C#如何通过文件流前2个字节确定文件类型

1、 打开VS，选择Visual C#模板创建WinForm应用程序。输入一个自己满意的解决方案名称，并指定其位置，点击确认按钮进入代码编写界面。

2、在Form1.Designer.cs页面中找到 partial class Form1{……}整段代码，即图中框选区域代码，用下面代码进行替换。

 partial class Form1

    {
        /// <summary>
        /// 必需的设计器变量。
        /// </summary>
        private System.ComponentModel.IContainer components = null;

        /// <summary>

        /// 清理所有正在使用的资源。
        /// </summary>
        /// <param name="disposing">如果应释放托管资源，为 true；否则为 false。</param>
        protected override void Dispose(bool disposing)
        {
            if (disposing && (components != null))
            {
                components.Dispose();
            }
            base.Dispose(disposing);
        }

        #region Windows 窗体设计器生成的代码

        /// <summary>

        /// 设计器支持所需的方法 - 不要
        /// 使用代码编辑器修改此方法的内容。
        /// </summary>
        private void InitializeComponent()
        {
            this.label1 = new System.Windows.Forms.Label();
            this.SuspendLayout();
            //
            // label1
            //
            this.label1.AutoSize = true;
            this.label1.Location = new System.Drawing.Point(103, 83);
            this.label1.Name = "label1";
            this.label1.Size = new System.Drawing.Size(41, 12);
            this.label1.TabIndex = 0;
            this.label1.Text = "label1";
            //
            // Form1
            //
            this.AllowDrop = true;
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 12F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(239, 198);
            this.Controls.Add(this.label1);
            this.Name = "Form1";
            this.Text = "Form1";
            this.DragDrop += new System.Windows.Forms.DragEventHandler(this.Form1_DragDrop);
            this.DragEnter += new System.Windows.Forms.DragEventHandler(this.Form1_DragEnter);
            this.ResumeLayout(false);
            this.PerformLayout();

        }

        #endregion

        private System.Windows.Forms.Label label1;

    }

3、在Form1页面中找到public partial class Form1 : Form{……}整段代码，即图中框选区域代码，用下面代码进行替换。

    public partial class Form1 : Form

    {
        public Form1()
        {
            InitializeComponent();
        }
        private void Form1_DragEnter(object sender, DragEventArgs e)
        {
            if (e.Data.GetDataPresent(DataFormats.FileDrop))
                e.Effect = DragDropEffects.All;
            else
                e.Effect = DragDropEffects.None;
        }
        private void Form1_DragDrop(object sender, DragEventArgs e)
        {
            string[] s = (string[])e.Data.GetData(DataFormats.FileDrop, false);
            string fileName = s[0];

            System.IO.FileStream fs = new System.IO.FileStream(fileName, System.IO.FileMode.Open, System.IO.FileAccess.Read);

            byte[] bs = new byte[2];
            fs.Read(bs, 0, 2);
            fs.Close();

            int n = bs[0] * 256 + bs[1];

            switch (n)
            {
                case 255*256+216:
                    this.label1.Text = ".jpg";
                    break ;
                case 208 * 256 + 207:
                    this.label1.Text = ".doc .xls .ppt .wps";
                    break;
                case 80 * 256 + 75:
                    this.label1.Text = ".docx .pptx .xlsx .zip";
                    break;
                case 82 * 256 + 97:
                    this.label1.Text = ".rar";
                    break;
                case 77 * 256 + 90:
                    this.label1.Text = ".exe .dll";
                    break;
                case 9552:
                    this.label1.Text = ".pdf";
                    break;
                case 71 * 256 + 73:
                    this.label1.Text = ".gif";
                    break;
                case 137 * 256 + 80:
                    this.label1.Text = ".png";
                    break;
                case 66 * 256 + 77:
                    this.label1.Text = ".bmp";
                    break;
                case 56 * 256 + 66:
                    this.label1.Text = ".psd";
                    break;
                case 60 * 256 + 63:
                    this.label1.Text = ".xml";
                    break;
                case 60 * 256 + 33:
                    this.label1.Text = ".htm  .html";
                    break;
                case 64 * 256 + 101:
                    this.label1.Text = ".bat";
                    break;
                default :
                    this.label1.Text = n.ToString();
                    break;
            }
        }
    }

4、编译代码，生成解决方案。

5、编译成功后，按F5执行，拖动一个文件放置到软件窗口中，窗口将显示文件类型，如果文件类型不在当前代码统计中，则会显示前2个字节数值，一般可以将其添加到软件中。