OpenFileDialog: load files in the same order as the user selected them

Question

I have set Multiselect to true in order to be able to load several files at once. The problem is that it ignores the order in which the user selects the files, the list of FileNames is always the same (if I select the same set of files in different order).

My question is: is it possible to achieve the desired behavior? (Store paths in the same order as selected).

List<string> filePaths = new List<string>();
Microsoft.Win32.OpenFileDialog dlg = new Microsoft.Win32.OpenFileDialog();
dlg.Multiselect = true;
dlg.DefaultExt = ".txt";
// dlg.Filter = my filter //

Nullable<bool> result = dlg.ShowDialog();
if (result == true)
{
    foreach (string file in dlg.FileNames)
    {

    }

}

Answer 1

Since OpenFileDialog is a sealed class it's probably going to require hacking in one form or another. And the way I personally would hack it is to have a polling loop that makes calls on P/Invoke in order to scrape the child window that holds the file names as they're being selected, and when that changes maintain an external list that we'll call NamesInOrder that is FIFO for any filename that is newly selected.

In this case, I first selected B then C and A.

public MainForm()
{
    InitializeComponent();
    StartPosition = FormStartPosition.CenterScreen;
    buttonOpen.Click += (sender, e) =>
    {
        ExecOpenInOrder(sender, e);
        MessageBox.Show(string.Join(Environment.NewLine, NamesInOrder), caption: "Names in Order");
    }; 
}

---

Method to show the open file dialog

private void ExecOpenInOrder(object? sender, EventArgs e)
{
    NamesInOrder.Clear();
    openFileDialog.Title = OPEN_FILE_TITLE;
    openFileDialog.InitialDirectory =
        Path.Combine(
            Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData),
            Assembly.GetEntryAssembly().GetName().Name
    );
    Directory.CreateDirectory(openFileDialog.InitialDirectory);
    openFileDialog.Multiselect = true;
    var dialogResult = DialogResult.None;
    localStartPollForChanges();
    openFileDialog.ShowDialog();
    .
    .
    .
}
List<string> NamesInOrder { get; } = new List<string>();

Detecting hWnd for OpenFileDialog

Although the caption of OpenFileDialog reads "Open" by default, calling GetWindowText returns empty unless we explicitly set a recognizable value, in this case using const string OPEN_FILE_TITLE = "Open". Once we obtain it, we're going to enumerate its child windows.

    async void localStartPollForChanges()
    {
        while (dialogResult == DialogResult.None)
        {
            var hWndParent = GetForegroundWindow();
            StringBuilder sb = new StringBuilder(MAX_STRING);
            if (hWndParent != IntPtr.Zero)
            {
                GetWindowText(hWndParent, sb, MAX_STRING);
            }
            Debug.WriteLine($"\nForeground window title: {sb}");
            if (sb.ToString() == OPEN_FILE_TITLE)
            {
                EnumChildWindows(hWndParent, localEnumChildWindowCallback, IntPtr.Zero);
            }
            await Task.Delay(TimeSpan.FromSeconds(0.1));
        }
    }

Find the correct child window and read its text

We're looking for a child window whose class is ""ComboBoxEx32".

    bool localEnumChildWindowCallback(IntPtr hWnd, IntPtr lParam)
    {
        StringBuilder className = new StringBuilder(MAX_STRING);
        GetClassName(hWnd, className, MAX_STRING);

        if (className.ToString() == "ComboBoxEx32")
        {
            StringBuilder windowText = new StringBuilder(MAX_STRING);
            GetWindowText(hWnd, windowText, MAX_STRING);

            // Detect multiselect
            var names = localGetNames(windowText.ToString());
            foreach (var name in NamesInOrder.ToArray())
            {
                if(!names.Contains(name))
                {
                    // Remove any names that aren't in new selection
                    NamesInOrder.Remove(name);
                }
            }
            foreach (var name in names.ToArray())
            {
                // If NamesInOrder doesn't already hold the name, add it to the end.
                if (!NamesInOrder.Contains(name))
                {
                    NamesInOrder.Add(name);
                }
            }
            Debug.WriteLine(string.Join(Environment.NewLine, NamesInOrder));
            return false;
        }
        return true;
    }

Extract the file names

When this window text is retrieved, use a RegEx to separate multiple file names where names are in quotes and separated by a space.

    string[] localGetNames(string text)
    {
        string[] names =
                Regex
                .Matches(text.ToString(), pattern: @"""(.*?)\""")
                .Select(_ => _.Value.Trim(@"""".ToCharArray()))
                .ToArray();
        // But it there's only one name, the pattern
        // will never 'hit' so return the single name 
        return names.Any() ? names : new string[] { text };
    }