How Can I Programmatically Associate File Extensions with Executables in C#?

Associating a file extension with an executable file in C#

C# itself does not have a built-in API to manage file associations. However, you can leverage the Registry API to access and modify the Windows registry because file association information is stored in the registry.

To associate a specific file extension with your executable, you need to create a registry key under HKEY_CLASSES_ROOT.

1. Create a subkey of file extension:

   • Create a subkey under HKEY_CLASSES_ROOT named with the file extension (e.g., .txt).
   • Set the default value of this subkey to a unique name for your file type, such as "Acme.TextFile".

2. Create file type subkey:

   • Create a subkey under HKEY_CLASSES_ROOT with the name used in the previous step (for example, "Acme.TextFile").

3. Set default icon:

   • Add a subkey named "DefaultIcon" under the file type subkey.
   • Set the default value of "DefaultIcon" to the path and index of the icon to use.

4. Add context menu action:

   • Create a subkey named "shell" under the file type subkey.

   • Under the "shell" subkey, create subkeys for each context menu action you want to add.

   • Sets the default value of each action subitem to the following string:

     • "executable_path" "%1"
     • Replace "executable_path" with the path to the executable file and "%1" with the placeholder for the file path passed as argument.

For example, to associate a .txt file with EmEditor, you need to create the following registry key:

<code>[HKEY_CLASSES_ROOT\.txt]
@="emeditor.txt"

[HKEY_CLASSES_ROOT\emeditor.txt]
@="Text Document"

[HKEY_CLASSES_ROOT\emeditor.txt\DefaultIcon]
@="%SystemRoot%\SysWow64\imageres.dll,-102"

[HKEY_CLASSES_ROOT\emeditor.txt\shell]

[HKEY_CLASSES_ROOT\emeditor.txt\shell\open]

[HKEY_CLASSES_ROOT\emeditor.txt\shell\open\command]
@="\"C:\Program Files\EmEditor\EMEDITOR.EXE\" \"%1\""

[HKEY_CLASSES_ROOT\emeditor.txt\shell\print]

[HKEY_CLASSES_ROOT\emeditor.txt\shell\print\command]
@="\"C:\Program Files\EmEditor\EMEDITOR.EXE\" /p \"%1\""</code>

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