如果用HttpWebRequest和HttpWebResponse從服務器取圖片，會觸發圖片變化。於是想到從IE緩存讀取圖片

參考https://www.cnblogs.com/yelaiju/archive/2010/10/01/1839860.html和https://blog.csdn.net/annkie/article/details/6065521和http://www.mamicode.com/info-detail-370382.html

代碼如下：

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
 
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;

namespace Common
{
    class Program
    {//從ＩＥ緩存復制圖片到Ｄ盤
        static void Main(string[] args)
        {            
            System.Diagnostics.Process.Start(" http://www.baidu.com ");
            System.Threading.Thread.Sleep(
 
2000);           
            //打開ＩＥ緩存目錄
            Process.Start(Environment.GetFolderPath(Environment.SpecialFolder.InternetCache));            
            IECache i = new IECache();
            //在網頁上找到百度logo圖片的url寫在下面
            string b = i.GetPathForCachedFile("https://www.baidu.com/img/bd_logo1.png");
            Console.WriteLine(b);
            
 
//從緩存中將bd_logo1.png拷貝到Ｄ盤下
            File.Copy(b, @"d:\bd_logo1.png", true);
            Console.WriteLine("現在打開Ｄ盤目錄看看bd_logo1.png吧");
            Console.ReadKey();


        }
        public class IECache
        {
            [DllImport("Wininet.dll", SetLastError = true, CharSet = CharSet.Auto)]
            public static extern Boolean GetUrlCacheEntryInfo(String lpxaUrlName, IntPtr lpCacheEntryInfo, ref int lpdwCacheEntryInfoBufferSize);
            const int ERROR_FILE_NOT_FOUND = 0x2;
            struct LPINTERNET_CACHE_ENTRY_INFO
            {
                public int dwStructSize;
                IntPtr lpszSourceUrlName;
                public IntPtr lpszLocalFileName;
               // int CacheEntryType;
               // int dwUseCount;
               // int dwHitRate;
                //int dwSizeLow;
               // int dwSizeHigh;

                //System.Runtime.InteropServices.ComTypes.FILETIME LastModifiedTime;
                //System.Runtime.InteropServices.ComTypes.FILETIME Expiretime;
               // System.Runtime.InteropServices.ComTypes.FILETIME LastAccessTime;
                //System.Runtime.InteropServices.ComTypes.FILETIME LastSyncTime;
                //IntPtr lpHeaderInfo;
                //readonly int dwheaderInfoSize;
                //IntPtr lpszFileExtension;
                //int dwEemptDelta;
            }
            // 返回 指定URL文件的緩存在本地文件系統中的路徑
            public string GetPathForCachedFile(string fileUrl)
            {
                int cacheEntryInfoBufferSize = 0;
                IntPtr cacheEntryInfoBuffer = IntPtr.Zero;
                int lastError; Boolean result;
                try
                {
                    result = GetUrlCacheEntryInfo(fileUrl, IntPtr.Zero, ref cacheEntryInfoBufferSize);
                    lastError = Marshal.GetLastWin32Error();
                    if (result == false)
                    {
                        if (lastError == ERROR_FILE_NOT_FOUND)
                            return null;
                    }
                    cacheEntryInfoBuffer = Marshal.AllocHGlobal(cacheEntryInfoBufferSize);
                    result = GetUrlCacheEntryInfo(fileUrl, cacheEntryInfoBuffer, ref cacheEntryInfoBufferSize);
                    lastError = Marshal.GetLastWin32Error();
                    if (result == true)
                    {
                        Object strObj = Marshal.PtrToStructure(cacheEntryInfoBuffer, typeof(LPINTERNET_CACHE_ENTRY_INFO));
                        LPINTERNET_CACHE_ENTRY_INFO internetCacheEntry = (LPINTERNET_CACHE_ENTRY_INFO)strObj;
                        String localFileName = Marshal.PtrToStringAuto(internetCacheEntry.lpszLocalFileName); return localFileName;
                    }
                    else
                        return null;// file not found
                }
                finally
                {
                    if (!cacheEntryInfoBuffer.Equals(IntPtr.Zero))
                        Marshal.FreeHGlobal(cacheEntryInfoBuffer);
                }
            }
        }
    }
}

Ｃ#從IE緩存讀取圖片