How to keep Form1 active?

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Reflection;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();

            FormBorderStyle = FormBorderStyle.None;
            this.WindowState = FormWindowState.Maximized;
        }

        private const int WM_SETREDRAW = 0x000B;

        private void Form1_MouseMove(object sender, MouseEventArgs e)
        {
            Message msgSuspendUpdate = Message.Create(this.Handle, WM_SETREDRAW, IntPtr.Zero,
                    IntPtr.Zero);

            NativeWindow window = NativeWindow.FromHandle(this.Handle);
            window.DefWndProc(ref msgSuspendUpdate);


            IntPtr wparam = new IntPtr(1);
            Message msgResumeUpdate = Message.Create(this.Handle, WM_SETREDRAW, wparam,
                IntPtr.Zero);

            NativeWindow window2 = NativeWindow.FromHandle(this.Handle);
            window2.DefWndProc(ref msgResumeUpdate);
        }
    }
}