C# Winform实现截图工具的示例代码

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 OCR
{
    public partial class ScreenBody : Form
    {
        public static Image myImage;


        private Graphics MainPainter;   //主画面
        private Pen pen;                //画笔
        private bool isDowned;          //判断鼠标是否按下 
        private bool RectReady;         //矩形是否绘制完成 
        private Image baseImage;        //基本图形(原来的画面) 
        private Rectangle Rect;         //就是要保存的矩形 
        private Point downPoint;        //鼠标按下的点 
        int tmpx;
        int tmpy;

        public ScreenBody()
        {
            InitializeComponent();
        }

        private void ScreenBody_Load(object sender, EventArgs e)
        {
            try
            {
                this.WindowState = FormWindowState.Maximized;
                MainPainter = this.CreateGraphics();
                pen = new Pen(Brushes.Blue);
                isDowned = false;
                baseImage = this.BackgroundImage;
                Rect = new Rectangle();
                RectReady = false;
            }
            catch (Exception ex)
            {
                log4netHelper.Error("---报错方法--ScreenBody_Load");
                log4netHelper.Error(ex.Message);
                log4netHelper.Error(ex.StackTrace);
                log4netHelper.Error("---end---");
            }

        }

        private void ScreenBody_MouseDown(object sender, MouseEventArgs e)
        {
            try
            {
                if (e.Button == MouseButtons.Left)
                {
                    isDowned = true;

                    if (RectReady == false)
                    {
                        Rect.X = e.X;
                        Rect.Y = e.Y;
                        downPoint = new Point(e.X, e.Y);
                    }
                    if (RectReady == true)
                    {
                        tmpx = e.X;
                        tmpy = e.Y;
                    }
                }
                if (e.Button == MouseButtons.Right)
                {
                    this.Close();
                    return;
                }
            }
            catch (Exception ex)
            {
                log4netHelper.Error("---报错方法--ScreenBody_MouseDown");
                log4netHelper.Error(ex.Message);
                log4netHelper.Error(ex.StackTrace);
                log4netHelper.Error("---end---");
            }

        }

        private void ScreenBody_MouseUp(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left)
            {
                isDowned = false;
                RectReady = true;
            }
        }

        private void ScreenBody_MouseMove(object sender, MouseEventArgs e)
        {
            try
            {
                if (RectReady == false)
                {
                    if (isDowned == true)
                    {
                        Image New = DrawScreen((Image)baseImage.Clone(), e.X, e.Y);
                        MainPainter.DrawImage(New, 0, 0);
                        New.Dispose();
                    }
                }
                if (RectReady == true)
                {
                    if (Rect.Contains(e.X, e.Y))
                    {
                        this.Cursor = Cursors.Hand;
                        if (isDowned == true)
                        {
                            //和上一次的位置比较获取偏移量 
                            Rect.X = Rect.X + e.X - tmpx;
                            Rect.Y = Rect.Y + e.Y - tmpy;
                            //记录现在的位置 
                            tmpx = e.X;
                            tmpy = e.Y;
                            MoveRect((Image)baseImage.Clone(), Rect);
                        }
                    }
                    else
                    {
                        this.Cursor = Cursors.Arrow;
                    }
                }
            }
            catch (Exception ex)
            {
                log4netHelper.Error("---报错方法--ScreenBody_MouseMove");
                log4netHelper.Error(ex.Message);
                log4netHelper.Error(ex.StackTrace);
                log4netHelper.Error("---end---");
            }

        }


        //画屏幕
        private Image DrawScreen(Image back, int Mouse_x, int Mouse_y)
        {
            try
            {
                Graphics Painter = Graphics.FromImage(back);
                DrawRect(Painter, Mouse_x, Mouse_y);
                return back;
            }
            catch (Exception ex)
            {
                log4netHelper.Error("---报错方法--DrawScreen");
                log4netHelper.Error(ex.Message);
                log4netHelper.Error(ex.StackTrace);
                log4netHelper.Error("---end---");
                return null;
            }

        }
        //画矩形
        private void DrawRect(Graphics Painter, int Mouse_x, int Mouse_y)
        {
            int width = 0;
            int heigth = 0;
            try
            {
                if (Mouse_y < Rect.Y)
                {
                    Rect.Y = Mouse_y;
                    heigth = downPoint.Y - Mouse_y;
                }
                else
                {
                    heigth = Mouse_y - downPoint.Y;
                }
                if (Mouse_x < Rect.X)
                {
                    Rect.X = Mouse_x;
                    width = downPoint.X - Mouse_x;
                }
                else
                {
                    width = Mouse_x - downPoint.X;
                }
            }
            catch (Exception ex)
            {
                log4netHelper.Error("---报错方法--DrawRect");
                log4netHelper.Error(ex.Message);
                log4netHelper.Error(ex.StackTrace);
                log4netHelper.Error("---end---");
            }
            finally
            {
                Rect.Size = new Size(width, heigth);
                Painter.DrawRectangle(pen, Rect);
            }
        }

        //移动矩形
        private void MoveRect(Image image, Rectangle Rect)
        {
            try
            {
                Graphics Painter = Graphics.FromImage(image);
                Painter.DrawRectangle(pen, Rect.X, Rect.Y, Rect.Width, Rect.Height);
                MainPainter.DrawImage(image, 0, 0);
                image.Dispose();
            }
            catch (Exception ex)
            {
                log4netHelper.Error("---报错方法--MoveRect");
                log4netHelper.Error(ex.Message);
                log4netHelper.Error(ex.StackTrace);
                log4netHelper.Error("---end---");
            }

        }

        private void ScreenBody_MouseDoubleClick(object sender, MouseEventArgs e)
        {
            try
            {
                Image memory = new Bitmap(Rect.Width, Rect.Height);
                Graphics g = Graphics.FromImage(memory);
                g.CopyFromScreen(Rect.X + 1, Rect.Y + 1, 0, 0, new Size(Rect.Size.Width - 2, Rect.Size.Height - 2));
                myImage = memory;
                this.Close();
                this.Dispose();
            }
            catch (Exception ex)
            {
                log4netHelper.Error("---报错方法--ScreenBody_MouseDoubleClick");
                log4netHelper.Error(ex.Message);
                log4netHelper.Error(ex.StackTrace);
                log4netHelper.Error("---end---");
            }

        }
    }
}

using System;
using System.Runtime.InteropServices;
using System.Windows.Forms;

namespace OCR
{
    public class HotKey
    {
        //如果函数执行成功，返回值不为0。
        //如果函数执行失败，返回值为0。要得到扩展错误信息，调用GetLastError。
        [DllImport("user32.dll", SetLastError = true)]
        public static extern bool RegisterHotKey(
            IntPtr hWnd,                //要定义热键的窗口的句柄
            int id,                     //定义热键ID（不能与其它ID重复）           
            KeyModifiers fsModifiers,   //标识热键是否在按Alt、Ctrl、Shift、Windows等键时才会生效
            Keys vk                     //定义热键的内容
            );

        [DllImport("user32.dll", SetLastError = true)]
        public static extern bool UnregisterHotKey(
            IntPtr hWnd,                //要取消热键的窗口的句柄
            int id                      //要取消热键的ID
            );

        //定义了辅助键的名称（将数字转变为字符以便于记忆，也可去除此枚举而直接使用数值）
        [Flags()]
        public enum KeyModifiers
        {
            None = 0,
            Alt = 1,
            Ctrl = 2,
            Shift = 4,
            WindowsKey = 8
        }

    }
}