C# Winform中WndProc 函式作用：

主要用在攔截並處理系統訊息和自定義訊息

比如:
windows程式會產生很多訊息，比如你單擊滑鼠，移動視窗都會產生訊息。這個函式就是預設的訊息處理函式。你可以過載這個函式來制定自己的訊息處理流程.

在Winform程式中，可以重寫WndProc函式，來捕捉所有發生的視窗訊息。

這樣，我們就可以"篡改"傳入的訊息，而人為的讓視窗改變行為。

我們用C#實現檢測U盤插拔的功能，是用重寫C# WndProc函式來做到的。 

簡單測試程式碼：

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;
using System.IO;  //新增IO名稱空間

namespace CheckUdisk
{
    public partial class Form1 : Form
    {

        //定義常量
        public const int WM_DEVICECHANGE = 0x219;
        public const int DBT_DEVICEARRIVAL = 0x8000;
        public const int DBT_CONFIGCHANGECANCELED = 0x0019;
        public const int DBT_CONFIGCHANGED = 0x0018;
        public const int DBT_CUSTOMEVENT = 0x8006;           
        public const int DBT_DEVICEQUERYREMOVE = 0x8001;
        public const int DBT_DEVICEQUERYREMOVEFAILED = 0x8002;
        public const int DBT_DEVICEREMOVECOMPLETE = 0x8004;
        public const int DBT_DEVICEREMOVEPENDING = 0x8003;
        public const int DBT_DEVICETYPESPECIFIC = 0x8005;
        public const int DBT_DEVNODES_CHANGED = 0x0007;
        public const int DBT_QUERYCHANGECONFIG = 0x0017;
        public const int DBT_USERDEFINED = 0xFFFF;



        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }

        protected override void WndProc(ref Message m)
        {

            try
            {
                if (m.Msg == WM_DEVICECHANGE)
                {
                    switch (m.WParam.ToInt32())
                    {
                        case WM_DEVICECHANGE:
                            break;
                        case DBT_DEVICEARRIVAL:
                            DriveInfo[] s = DriveInfo.GetDrives();
                            foreach (DriveInfo drive in s)
                            {
                                if (drive.DriveType == DriveType.Removable)
                                {
                                    this.richTextBox1.AppendText("U盤已插入，碟符是" + drive.Name.ToString() + "\r\n");
                                    break;
                                }
                            }
                            break;
                        case DBT_CONFIGCHANGECANCELED:
                            MessageBox.Show("2");
                            break;
                        case DBT_CONFIGCHANGED:
                            MessageBox.Show("3");
                            break;
                        case DBT_CUSTOMEVENT:
                            MessageBox.Show("4");
                            break;
                        case DBT_DEVICEQUERYREMOVE:
                            MessageBox.Show("5");
                            break;
                        case DBT_DEVICEQUERYREMOVEFAILED:
                            MessageBox.Show("6");
                            break;
                        case DBT_DEVICEREMOVECOMPLETE:
                            this.richTextBox1.AppendText("U盤已解除安裝");
                            break;
                        case DBT_DEVICEREMOVEPENDING:
                            MessageBox.Show("7");
                            break;
                        case DBT_DEVICETYPESPECIFIC:
                            MessageBox.Show("8");
                            break;
                        case DBT_DEVNODES_CHANGED:
                            MessageBox.Show("9");
                            break;
                        case DBT_QUERYCHANGECONFIG:
                            MessageBox.Show("10");
                            break;
                        case DBT_USERDEFINED:
                            MessageBox.Show("11");
                            break;
                        default:
                            break;
                    }
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }

            base.WndProc(ref m);
        }
    }
}