Question

I have a need to launch multiple browser instances / tabs in succession but using Process.Start(url) I am finding that not every URL is launched.

    for (int i = 0; i < n; i++)
    {
        var p = Process.Start("http://localhost/#" + i.ToString());
    }

For any value n > 1 I find that only the last URL is opened in the browser (I’m testing with IE as the default browser). If I add a Thread.Sleep(1000) after Process.Start then I see a variety of behavior: sometimes all n are created; sometimes a subset.

The following does work as expected, but assumes IE (would rather use the default browser) and launches n browser instances rather than n tabs:

    for (int i = 0; i < n; i++)
    {
        var p = Process.Start("iexplore.exe", "http://localhost/#" + i.ToString());
    }

I would prefer to get it working with the default browser behavior, but need it to be deterministic.

Answer 1

Ended up with the following, still not ideal (launches multiple browser windows), incorporating the command-line arg parsing solution Split string containing command-line parameters into string[] in C#

const int n = 3;
static void Main(string[] args)
{
    for (int i = 0; i < n; i++)
    {
        var start = GetDefaultBrowserStartInfo("http");
        start.Arguments += string.Format(" http://localhost/#{0}", i);

        var p = Process.Start(start);
    }
}

static ProcessStartInfo GetDefaultBrowserStartInfo(string scheme)
{
    string command = null;
    using (var key = Registry.ClassesRoot.OpenSubKey(string.Format(@"{0}\shell\open\command", scheme)))
    {
        command = (string)key.GetValue("");
    }

    string[] parsed = CommandLineToArgs(command);
    return new ProcessStartInfo
    {
        FileName = parsed[0],
        Arguments = string.Join(" ", parsed.Skip(1).ToArray()),
    };
}

[DllImport("shell32.dll", SetLastError = true)]
static extern IntPtr CommandLineToArgvW(
    [MarshalAs(UnmanagedType.LPWStr)] string lpCmdLine, out int pNumArgs);

static string[] CommandLineToArgs(string commandLine)
{
    int argc;
    var argv = CommandLineToArgvW(commandLine, out argc);
    if (argv == IntPtr.Zero)
        throw new System.ComponentModel.Win32Exception();
    try
    {
        var args = new string[argc];
        for (var i = 0; i < args.Length; i++)
        {
            var p = Marshal.ReadIntPtr(argv, i * IntPtr.Size);
            args[i] = Marshal.PtrToStringUni(p);
        }

        return args;
    }
    finally
    {
        Marshal.FreeHGlobal(argv);
    }
}

}