C# 获取exe、dll中的图标，支持获取256x256分辨率

在网上找过许多文章，都没有成功获取过大图标，只能获取最大32x32。最后自己尝试了相关的windows api，终于找到一个可用的。

主要用到的C++的PrivateExtractIcons函数，具体说明请看：PrivateExtractIcons function

该函数原文有个说明可能需要注意一下：[This function is not intended for general use. It may be altered or unavailable in subsequent versions of Windows.]

 UINT WINAPI PrivateExtractIcons(
   _In_      LPCTSTR lpszFile,
   _In_      int     nIconIndex,
   _In_      int     cxIcon,
   _In_      int     cyIcon,
   _Out_opt_ HICON   *phicon,
   _Out_opt_ UINT    *piconid,
   _In_      UINT    nIcons,
   _In_      UINT    flags
 );

C#使用DLL import进行引用。

 [DllImport("User32.dll")]
 public static extern int PrivateExtractIcons(
     string lpszFile, //文件名可以是exe,dll,ico,cur,ani,bmp
     int nIconIndex,  //从第几个图标开始获取
     int cxIcon,      //获取图标的尺寸x
     int cyIcon,      //获取图标的尺寸y
     IntPtr[] phicon, //获取到的图标指针数组
     int[] piconid,   //图标对应的资源编号
     int nIcons,      //指定获取的图标数量，仅当文件类型为.exe 和 .dll时候可用
     int flags        //标志，默认0就可以，具体可以看LoadImage函数
 );

说明：如果想要获取的图标尺寸为256x256，而实际资源文件中的图标尺寸小于256x256的话，则会获取存在的最高分标率，色彩数最丰富的的图标，并拉伸。

具体代码如下

 using System;
 using System.Collections.Generic;
 using System.Drawing;
 using System.Drawing.Imaging;
 using System.IO;
 using System.Linq;
 using System.Runtime.InteropServices;
 using System.Text;
 using System.Threading.Tasks;

 namespace TryGetExeLargeIcon
 {
     class Program
     {
         [STAThread]
         static void Main(string[] args)
         {
             //选择文件对话框
             var opfd = new System.Windows.Forms.OpenFileDialog { Filter = "资源文件|*.exe;*.dll" };
             if (opfd.ShowDialog() != System.Windows.Forms.DialogResult.OK) return;
             var file = opfd.FileName;

             //指定存放图标的文件夹
             const string folderToSave = "D:\\temp\\";
             if (!Directory.Exists(folderToSave)) Directory.CreateDirectory(folderToSave);

             //选中文件中的图标总数
             var iconTotalCount = PrivateExtractIcons(file, , , , null, null, , );

             //用于接收获取到的图标指针
             IntPtr[] hIcons = new IntPtr[iconTotalCount];
             //对应的图标id
             int[] ids = new int[iconTotalCount];
             //成功获取到的图标个数
             var successCount = PrivateExtractIcons(file, , , , hIcons, ids, iconTotalCount, );

             //遍历并保存图标
             for (var i = ; i < successCount; i++)
             {
                 //指针为空，跳过
                 if (hIcons[i] == IntPtr.Zero) continue;

                 using (var ico = Icon.FromHandle(hIcons[i]))
                 {
                     using (var myIcon = ico.ToBitmap())
                     {
                         myIcon.Save(folderToSave + ids[i].ToString("") + ".png", ImageFormat.Png);
                     }
                 }
                 //内存回收
                 DestroyIcon(hIcons[i]);
             }
         }

         //details: https://msdn.microsoft.com/en-us/library/windows/desktop/ms648075(v=vs.85).aspx
         //Creates an array of handles to icons that are extracted from a specified file.
         //This function extracts from executable (.exe), DLL (.dll), icon (.ico), cursor (.cur), animated cursor (.ani), and bitmap (.bmp) files.
         //Extractions from Windows 3.x 16-bit executables (.exe or .dll) are also supported.
         [DllImport("User32.dll")]
         public static extern int PrivateExtractIcons(
             string lpszFile, //file name
             int nIconIndex,  //The zero-based index of the first icon to extract.
             int cxIcon,      //The horizontal icon size wanted.
             int cyIcon,      //The vertical icon size wanted.
             IntPtr[] phicon, //(out) A pointer to the returned array of icon handles.
             int[] piconid,   //(out) A pointer to a returned resource identifier.
             int nIcons,      //The number of icons to extract from the file. Only valid when *.exe and *.dll
             int flags        //Specifies flags that control this function.
         );

         //details:https://msdn.microsoft.com/en-us/library/windows/desktop/ms648063(v=vs.85).aspx
         //Destroys an icon and frees any memory the icon occupied.
         [DllImport("User32.dll")]
         public static extern bool DestroyIcon(
             IntPtr hIcon //A handle to the icon to be destroyed. The icon must not be in use.
         );
     }
 }