How to control which version of Mathematica .NET/Link uses

Question

I have three versions of Mathematica installed: 7.0.1, 11.0.1 and 11.1.1 but my test .NET/Link application will only use version 7. In Visual Studio I have referenced the Wolfram.NETLink.dll and included the ml32i4.dll from version 11.1.1 but still the MathKernel uses version 7. Is there some way I can control which version MathKernel uses?

using System;
using System.Linq;
using System.Windows.Forms;
using Wolfram.NETLink;

namespace NetLink_test_application
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            MathKernel k = null;
            try
            {
                k = CreateKernel();
                k.Compute("Export[\"C:\\\\Users\\\\chrisd\\\\Documents\\\\test.txt\",$VersionNumber]");
                if (k.Messages.Any())
                {
                    string allMessages = "";
                    foreach (string msg in k.Messages)
                        allMessages += msg + Environment.NewLine;
                    foreach (string msg in k.PrintOutput)
                        allMessages += msg + Environment.NewLine;
                    MessageBox.Show(allMessages, "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
                }
                //return k.Result.ToString();
            }
            catch
            {
                MessageBox.Show("Error connecting to Mathematica - please lose all open Mathematica windows, and then try again",
                                "Mathematica Error", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
            }
            finally
            {
                if (k != null)
                    k.Dispose();
            }
            //return "";
        }

        public static MathKernel CreateKernel()
        {
            MathKernel mathKernel = new MathKernel
            {
                AutoCloseLink = true,
                CaptureGraphics = true,
                CaptureMessages = true,
                CapturePrint = true,
                GraphicsFormat = "Metafile",
                GraphicsHeight = 0,
                GraphicsResolution = 80,
                GraphicsWidth = 0,
                HandleEvents = true,
                Input = null,
                Link = null,
                LinkArguments = null,
                PageWidth = 0,
                ResultFormat = MathKernel.ResultFormatType.OutputForm,
                UseFrontEnd = true
            };
            return mathKernel;
        }
    }
}

The program above runs the Mathematica code

Export["C:\\Users\\chrisd\\Documents\\test.txt", $VersionNumber]

producing a text file containing 7. confirming the version used.

Details of the .NET/Link reference and included ml32i4.dll

Solution courtesy of Szabolcs

Specify the link in the CreateKernel method as shown below:-

        public static MathKernel CreateKernel()
        {
            string mlArgs = "-linkmode launch -linkname \"C:\\\\Program Files\\\\Wolfram Research\\\\Mathematica\\\\11.1\\\\MathKernel.exe\"";
            IKernelLink ml = MathLinkFactory.CreateKernelLink(mlArgs);

            MathKernel mathKernel = new MathKernel
            {
                AutoCloseLink = true,
                CaptureGraphics = true,
                CaptureMessages = true,
                CapturePrint = true,
                GraphicsFormat = "Metafile",
                GraphicsHeight = 0,
                GraphicsResolution = 80,
                GraphicsWidth = 0,
                HandleEvents = true,
                Input = null,
                Link = ml,
                LinkArguments = null,
                PageWidth = 0,
                ResultFormat = MathKernel.ResultFormatType.OutputForm,
                UseFrontEnd = true
            };
            return mathKernel;
        }

Answer 1

I do not know any C#, but this seems to be answered in the documentation. Since I am reading the local copy, not an online version, I cannot post links. Here are screenshots instead:

Thus if you need to specify the location of the Mathematica kernel to use, pass the appropriate string to CreateKernelLink(). This is not simply the path to the kernel, but a set of MathLink arguments. See the example in the documentation.

You can create a MathKernel object from an IKernelLink.