Why Doesn\'t My Swing Timer ActionListener Update the Text Field\'s Background Color?

Javax.swing timer Repeats, But ActionListener Does Not Execute

Introduction

In an attempt to create a flashing background color for a text field, a user encountered a peculiar issue where the timer function performed as expected, but the ActionListener did not trigger the color change. This discrepancy leaves the background color unchanged after the initial toggle.

Timer Setup

The timer setup in this scenario adheres to the industry-standard guidelines for setting up a Swing timer with a reasonable delay, repetition enablement, and an ActionListener. The timer initiates the Flash class, which implements the ActionListener interface, to handle the color changes.

ActionListener Implementation

The ActionListener, defined inside a nested static class, contains the logic for toggling the background color based on an internal boolean variable flasher. While debugging confirmed that the action is being executed, the color change is not reflected on the screen after the initial toggle.

Root Cause and Solution

The crux of the problem lies in the fact that Swing components, including text fields, require an explicit call to the repaint() method to update their appearance. Without this call, any changes made through setBackground() or other appearance-affecting methods will not be visible to the user.

Revised Implementation

To rectify the issue, the ActionListener should include a call to repaint() after altering the background color. Here's a revised version of the ActionListener:

<code class="java">static class Flash implements ActionListener {
    public void actionPerformed(ActionEvent evt) {
        if (flasher) {
            SpreademPanel.historyPnl.NameTxt.setBackground(Color.white);
        } else {
            SpreademPanel.historyPnl.NameTxt.setBackground(Color.pink);
        }
        **SpreademPanel.historyPnl.NameTxt.repaint();** // Trigger repaint
        flasher = !flasher;
    } //actionPerformed
} //Flash</code>

By adding the repaint() call, the text field will now correctly update its appearance based on the ActionListener's logic.

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