自定义控件实现Panel中的拖放功能

namespace WindowsFormsApplication5
{
    public partial class ucCloseContact : UserControl
    {
        public ucCloseContact()
        {
            InitializeComponent();
            pictureBox2.MouseMove += pictureBox2_MouseMove;
            pictureBox2.MouseDown += pictureBox2_MouseDown;
            pictureBox2.MouseUp += pictureBox2_MouseUp;
        }
        bool _isMove = false;
        Point _clickPoint;
        
        private void pictureBox2_Paint(object sender, PaintEventArgs e)
        {
            this.BringToFront();//把控件置于顶层
        }
        private void pictureBox2_MouseDown(object sender, MouseEventArgs e)
        {
            //只影响鼠标左键单击
            if (e.Button != MouseButtons.Left)
                return;
            _isMove = true;
            _clickPoint = e.Location;
            //这里还可以改变控件的显示，例如虚化
        }

        private void pictureBox2_MouseMove(object sender, MouseEventArgs e)
        {