How do I detect and open custom file extensions automatically and open them with my own exe?

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Hi,
I have created a launcher (console all) that opens my customer file with my exe (let's say the custom file extension is ".abcd"). But to open the file a user has to choose open with option and then choose my exe and say open always. Whereas other applications like VLC or Picasa open defined file extensions automatically. Can anyone help to know the tech behind it and how it works so, I can move on the same path and develop something on my own? TIA.

What I have tried:

Just googled about it. Nothing much.

Posted 22-Sep-24 23:57pm

Faraz Ramish

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Pete O'Hanlon · Accepted Answer · 2024-09-23T00:38:00

I'm going to assume, for the sake of this answer, that you haven't built an installer for your application. If you had, you could register the extension using the installer. Anyway, assuming that you haven't built an installer, you are going to need to modify the registry to perform the association. Be aware that this means that your application will have to run as administrator to actually make the modification. Something like this should help:

C#

public static void RegisterFileExtension(string extension, string applicationPath)
{
    if (!extension.StartsWith("."))
    {
        extension = "." + extension;
    }

    string applicationName = Path.GetFileNameWithoutExtension(applicationPath);
    string keyName = applicationName + "_file";

    SetSubKey(@"Software\Classes\" + extension, "", keyName);

    SetSubKey(@"Software\Classes\" + extension + @"\shell\open\command", "", "\"" + applicationPath + "\" \"%1\"");
}

private static void SetSubKey(string registryPath, string registryKey, value)
{
    using RegistryKey key = Registry.CurrentUser.CreateSubKey(registryPath);
    key.SetValue(registryKey, value);
}

Obviously, the applicationPath is the path to your executable.