C#如何实现拖动按钮时不触发Click事件

如题，做了一个在运行时可拖动的按钮，可是每次一拖动就会触发Click事件，怎样才能实现只拖动按钮而不触发Click事件，Click事件是必要的，不可省

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

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        private Point buttonlocation;

        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            MessageBox.Show("button1");
        }

        private void button1_MouseUp(object sender, MouseEventArgs e)
        {
            buttonlocation = e.Location;            
        }

        private void button1_MouseMove(object sender, MouseEventArgs e)
        {
            if (e.Button == System.Windows.Forms.MouseButtons.Left)
            {
                this.button1.Click -= button1_Click;
                this.button1.Location = new Point(this.button1.Left + (e.X - buttonlocation.X), this.button1.Top + (e.Y - buttonlocation.Y));
            }
        }

        private void button1_MouseDown(object sender, MouseEventArgs e)
        {
            buttonlocation = e.Location;
            this.button1.Click -= button1_Click;
            this.button1.Click += button1_Click;
        }
    }
}

应该使用onclick,而不是onmousedown