How to Resolve ListSelectionListener Triggering Twice in Java Swing?

Why is my ListSelectionListener being invoked twice in my Java Swing application?

JList<String> list = new JList<>(data);
list.addListSelectionListener(new ListSelectionListener() {
    @Override
    public void valueChanged(ListSelectionEvent e) {
        if (!e.getValueIsAdjusting()) {
            // Your handling code here
        }
    }
});

In Java Swing, the ListSelectionListener can be triggered multiple times during a single user interaction, which can lead to unintended behavior. This is commonly due to the way the events are propagated in the Swing event dispatch thread. To manage this effectively, it's essential to implement a mechanism that prevents multiple invocations during a single selection change.

// Example implementation that checks valueIsAdjusting
list.addListSelectionListener(new ListSelectionListener() {
    @Override
    public void valueChanged(ListSelectionEvent e) {
        if (!e.getValueIsAdjusting()) {
            // Process the selection
            int index = list.getSelectedIndex();
            System.out.println("Selected index: " + index);
        }
    }
});

Causes

• Multiple event firing during a single user action due to INTERIM updates (triggering events before the complete user action is finished).
• Improper handling of selection events without checking if the value is adjusting. The method gets called on both changes to selection and adjustments.

Solutions

• Use the getValueIsAdjusting() method to determine if the selection change is complete before executing your code within the listener.
• Implement a debouncing mechanism that ignores subsequent calls within a short time frame as a selection is made.
• Ensure that the same listener is not added multiple times inadvertently to the same component.

Mistake: Not checking getValueIsAdjusting, leading to processing incomplete events.

Solution: Always include a check for getValueIsAdjusting() before executing your logic.

Mistake: Accidentally registering the same listener multiple times on the same component.

Solution: Use a mechanism to ensure that the listener is added only once, possibly using a boolean flag or checking existing listeners.