C# winform实现截屏，附代码

namespace Message
{
    partial class Form3
    {
        /// <summary>
        /// Required designer variable.
        /// </summary>
        private System.ComponentModel.IContainer components = null;

        /// <summary>
        /// Clean up any resources being used.
        /// </summary>
        /// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
        protected override void Dispose(bool disposing)
        {
            if (disposing && (components != null))
            {
                components.Dispose();
            }
            base.Dispose(disposing);
        }

        #region Windows Form Designer generated code

        /// <summary>
        /// Required method for Designer support - do not modify
        /// the contents of this method with the code editor.
        /// </summary>
        private void InitializeComponent()
        {
            this.saveFileDialog1 = new System.Windows.Forms.SaveFileDialog();
            this.SuspendLayout();
            // 
            // Form3
            // 
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 12F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(353, 347);
            this.Cursor = System.Windows.Forms.Cursors.Cross;
            this.Name = "Form3";
            this.Text = "Form3";
            this.Load += new System.EventHandler(this.Form3_Load);
            this.MouseUp += new System.Windows.Forms.MouseEventHandler(this.Form3_MouseUp);
            this.MouseDoubleClick += new System.Windows.Forms.MouseEventHandler(this.Form3_DoubleClick);
            this.MouseDown += new System.Windows.Forms.MouseEventHandler(this.Form3_MouseDown);
            this.MouseMove += new System.Windows.Forms.MouseEventHandler(this.Form3_MouseMove);
            this.ResumeLayout(false);

        }

        #endregion

        private System.Windows.Forms.SaveFileDialog saveFileDialog1;
    }
}

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

namespace Message
{
    public partial class Form3 : Form
    {
        private bool down = false;
        private Point firstPoint;
        private Pen p = new Pen(Color.Red);
        private Graphics gra;
        private Rectangle rectangle;//存储用户截取的矩形
        private FormChat f4;
        public Form3(FormChat f4)
        {
            InitializeComponent();
            this.f4 = f4;
        }

        private void Form3_Load(object sender, EventArgs e)
        {
            Image img = new Bitmap(Screen.AllScreens[0].Bounds.Width, Screen.AllScreens[0].Bounds.Height);//创建一个和屏幕同样大小的图像
            Graphics g = Graphics.FromImage(img);//绘制这个图像
            //将屏幕绘制到此图像，第一，二个Point是屏幕要截取的左上角的坐标和绘制到图像的左上角的坐标
            g.CopyFromScreen(new Point(0, 0), new Point(0, 0), Screen.AllScreens[0].Bounds.Size);
            this.BackgroundImage = img;
            this.FormBorderStyle = FormBorderStyle.None;
            this.Bounds = Screen.PrimaryScreen.Bounds;
            gra = this.CreateGraphics();//主要为了用户截取方便
        }
        private void Form3_MouseDown(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left)
            {
                down = true;
                firstPoint = e.Location;
            }
        }

        private void Form3_MouseUp(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left)
            {
                down = false;
            }
            if (e.Button == MouseButtons.Middle)
            {
                this.Close();
            }
        }

        private void Form3_MouseMove(object sender, MouseEventArgs e)
        {
            if (down)
            {
                gra.DrawImage(this.BackgroundImage, 0, 0);
                rectangle = new Rectangle(Math.Min(firstPoint.X, e.X), Math.Min(e.Y, firstPoint.Y), Math.Abs(e.X - firstPoint.X), Math.Abs(e.Y - firstPoint.Y));
                gra.DrawRectangle(p, rectangle);
            }
        }
        private void Form3_DoubleClick(object sender, MouseEventArgs e)
        {
            if (rectangle.Width != 0 && rectangle.Height != 0)
            {
                gra.DrawImage(this.BackgroundImage, 0, 0);
                Image im = new Bitmap(rectangle.Width, rectangle.Height);
                Graphics g = Graphics.FromImage(im);
                g.CopyFromScreen(rectangle.Location, new Point(0, 0), rectangle.Size);
                if (((MouseEventArgs)e).Button == MouseButtons.Left)
                {
                    Clipboard.Clear();
                    Clipboard.SetImage(im);
                    this.f4.Copy();
                    this.Close();
                }
            }
        }
    }
}