MsixContextMenuHandler

MsixContextMenuHandler

A config-driven C++ DLL that adds entries to the classic Windows context menu ("Show more options" on Windows 11) from within an MSIX package.

Minimum OS: Windows 11 21H2 (Build 22000). On Windows 10 the required desktop9 manifest extension is silently ignored by the shell — the handler is never loaded.

Companion to MsixModernContextMenuHandler which targets the Windows 11 primary context menu (no extra click) instead.

Why this exists

Classic shell extensions (IContextMenu) inside MSIX packages are registered as com:SurrogateServer, which means Windows hosts them in dllhost.exe. That process has no MSIX activation context, so the DLL cannot find the packaged executable through the VFS — menu entries appear but do nothing when clicked.

This DLL is registered as com:InProcessServer so it runs inside explorer.exe with full MSIX activation context. It reads its configuration from a JSON file next to the DLL, needing no registry access at all.

What it does

• Implements IShellExtInit, IContextMenu, IContextMenu2, IContextMenu3
• Reads menu entries, icons, and the target executable from MsixContextMenuHandler.json
• Builds dynamic menu labels based on the selected files (e.g. "Add to 'archive.rar'")
• Launches the configured application via CreateProcess or optionally via a PSF launcher
• Works for files, folders, folder backgrounds — controlled by the JSON config

Platform support

OS	Build	Behaviour
Windows 11 21H2	22000	Appears under "Show more options" (secondary menu, extra click required)
Windows 11 22H2	22621	Same
Windows 11 23H2+	22631+	Same
Windows 10 (any)	—	desktop9:fileExplorerClassicContextMenuHandler silently ignored — handler never called

desktop9 was introduced with Windows 11. On Windows 10 the manifest remains valid (packaging does not fail), but the shell never activates the handler.

For the Windows 11 primary context menu (no extra click needed), use MsixModernContextMenuHandler instead.

Building

Requirements: Visual Studio 2022, Windows SDK 10.0.22000+, C++17.

.\Build-ContextMenuHandler.ps1          # increments patch version, builds Release|x64
.\Build-ContextMenuHandler.ps1 -Clean   # clean build

Output: bin\Release\MsixContextMenuHandler.dll

Config file

Place MsixContextMenuHandler.json next to the DLL in the package. Example:

{
  "clsid": "{YOUR-GUID-HERE}",
  "menuTitle": "MyApp",
  "executable": "VFS\\ProgramFilesX64\\MyApp\\MyApp.exe",
  "icon": "VFS\\ProgramFilesX64\\MyApp\\MyApp.exe",
  "iconIndex": 0,
  "archiveExtension": ".zip",
  "allFiles": true,
  "folders": true,
  "background": false,
  "entries": [
    {
      "id": "addToZip",
      "label": "Add to ZIP archive",
      "labelWithFile": "Add to \"{archive}.zip\"",
      "args": "a \"{folder}\\{archive}.zip\" {files}",
      "filesOnly": false,
      "extensions": []
    },
    {
      "id": "extractHere",
      "label": "Extract here",
      "args": "x {files} \"{folder}\\\"",
      "filesOnly": true,
      "extensions": [".zip", ".rar", ".7z"]
    }
  ]
}

Placeholders in args and labelWithFile

Placeholder	Replaced with
{archive}	Stem of the selected file + archiveExtension; for multiple files: parent folder name
{files}	Space-separated quoted full paths of all selected items
{folder}	Parent folder of the first selected item

MSIX manifest

Generate a unique CLSID for your package and add to AppxManifest.xml:

<com:Extension Category="windows.comServer">
  <com:ComServer>
    <com:InProcessServer>
      <com:Path>MsixContextMenuHandler.dll</com:Path>
      <com:Class Id="YOUR-GUID-HERE" ThreadingModel="Apartment"/>
    </com:InProcessServer>
  </com:ComServer>
</com:Extension>

<desktop9:Extension Category="windows.fileExplorerClassicContextMenuHandler">
  <desktop9:FileExplorerClassicContextMenuHandler>
    <desktop9:Clsid>{YOUR-GUID-HERE}</desktop9:Clsid>
  </desktop9:FileExplorerClassicContextMenuHandler>
</desktop9:Extension>

Required namespace declarations on <Package>:

• xmlns:com="http://schemas.microsoft.com/appx/manifest/com/windows10"
• xmlns:desktop9="http://schemas.microsoft.com/appx/manifest/desktop/windows10/9"

Testing outside MSIX

# 1. Build Release|x64 (copies DLL to Test\)

# 2. Place the target executable (e.g. WinRAR.exe) in Test\ so relative paths resolve.

# 3. Install (requires admin for HKLM):
.\Test\Install-ContextMenuHandler.ps1 -RestartExplorer

# 4. Right-click a file -> "Show more options" -> your submenu.

# 5. Uninstall:
.\Test\Uninstall-ContextMenuHandler.ps1 -RestartExplorer

PSF

The DLL itself requires no PSF. If the application it launches needs PSF fixups (RegLegacy, MFR), set "psfLauncher" in the JSON to route invocations through PSFLauncher:

{
  "psfLauncher": "MYAPP_PsfLauncherA.exe",
  ...
}

When psfLauncher is empty or absent, the application is launched directly.

License

Copyright (c) 2026 Andreas Nick. Use at your own risk — no warranty, no support obligations. See LICENSE.