using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
namespace WinFormDrag
{
  public partial class Form1 : Form
  {
    //鼠標按下坐標（control控件的相對坐標）
    Point mouseDownPoint = Point.Empty;
    //顯示拖動效果的矩形
    Rectangle rect = Rectangle.Empty;
    //是否正在拖拽
    bool isDrag = false;
    public Form1()
    {
      InitializeComponent();
    }
    private void Form1_Paint(object sender, PaintEventArgs e)
    {
      if (rect != Rectangle.Empty)
      {
        if (isDrag)
        {//畫一個和Control一樣大小的黑框
          e.Graphics.DrawRectangle(Pens.Black, rect);
        }
        else
        {
          e.Graphics.DrawRectangle(new Pen(this.BackColor), rect);
        }
      }
    }
    /// <summary>
    /// 按下鼠標時
    /// </summary>
    /// <param name="sender"></param>
    /// <param name="e"></param>
    private void pb1_MouseDown(object sender, MouseEventArgs e)
    {
      if (e.Button == MouseButtons.Left)
      {
        mouseDownPoint = e.Location;
        //記錄控件的大小
        rect = pb1.Bounds;
      }
    }
    /// <summary>
    /// 移過時
    /// </summary>
    /// <param name="sender"></param>
    /// <param name="e"></param>
    private void pb1_MouseMove(object sender, MouseEventArgs e)
    {
      if (e.Button == MouseButtons.Left)
      {
        isDrag = true;
        //重新設置rect的位置，跟隨鼠標移動
        rect.Location = getPointToForm(new Point(e.Location.X - mouseDownPoint.X, e.Location.Y - mouseDownPoint.Y));
        this.Refresh();
      }
    }
    /// <summary>
    /// 釋放鼠標按鈕時
    /// </summary>
    /// <param name="sender"></param>
    /// <param name="e"></param>
    private void pb1_MouseUp(object sender, MouseEventArgs e)
    {
      if (e.Button == MouseButtons.Left)
      {
        if (isDrag)
        {
          isDrag = false;
          //移動control到放開鼠標的地方
          pb1.Location = rect.Location;
          this.Refresh();
        }
        reset();
      }
    }
    //重置變量
    private void reset()
    {
      mouseDownPoint = Point.Empty;
      rect = Rectangle.Empty;
      isDrag = false;
    }
    //把相對與control控件的坐標，轉(zhuǎn)換成相對于窗體的坐標。
    private Point getPointToForm(Point p)
    {
      return this.PointToClient(pb1.PointToScreen(p));
    }
  }
}