"Multiple assemblies with equivalent identity have been imported" error for System.Windows.Forms.dll after importing unity package

[The-MAZZTer]

I suspect the error indicates this package is not compatible with Unity 2021.3.

However I have figured out how to work around it by importing a different version of System.Windows.Forms.

I copied C:\Program Files\Unity\Hub\Editor\2021.3.0f1\Editor\Data\MonoBleedingEdge\lib\mono\unityjit-win32\System.Windows.Forms.dll and replaced the DLL the SFB package provided with that one. This resolved the error and the file picker works properly (at least in the editor).

Not sure if I selected the proper DLL as there appear to be several candidates in subfolders of lib\mono. There are some that are ~700kb which I think are native code (eg not .NET binaries so Unity can't use them as such) and there are a few that are ~2-3MB which are probably workable choices. I selected one that sounded plausible and my first choice seems to be working.

[The-MAZZTer]

It looks like trying to use C:\ as the starting directory for a file open dialog does not work properly with this DLL (I did trace the problem to System.Windows.Forms). The starting directory is the default and C:\ is shown in the file name box. So that is a potential complication with this workaround.

[rafcsoares]

It looks like trying to use C:\ as the starting directory for a file open dialog does not work properly with this DLL (I did trace the problem to System.Windows.Forms). The starting directory is the default and C:\ is shown in the file name box. So that is a potential complication with this workaround.

The final solution for this problem is remove System.Windows.Forms.dll from your project and use ShellFileDialog (a wrapper to user32.dll from native c++ windows folder).

----------------- Solution Below will work with all Unity Versions (NetStandard and/or NetFramework) ---------------------------

Drop the DLL below to your unity project and remove old System.Windows.Forms.dll from your project.

DLL Link: ShellFileDialogs.zip
PS: Edit DLL Inspector in Unity to only compile dll in Editor Windows/Standalone Windows x84|x64

Replace the source of StandaloneFileBrowserWindows.cs to the code below.

#if UNITY_STANDALONE_WIN || UNITY_EDITOR_WIN

using System;
using System.IO;
using System.Runtime.InteropServices;
using System.Linq;
using System.Collections.Generic;

namespace SFB {

    // For fullscreen support
    // - "PlayerSettings/Visible In Background" should be enabled, otherwise when file dialog opened app window minimizes automatically.
    public class StandaloneFileBrowserWindows : IStandaloneFileBrowser 
    {

        [DllImport("user32.dll")]
        private static extern IntPtr GetActiveWindow();

        public string[] OpenFilePanel(string title, string directory, ExtensionFilter[] extensions, bool multiselect) {

            var shellFilters = GetShellFilterFromFileExtensionList(extensions);
            if (multiselect)
            {
                var paths = ShellFileDialogs.FileOpenDialog.ShowMultiSelectDialog(GetActiveWindow(), title, directory, string.Empty, shellFilters, null);
                return paths == null || paths.Count == 0 ? new string[0] : paths.ToArray();
            }
            else
            {
                var path = ShellFileDialogs.FileOpenDialog.ShowSingleSelectDialog(GetActiveWindow(), title, directory, string.Empty, shellFilters, null);
                return string.IsNullOrEmpty(path) ? new string[0] : new[] { path };
            }
        }

        public void OpenFilePanelAsync(string title, string directory, ExtensionFilter[] extensions, bool multiselect, Action<string[]> cb) {
            cb.Invoke(OpenFilePanel(title, directory, extensions, multiselect));
        }

        public string[] OpenFolderPanel(string title, string directory, bool multiselect) {

            var path = ShellFileDialogs.FolderBrowserDialog.ShowDialog(GetActiveWindow(), title, directory);
            return string.IsNullOrEmpty(path) ? new string[0] : new[] { path };
        }

        public void OpenFolderPanelAsync(string title, string directory, bool multiselect, Action<string[]> cb) {
            cb.Invoke(OpenFolderPanel(title, directory, multiselect));
        }

        public string SaveFilePanel(string title, string directory, string defaultName, ExtensionFilter[] extensions) {

            var finalFilename = "";
            if (!string.IsNullOrEmpty(directory))
            {
                finalFilename = GetDirectoryPath(directory);
            }

            if (!string.IsNullOrEmpty(defaultName))
            {
                finalFilename += defaultName;
            }

            var shellFilters = GetShellFilterFromFileExtensionList(extensions);
            if(shellFilters.Length > 0 && !string.IsNullOrEmpty(finalFilename))
            {
                var extension = $".{shellFilters[0].Extensions[0]}";
                if (!string.IsNullOrEmpty(extension) && !finalFilename.EndsWith(extension, StringComparison.CurrentCultureIgnoreCase))
                    finalFilename += extension;
            }
            
            var path = ShellFileDialogs.FileSaveDialog.ShowDialog(GetActiveWindow(), title, directory, finalFilename, shellFilters, 0);
            return path;
        }

        public void SaveFilePanelAsync(string title, string directory, string defaultName, ExtensionFilter[] extensions, Action<string> cb) {
            cb.Invoke(SaveFilePanel(title, directory, defaultName, extensions));
        }

        private static ShellFileDialogs.Filter[] GetShellFilterFromFileExtensionList(ExtensionFilter[] extensions)
        {
            var shellFilters = new List<ShellFileDialogs.Filter>();
            if (extensions != null)
            {
                foreach (var extension in extensions)
                {
                    if (extension.Extensions == null || extension.Extensions.Length == 0)
                        continue;

                    var displayName = extension.Name;
                    if (string.IsNullOrEmpty(displayName))
                    {
                        System.Text.StringBuilder extensionFormatted = new System.Text.StringBuilder();
                        foreach (var extensionStr in extension.Extensions)
                        {
                            if (extensionFormatted.Length > 0)
                                extensionFormatted.Append(";");
                            extensionFormatted.Append($"*.{extensionStr}");
                        }
                        displayName = $"({extensionFormatted})";
                    }
                    var filter = new ShellFileDialogs.Filter(displayName, extension.Extensions);
                    shellFilters.Add(filter);
                }
            }
            if (shellFilters.Count == 0)
            {
                shellFilters.AddRange(ShellFileDialogs.Filter.ParseWindowsFormsFilter(@"All files (*.*)|*.*"));
            }

            return shellFilters.ToArray();
        }

        private static string GetDirectoryPath(string directory) {
            var directoryPath = Path.GetFullPath(directory);
            if (!directoryPath.EndsWith("\\")) {
                directoryPath += "\\";
            }
            if (Path.GetPathRoot(directoryPath) == directoryPath) {
                return directory;
            }
            return Path.GetDirectoryName(directoryPath) + Path.DirectorySeparatorChar;
        }
    }
}

#endif

Best Regards
Rafael

[thnewlands]

Hey @rafcsoares thank you for putting this together! I'm getting a missing directive error when I follow your instructions. Do you have any troubleshooting tips?

Assets\Scripts\Thirdparty\StandaloneFileBrowser\StandaloneFileBrowserWindows.cs(78,24): error CS0246: The type or namespace name 'ShellFileDialogs' could not be found (are you missing a using directive or an assembly reference?

[rafcsoares]

You need to import dll to project buddy.

@thnewlands i put the link for dll zip in my previous comment.. you just need to drop it inside your project and select to work with UnityEditor Windows x86/x64 and Standalone Windows x86/x64

[thnewlands]

Turns out I had a competing .asmdef -- works perfectly! Thanks for sharing your solution.

[TheYellowArchitect]

Thank you for this. I was testing SFB on the editor and it was good, but days later when I built with System.Windows.Forms, I just couldn't build!

I use Unity Version 2018.1.1f1, and so, can confirm it works there. It needed .NET 4.0 though, but luckily that was the last version possible through Project Settings -> Player -> Other Settings

[Profy]

Hi @rafcsoares. I would like to know which version of ShellFileDialogs you used to make the library you gave in link. Your version does not match with the last version of ShellFileDialogs.

[rafcsoares]

@Profy i don't know... i just pick the master branch and compiled the DLL by myself to share.

In my project i use the raw code instead

[Profy]

@rafcsoares thank you for your reply. I have already contacted the developer to make some fixes.

[cmwolke-gamedesign]

It seems ShellFileDialogs doesn't respect the directory parameter, at least for me it always opens in the last location instead of where I want it to (test: BasicSampleScene, "Open file directory" button)
Edit: Can easily be fixed by running

if (!string.IsNullOrEmpty) { directory = GetDirectoryPath(directory); }