Associating a File Extension and Context Menus with an Application in the Registry

Published Fri, Jun 11 2004 16:31 | coad

You can easily assign a file extension to open with your application in the registry.

Verbal Description
The extension is added as a key under "HKEY_CLASSES_ROOT" with the (default) value set to the file's type (a string arbitrarily assigned by yourself). Then you add a key with the file's type also to "HKEY_CLASSES_ROOT" with its (default) value set to the file's type description (that is shown in Exporer). Under the same key, add they keys "shell/open/command" with the (default) value being the program to execute. Use "%1" with the quotes to pass the file's name to your app. You can also assign an icon by adding a "DefaultIcon" key under the file's type key. Then additional context menu items can be added by putting keys the [filetype]/shell/[MenuItem]/Command

Example Registry Entries

  • HKEY_CLASSES_ROOT\.npost = NovaBlog.Post
  • HKEY_CLASSES_ROOT\NovaBlog.Post = NovaBlog Article Posting
  • HKEY_CLASSES_ROOT\NovaBlog.Post\DefaultIcon = C:\Program Files\NovaBlog\NovaBlox.exe,0
  • HKEY_CLASSES_ROOT\NovaBlog.Post\shell\Open = &Open
  • HKEY_CLASSES_ROOT\NovaBlog.Post\shell\Open\Command = C:\Program Files\NovaBlog\NovaBlox.exe "%1"
  • HKEY_CLASSES_ROOT\NovaBlog.Post\shell\PostNow = &Post the Article Now
  • HKEY_CLASSES_ROOT\NovaBlog.Post\shell\PostNow\Command = C:\Program Files\NovaBlog\NovaBlox.exe /postnow "%1"

C# Code
Thankfully there is a Microsoft.Win32 namespace with classes for working with the registry. This is all there is to it!

// Created by Noah Coad, 6/11/04

using Microsoft.Win32;
using System.Windows.Forms;

public static void CreateRegEntries()
{
  RegistryKey rkey = Registry.ClassesRoot;
  rkey.CreateSubKey(".npost").SetValue("", "NovaBlog.Post");
  rkey = rkey.CreateSubKey("NovaBlog.Post");
  rkey.SetValue("", "NovaBlog Article Post");
  rkey.CreateSubKey("DefaultIcon").SetValue("", Application.ExecutablePath + ",0");
  rkey = rkey.CreateSubKey("shell");
  
  RegistryKey keycmd = rkey.CreateSubKey("Open");
  keycmd.SetValue("", "&Open");
  keycmd.CreateSubKey("Command").SetValue("",
    "\"" + Application.ExecutablePath + "\" \"%1\"");
  
  keycmd = rkey.CreateSubKey("PostNow");
  keycmd.SetValue("", "&Post Article Now");
  keycmd.CreateSubKey("Command").SetValue("",
    "\"" + Application.ExecutablePath + "\" /postnow \"%1\"");
}

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Comments

# coad said on June 14, 2004 10:43 PM:

It's more difficult if you try to grab the TIF association, though. After some digging I had to change the Explorer FileExts key, but I'm still not sure I did it right.

# syncter said on December 29, 2005 5:05 AM:


Thanks for useful code snippet.

If I would like to use a different DefaultIcon other than current defaulted in the application, let's say in a resource assembly file (myResource.dll contains multiple icon files), how can I identify the resource ID it should point to?


rkey.CreateSubKey("DefaultIcon").SetValue("mypath/myResource.dll" + ",?");

Thanks.