c# 实现Label拖动的两种方法

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原文：http://blog.csdn.net/lcawen88/article/details/7942801

在实现Label控件拖动，这里介绍两种有效地方法：

其一，通过调用api，通过消息来实现拖动（需要调用命名空间using System.Runtime.InteropServices;）：

        [DllImport("User32.DLL")]
        public static extern int SendMessage(IntPtr hWnd, uint Msg, int wParam, int lParam);
        [DllImport("User32.DLL")]
        public static extern bool ReleaseCapture();
        public const uint WM_SYSCOMMAND = 0x0112;
        public const int SC_MOVE = 61456;
        public const int HTCAPTION = 2;

        private void label1_MouseDown(object sender, MouseEventArgs e)
        {
            ReleaseCapture();
            SendMessage(((Label)sender).Handle, WM_SYSCOMMAND, SC_MOVE | HTCAPTION, 0);
        }

其二，只是用MouseDown和MouseMove两个事件实现拖动：

        private Point m_lastPoint;
        private Point m_lastMPoint;
        private void label1_MouseDown(object sender, MouseEventArgs e)
        {
            m_lastMPoint = Control.MousePosition;
            m_lastPoint = (sender as Label).Location;
        }

        private void label1_MouseMove(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left)
            {
                label1.Location = new Point(m_lastPoint.X + Control.MousePosition.X - m_lastMPoint.X, m_lastPoint.Y + Control.MousePosition.Y - m_lastMPoint.Y);
            }
        }

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