Question

Our client (a winforms app) includes a file-browser. I’d like the user to be able to open the selected file using the shell’s default handler. How do I do that? I’ve read that I should use the Win32 API rather than the registry, but I’d prefer a solution that involves only .NET.

Answer 1

EDIT: Newer, simpler answer.

You can indeed just use Process.Start(filename). This is specified in the docs for Process.Start:

Starting a process by specifying its
file name is similar to typing the
information in the Run dialog box of
the Windows Start menu. Therefore, the
file name does not need to represent
an executable file. It can be of any
file type for which the extension has
been associated with an application
installed on the system. For example
the file name can have a .txt
extension if you have associated text
files with an editor, such as Notepad,
or it can have a .doc if you have
associated.doc files with a word
processing tool, such as Microsoft
Word. Similarly, in the same way that
the Run dialog box can accept an
executable file name with or without
the .exe extension, the .exe extension
is optional in the fileName parameter.
For example, you can set the fileName
parameter to either “Notepad.exe” or
“Notepad”.

EDIT: Original, complicated answer:

If you use Process.Start with the file as the “executable” and specify UseShellExecute = true it will just work. For example:

using System;
using System.Diagnostics;

class Test
{
    static void Main()
    {
        ProcessStartInfo psi = new ProcessStartInfo("test.txt");
        psi.UseShellExecute = true;
        Process.Start(psi);
    }
}

That opens test.txt in Notepad.

In fact, UseShellExecute=true is the default, but as it’s definitely required I like to specify it explicitly to make that clearer to the reader.