代码：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.IO;
namespace TestKeyPress
{
    public partial class Form2 : Form
    {
        public Form2()
        {
            InitializeComponent();
        }
    
        private void textBox1_DragEnter(object sender, DragEventArgs e)
        {
            e.Effect = DragDropEffects.Copy;
        }
        private void textBox1_DragDrop(object sender, DragEventArgs e)
        {
         //DataFormats.FileDrop确定你拖动过去的是文件回或者文件夹
            if (e.Data.GetDataPresent(DataFormats.FileDrop))
            {
                string realpath = ((System.Array)e.Data.GetData(DataFormats.FileDrop)).GetValue(0).ToString();
                //从拖动数据里得到路径
                //MessageBox.Show(realpath);测试路径
                string p = Path.GetExtension(realpath);
                //MessageBox.Show(p);测试路径
                if (p == ".jpg")
                {
                    //StreamReader sr = new StreamReader(realpath);读取方式，放弃使用
                    Image im = Image.FromFile(realpath);
                    int h = im.Height;
                    int w = im.Width;
                    this.pictureBox1.Height = h;
                    this.pictureBox1.Width = w;
                    this.pictureBox1.BackgroundImageLayout = ImageLayout.Stretch;
                    this.pictureBox1.BackgroundImage = im;
                    //将读取到的图片放到picturebox里
                    //this.pictureBox1.Location = new Point(130 - pictureBox1.Width, 85 - pictureBox1.Height);
                    Point pnl = new Point(this.p