Holding down Next image after switching folder causes instant Crash

[EliEron]

Describe the bug
If you hold down the Next image shortcut, then switch to another folder using the built in navigation, then hold down the next image shortcut again the application will crash.

To Reproduce
Steps to reproduce the behavior:

1. Hold down next image shortcut
2. Navigate to next folder
3. Hold down next image shortcut again
4. See error

Expected behavior
The actions should work with no crash.

Additional context
I've tracked down the cause of the crash. The issue is caused by the Timer used for navigation slowdown being disposed of without being set to null:

ImageIterator.cs

private void Dispose(bool disposing, bool cleared = false)
    {
        if (_disposed)
        {
            return;
        }

        if (disposing)
        {
            _watcher?.Dispose();
            if (!cleared)
            {
                PreLoader.Clear();
            }

            _timer?.Dispose();
            PreLoader.Dispose();
        }

        _disposed = true;
        GC.SuppressFinalize(this);
    }

Which causes an ObjectDisposedException when the Timer is then used here:

private async ValueTask TimerIteration(int index, CancellationTokenSource? cts)
    {
        if (_timer is null )
        {
            _timer = new Timer
            {
                AutoReset = false,
                Enabled = true
            };
        }
        else if (_timer.Enabled)
        {
            if (!MainKeyboardShortcuts.IsKeyHeldDown)
            {
                _timer = null;
            }

            return;
        }

        _timer.Interval = TimeSpan.FromSeconds(Settings.UIProperties.NavSpeed).TotalMilliseconds;
        _timer.Start();
        await IterateToIndex(index, cts).ConfigureAwait(false);
    }

Since the timer is neither null nor initiated. The issue can be fixed by simply setting the timer to null after it is disposed in the Dispose method. But I have not looked enough at the code to see if this is the ideal fix. I only discovered this project today, so I felt it was better to just leave a bug report and let you determine the cleanest fix rather than opening a PR directly.

[Ruben2776]

Thank you for the bug report and taking the time to investigate it.

I'm currently working on rewriting and improving the Batch Resize window and its functionality. I'll take a look at this as soon as I'm done with that.

[EliEron]

Sounds good, thank you for the quick response.

I've looked for an open source image viewer with easy folder navigation and the like built-in for a bit now, it's surprisingly rare. Your viewer has pretty much every feature I've been looking for, and is written in my favorite language, so I'm quite happy with it so far👍

[Ruben2776]

I've taken a look at it, and indeed, your suggested solution works perfectly, thank you. The fix will be in the next release, which I'm planning to publish in a couple of weeks.

I'm glad that you like the folder navigation feature :)