How to Reliably Associate File Extensions with Applications in C#?

Associating File Extensions with Applications

Problem:

As a software developer, you want to allow users to set your application as the default editor for a specific file type. However, your current method doesn't seem to function correctly.

Response:

The provided method may encounter issues if:

• Your application is not running with elevated privileges.
• Your method doesn't properly set the necessary registry keys under HKEY_CURRENT_USER.

An alternative implementation that addresses these concerns:

public class FileAssociation
{
    public string Extension { get; set; }
    public string ProgId { get; set; }
    public string FileTypeDescription { get; set; }
    public string ExecutableFilePath { get; set; }
}

public static class FileAssociations
{
    static FileAssociations()
    {
        SetDllDirectory(Path.GetDirectoryName(Process.GetCurrentProcess().MainModule.FileName));
    }

    [DllImport("shell32.dll", CharSet = CharSet.Unicode)]
    extern static int SHChangeNotify(int wEventId, int uFlags, IntPtr dwItem1, IntPtr dwItem2);
    const int SHCNE_ASSOCCHANGED = 0x8000000;
    const int SHCNF_FLUSH = 0x1000;

    public static void EnsureAssociationsSet(params FileAssociation[] associations)
    {
        var changesMade = false;
        foreach (var association in associations)
        {
            changesMade |= SetAssociation(
                association.Extension,
                association.ProgId,
                association.FileTypeDescription,
                association.ExecutableFilePath);
        }

        if (changesMade)
            SHChangeNotify(SHCNE_ASSOCCHANGED, SHCNF_FLUSH, IntPtr.Zero, IntPtr.Zero);
    }

    public static bool SetAssociation(string extension, string progId, string fileTypeDescription, string applicationFilePath)
    {
        var changesMade = false;
        using (RegistryKey extensionKey = RegistryKey.CurrentUser.CreateSubKey($@"Software\Classes\{extension}"))
        {
            changesMade |= SetKeyDefaultValue(extensionKey, null, progId);
        }

        using (RegistryKey progIdKey = RegistryKey.CurrentUser.CreateSubKey($@"Software\Classes\{progId}"))
        {
            changesMade |= SetKeyDefaultValue(progIdKey, null, fileTypeDescription);
            changesMade |= SetKeyDefaultValue(progIdKey.CreateSubKey(@"shell\open\command"), null, $"\"{applicationFilePath}\" \"%1\"");
        }

        return changesMade;
    }

    static bool SetKeyDefaultValue(RegistryKey key, string name, object value)
    {
        var originalValue = key.GetValue(name);
        if (value == null)
        {
            if (originalValue == null)
                return false;
            key.DeleteValue(name);
            return true;
        }

        if (value is string && originalValue is string && (string)value == (string)originalValue)
            return false;

        key.SetValue(name, value);
        return true;
    }
}

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