Both SystemFileChooser and Swing FileChooser open when called from event dispatching thread on Windows

[Kamik423]

For macOS reasons, I had the following code (or at least something similar) in the main method.

Timer timer =
    new Timer(
        10,
        ae -> {
          if (!MyApp.hasOpenedAnyFileYet) {
              SystemFileChooser fileChooser = new SystemFileChooser();
              fileChooser.addChoosableFileFilter(...);
              fileChooser.setFileFilter(...);
              if (fileChooser.showOpenDialog(null) == SystemFileChooser.APPROVE_OPTION) { ... }
        }});
timer.setRepeats(false);
timer.start();

On macOS, this does indeed work fine.
On Windows, this results in both a SystemFileChooser and a FlatLaf/Swing one opening.

I now circumvented this issue by not using the timer mechanism on Windows.
However, it does seem like a bug, so I wanted to report it.

[DevCharly]

Can not reproduce this with your code.
Could you provide a self-contained test app?

Are the two dialogs displayed at the same time?
Or first Windows filechooser and when closing it, then JFileChooser?

If you remove the filters, is the problem still there?

BTW if you simply want execute code on AWT thread, better use SwingUtilities.invokeLater() instead of timer.

[Kamik423]

I created an example project here: https://github.com/Kamik423/FlatLaf-1078-Demo-2025-09

Can you reproduce it now?

It works without the filters as well.

---

The reason for the timer is that I need it to have a short delay on macOS as I want to open files in the app.
This calls a callback function in the Java code.
So on program startup, I need to wait for a fraction of a second in order to see whether the callback has been completed or whether I need to show a file chooser.

[DevCharly]

Thanks for the example project.
I can reproduce it now.

With "self-contained test app" I actually meant only a complete code snippet. Not a whole project 😉
I'll post your code below so that you can remove the project repo.

package demo;

import com.formdev.flatlaf.FlatLightLaf;
import com.formdev.flatlaf.util.SystemFileChooser;

import javax.swing.*;
import java.awt.*;

public class Main {

    public static void main(String[] args) {
        FlatLightLaf.setup();
        Timer timer =
                new Timer(
                        10,
                        ae -> {
                            SystemFileChooser fileChooser = new SystemFileChooser();
                            if (fileChooser.showOpenDialog(null)
                                    == SystemFileChooser.APPROVE_OPTION) {
                                System.out.println(
                                        "Selected file: "
                                                + fileChooser.getSelectedFile().getAbsolutePath());
                            }
                        });
        timer.setRepeats(false);
        timer.start();
    }
}

[DevCharly]

The problem is caused by AWT's auto-shutdown feature.

Here is a workaround for FlatLaf 3.7:

import com.formdev.flatlaf.FlatLightLaf;
import com.formdev.flatlaf.util.SystemFileChooser;
import java.awt.Frame;
import java.awt.Window;
import javax.swing.*;

public class Main2 {

    public static void main(String[] args) {
        SwingUtilities.invokeLater( () -> {
            FlatLightLaf.setup();
            Timer timer =
                new Timer(
                        10,
                        ae -> {
                            Window dummyWindow = new Window( (Frame) null );
                            dummyWindow.addNotify();

                            SystemFileChooser fileChooser = new SystemFileChooser();
                            if (fileChooser.showOpenDialog(null)
                                    == SystemFileChooser.APPROVE_OPTION) {
                                System.out.println(
                                        "Selected file: "
                                                + fileChooser.getSelectedFile().getAbsolutePath());
                            }

                            dummyWindow.dispose();
                        });
            timer.setRepeats(false);
            timer.start();
        });
    }
}

Notes:

• new Window() ... addNotify() creates a displayable (but not shown) window that disables AWT auto-shutdown
• dummyWindow.dispose() re-enables AWT auto-shutdown, and the app quits when the system file dialog is closed
• SwingUtilities.invokeLater(...) is required on Linux; without it, the app immediately quits without showing anything

[DevCharly]

fixed in PR #1079