add(extraField1);

ShortTextField extraField2 = new ShortTextField("Extra text field 1:", 10);
extraField2.setVisible(false);
formPanel.add(extraField2);

ShortTextField extraField3 = new ShortTextField("Extra text field 2:", 10);
extraField3.setVisible(false);
formPanel.add(extraField3);

ShortTextField extraField4 = new ShortTextField("Extra text field 3:", 10);
extraField4.setVisible(false);
formPanel.add(extraField4);

Now, we can add a custom Action onto our ComboField to show or hide the extra fields depending on which combo option is selected:

comboField.addValueChangedListener(new ValueChangedListener() {
    @Override
    public void formFieldValueChanged(FormField field){
        int selectedIndex = ((ComboField)field).getSelectedIndex();
        extraField1.setVisible(selectedIndex == 1);
        extraField2.setVisible(selectedIndex == 2);
        extraField3.setVisible(selectedIndex == 2);
        extraField4.setVisible(selectedIndex == 2);
    }
});

The end result is that the "extra" fields will be shown or hidden as needed at runtime, based on what you pick in the dropdown:

Above we see the difference between selecting the different combo options. The "extra" fields that we have defined appear or disappear based on our combo box selection. We can simply use the FormField's setVisible() method in our custom Action to accomplish this!

Other uses for custom actions

We can hook a custom action onto almost any form field, in order to drive behaviour elsewhere on the form. Common uses of this are:

• Showing/hiding components depending on input (as shown above)
• Enabling/disabling components depending on input
• Pre-filling fields based on the values in other fields
• Loading additional options or data as values are selected

With an action wired up to every field on a form, you could even build a "live update" control panel that does not require an "OK" or "Submit" button, but which rather updates something elsewhere in your application as soon as the user makes a selection.