在C#中如何使用GetOpenFileName函数多选文件

在前面的文章中，https://www.cnblogs.com/zhaotianff/p/13999133.html

介绍了Windows的通用对话框，其中就包括 了打开 文件 对话框。

正常情况下，在C#中需要 浏览文件 ，直接 调用 System.Windows.Forms.OpenFileDialog或Microsoft.Win32.OpenFileDialog类即可 ，但在某些特殊情况下，无法调用这两个类，所以就需要用到API函数GetOpenFileName来浏览文件。

声明OpenFileName结构体

[StructLayout(LayoutKind.Sequential, CharSet=CharSet.Auto)]
public struct OpenFileName
{
    public int lStructSize;
    public IntPtr hwndOwner;
    public IntPtr hInstance;
    public string lpstrFilter;
    public string lpstrCustomFilter;
    public int nMaxCustFilter;
    public int nFilterIndex;
    public string lpstrFile;
    public int nMaxFile;
    public string lpstrFileTitle;
    public int nMaxFileTitle;
    public string lpstrInitialDir;
    public string lpstrTitle;
    public int Flags;
    public short nFileOffset;
    public short nFileExtension;
    public string lpstrDefExt;
    public IntPtr lCustData;
    public IntPtr lpfnHook;
    public string lpTemplateName;
    public IntPtr pvReserved;
    public int dwReserved;
    public int flagsEx;
}

常量 

public const int OFN_READONLY = 0x1;
        public const int OFN_OVERWRITEPROMPT = 0x2;
        public const int OFN_HIDEREADONLY = 0x4;
        public const int OFN_NOCHANGEDIR = 0x8;
        public const int OFN_SHOWHELP = 0x10;
        public const int OFN_ENABLEHOOK = 0x20;
        public const int OFN_ENABLETEMPLATE = 0x40;
        public const int OFN_ENABLETEMPLATEHANDLE = 0x80;
        public const int OFN_NOVALIDATE = 0x100;
        public const int OFN_ALLOWMULTISELECT = 0x200;
        public const int OFN_EXTENSIONDIFFERENT = 0x400;
        public const int OFN_PATHMUSTEXIST = 0x800;
        public const int OFN_FILEMUSTEXIST = 0x1000;
        public const int OFN_CREATEPROMPT = 0x2000;
        public const int OFN_SHAREAWARE = 0x4000;
        public const int OFN_NOREADONLYRETURN = 0x8000;
        public const int OFN_NOTESTFILECREATE = 0x10000;
        public const int OFN_NONETWORKBUTTON = 0x20000;
        public const int OFN_NOLONGNAMES = 0x40000;
        public const int OFN_EXPLORER = 0x80000;
        public const int OFN_NODEREFERENCELINKS = 0x100000;
        public const int OFN_LONGNAMES = 0x200000;
        public const int OFN_ENABLEINCLUDENOTIFY = 0x400000;
        public const int OFN_ENABLESIZING = 0x800000;
        public const int OFN_DONTADDTORECENT = 0x2000000;
        public const int OFN_FORCESHOWHIDDEN = 0x10000000;
        public const int OFN_EX_NOPLACESBAR = 0x1;
        public const int OFN_SHAREFALLTHROUGH = 2;
        public const int OFN_SHARENOWARN = 1;
        public const int OFN_SHAREWARN = 0;

API函数签名 

  [DllImport("comdlg32.dll", SetLastError = true, CharSet = CharSet.Auto)]
        static extern bool GetOpenFileName([In, Out] OpenFileName ofn);

调用示例：

 static List<string> BrowseMultiFile(string filter)
        {
            int size = 1024;
            List<string> list = new List<string>();
            //多选文件是传出一个指针，这里需要提前分配空间
            //如果是单选文件，使用已经分配大小的StringBuilder或string
            IntPtr filePtr = Marshal.AllocHGlobal(size);

            //清空分配的内存区域
            for (int i = 0; i < size; i++)
            {
                Marshal.WriteByte(filePtr, i, 0);
            }

            OpenFileName openFileName = new OpenFileName();
            openFileName.lStructSize = Marshal.SizeOf(openFileName);
            openFileName.lpstrFilter = filter;
            openFileName.filePtr = filePtr;
            openFileName.nMaxFile = size;
            openFileName.lpstrFileTitle = new string(new char[64]);
            openFileName.nMaxFileTitle = 64;
            openFileName.lpstrInitialDir = Environment.GetFolderPath(Environment.SpecialFolder.Desktop);
            openFileName.lpstrFileTitle = "浏览文件";
            openFileName.lpstrDefExt = "*.*";
            openFileName.Flags = WinAPI.OFN_EXPLORER | WinAPI.OFN_FILEMUSTEXIST | WinAPI.OFN_PATHMUSTEXIST | WinAPI.OFN_ALLOWMULTISELECT| WinAPI.OFN_NOCHANGEDIR;
            if(WinAPI.GetOpenFileName(openFileName))
            {
                var file = Marshal.PtrToStringAuto(openFileName.filePtr);
                while(!string.IsNullOrEmpty(file))
                {
                    list.Add(file);
                    //转换为地址
                    long filePointer = (long)openFileName.filePtr;
                    //偏移
                    filePointer += file.Length * Marshal.SystemDefaultCharSize + Marshal.SystemDefaultCharSize;
                    openFileName.filePtr = (IntPtr)filePointer;
                    file = Marshal.PtrToStringAuto(openFileName.filePtr);
                }            
            }

            //第一条字符串为文件夹路径，需要再拼成完整的文件路径
            if (list.Count > 1)
            {
                for (int i = 1; i < list.Count; i++)
                {
                    list[i] = System.IO.Path.Combine(list[0], list[i]);
                }

                list = list.Skip(1).ToList();
            }

            Marshal.FreeHGlobal(filePtr);
            return list;
        }

测试 ：

 static void Main(string[] args)
        {
            var files = BrowseMultiFile("全部文件\0*.*\0\0");
            foreach (var item in files)
            {
                Console.WriteLine(item);
            }
        }

示例代码