你在正确的轨道上。有两种有效的方式来显示打开的文件对话框。较新的方法使用IFileOpenDialog（扩展IFileDialog）。使用此方法，过滤器描述和文件规范使用COMDLG_FILTERSPEC 结构定义。这让分开的人进入了自己的领域，这更自然。
如果您想使用此方法从组合框中删除文件规范，那么您必须添加自己的自定义控件或操作对话框上的组合框控件。虽然这会变得混乱，但应该是可行的。
老派方法使用GetOpenFileName 和OPENFILENAME 结构。这个技巧是可以显示一个旧外观或新外观的对话框。外观由 OPENFILENAME 结构中的设置决定，如 here 所述。
WinForms OpenFileDialog 的问题在于，当 AutoUpgradeEnabled 为 true 时，它们要么使用 IFileOpenDialog，而当 AutoUpgradeEnabled 为 false 时，它们使用旧外观的 GetOpenFileName。
WPF 版本没有给您选择，但仍使用与 WinForms 相同的逻辑，但会根据需要自动执行。对于 .NET 4 中的 WPF 也是如此，在以前的版本中，它只会使用带有旧外观的 GetOpenFileName。
Paint 最有可能使用具有新外观的 GetOpenFileName。这是一个 C# 示例：
private delegate IntPtr WndProc(IntPtr hWnd, int msg, IntPtr wParam, IntPtr lParam);
private const int OFN_ALLOWMULTISELECT = 0x00000200;
private const int OFN_CREATEPROMPT = 0x00002000;
private const int OFN_DONTADDTORECENT = 0x02000000;
private const int OFN_ENABLEHOOK = 0x00000020;
private const int OFN_ENABLEINCLUDENOTIFY = 0x00400000;
private const int OFN_ENABLESIZING = 0x00800000;
private const int OFN_ENABLETEMPLATE = 0x00000040;
private const int OFN_ENABLETEMPLATEHANDLE = 0x00000080;
private const int OFN_EXPLORER = 0x00080000;
private const int OFN_EXTENSIONDIFFERENT = 0x00000400;
private const int OFN_FILEMUSTEXIST = 0x00001000;
private const int OFN_FORCESHOWHIDDEN = 0x10000000;
private const int OFN_HIDEREADONLY = 0x00000004;
private const int OFN_LONGNAMES = 0x00200000;
private const int OFN_NOCHANGEDIR = 0x00000008;
private const int OFN_NODEREFERENCELINKS = 0x00100000;
private const int OFN_NOLONGNAMES = 0x00040000;
private const int OFN_NONETWORKBUTTON = 0x00020000;
private const int OFN_NOREADONLYRETURN = 0x00008000;
private const int OFN_NOTESTFILECREATE = 0x00010000;
private const int OFN_NOVALIDATE = 0x00000100;
private const int OFN_OVERWRITEPROMPT = 0x00000002;
private const int OFN_PATHMUSTEXIST = 0x00000800;
private const int OFN_READONLY = 0x00000001;
private const int OFN_SHAREAWARE = 0x00004000;
private const int OFN_SHOWHELP = 0x00000010;
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
public class OPENFILENAME_I {
public int lStructSize;
public IntPtr hwndOwner;
public IntPtr hInstance;
public string lpstrFilter;
public IntPtr lpstrCustomFilter;
public int nMaxCustFilter;
public int nFilterIndex;
public IntPtr lpstrFile;
public int nMaxFile = 260;
public IntPtr lpstrFileTitle;
public int nMaxFileTitle = 260;
public string lpstrInitialDir;
public string lpstrTitle;
public int Flags;
public short nFileOffset;
public short nFileExtension;
public string lpstrDefExt;
public IntPtr lCustData;
public WndProc lpfnHook;
public string lpTemplateName;
public IntPtr pvReserved;
public int dwReserved;
public int FlagsEx;
}
[DllImport("comdlg32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
private static extern bool GetOpenFileName([In, Out] OPENFILENAME_I ofn);
private void ShowOpenFileDialog() {
OPENFILENAME_I ofn = new OPENFILENAME_I();
ofn.lStructSize = Marshal.SizeOf(typeof(OPENFILENAME_I));
ofn.lpstrFilter = "Text Files (*.txt)\0*.txt\0All Files\0*.*\0\0";
ofn.nFilterIndex = 0;
//ofn.Flags = OFN_EXPLORER | OFN_ENABLEHOOK | OFN_ENABLESIZING | OFN_NODEREFERENCELINKS | OFN_HIDEREADONLY | OFN_PATHMUSTEXIST | OFN_FILEMUSTEXIST;
ofn.Flags = OFN_ENABLESIZING | OFN_NODEREFERENCELINKS | OFN_HIDEREADONLY | OFN_PATHMUSTEXIST | OFN_FILEMUSTEXIST;
GetOpenFileName(ofn);
}
您可以尝试重新添加OFN_EXPLORER 和/或OFN_ENABLEHOOK 标志，它会恢复到旧外观。但照原样，上面的代码将显示一个打开的文件对话框，其中所有文件都没有显示它的文件规范。