我已经为您准备了一个功能齐全的示例，使用发布的解决方案 here 利用 RTF 功能。
正如 Hans Passant 所写：解决方案相当棘手，有一些有效的替代方案可以实现。
顺便说一句，这是你的代码（重写）：
private bool CheckIfImage(string filename)
{
var valids = new[] {".jpeg", ".jpg", ".png", ".ico", ".gif", ".bmp", ".emp", ".wmf", ".tiff"};
return valids.Contains(System.IO.Path.GetExtension(filename));
}
private void openFileDialog2_FileOk(object sender, CancelEventArgs e)
{
if (CheckIfImage(openFileDialog2.FileName.ToLower()) == true)
embedImage(Image.FromFile(openFileDialog2.FileName));
else
MessageBox.Show("Invalid Image File Selected");
}
这是embedImage 方法：
private void embedImage(Image img)
{
var rtf = new StringBuilder();
// Append the RTF header
rtf.Append(@"{\rtf1\ansi\ansicpg1252\deff0\deflang1033");
// Create the font table using the RichTextBox's current font and append
// it to the RTF string
rtf.Append(GetFontTable(this.Font));
// Create the image control string and append it to the RTF string
rtf.Append(GetImagePrefix(img));
// Create the Windows Metafile and append its bytes in HEX format
rtf.Append(getRtfImage(img));
// Close the RTF image control string
rtf.Append(@"}");
richTextBox1.SelectedRtf = rtf.ToString();
}
这里有所有必要的方法：
private enum EmfToWmfBitsFlags
{
EmfToWmfBitsFlagsDefault = 0x00000000,
EmfToWmfBitsFlagsEmbedEmf = 0x00000001,
EmfToWmfBitsFlagsIncludePlaceable = 0x00000002,
EmfToWmfBitsFlagsNoXORClip = 0x00000004
};
private struct RtfFontFamilyDef
{
public const string Unknown = @"\fnil";
public const string Roman = @"\froman";
public const string Swiss = @"\fswiss";
public const string Modern = @"\fmodern";
public const string Script = @"\fscript";
public const string Decor = @"\fdecor";
public const string Technical = @"\ftech";
public const string BiDirect = @"\fbidi";
}
[DllImport("gdiplus.dll")]
private static extern uint GdipEmfToWmfBits(IntPtr _hEmf,
uint _bufferSize, byte[] _buffer,
int _mappingMode, EmfToWmfBitsFlags _flags);
private string GetFontTable(Font font)
{
var fontTable = new StringBuilder();
// Append table control string
fontTable.Append(@"{\fonttbl{\f0");
fontTable.Append(@"\");
var rtfFontFamily = new HybridDictionary();
rtfFontFamily.Add(FontFamily.GenericMonospace.Name, RtfFontFamilyDef.Modern);
rtfFontFamily.Add(FontFamily.GenericSansSerif, RtfFontFamilyDef.Swiss);
rtfFontFamily.Add(FontFamily.GenericSerif, RtfFontFamilyDef.Roman);
rtfFontFamily.Add("UNKNOWN", RtfFontFamilyDef.Unknown);
// If the font's family corresponds to an RTF family, append the
// RTF family name, else, append the RTF for unknown font family.
fontTable.Append(rtfFontFamily.Contains(font.FontFamily.Name) ? rtfFontFamily[font.FontFamily.Name] : rtfFontFamily["UNKNOWN"]);
// \fcharset specifies the character set of a font in the font table.
// 0 is for ANSI.
fontTable.Append(@"\fcharset0 ");
// Append the name of the font
fontTable.Append(font.Name);
// Close control string
fontTable.Append(@";}}");
return fontTable.ToString();
}
private string GetImagePrefix(Image _image)
{
float xDpi, yDpi;
var rtf = new StringBuilder();
using (Graphics graphics = CreateGraphics())
{
xDpi = graphics.DpiX;
yDpi = graphics.DpiY;
}
// Calculate the current width of the image in (0.01)mm
var picw = (int)Math.Round((_image.Width / xDpi) * 2540);
// Calculate the current height of the image in (0.01)mm
var pich = (int)Math.Round((_image.Height / yDpi) * 2540);
// Calculate the target width of the image in twips
var picwgoal = (int)Math.Round((_image.Width / xDpi) * 1440);
// Calculate the target height of the image in twips
var pichgoal = (int)Math.Round((_image.Height / yDpi) * 1440);
// Append values to RTF string
rtf.Append(@"{\pict\wmetafile8");
rtf.Append(@"\picw");
rtf.Append(picw);
rtf.Append(@"\pich");
rtf.Append(pich);
rtf.Append(@"\picwgoal");
rtf.Append(picwgoal);
rtf.Append(@"\pichgoal");
rtf.Append(pichgoal);
rtf.Append(" ");
return rtf.ToString();
}
private string getRtfImage(Image image)
{
// Used to store the enhanced metafile
MemoryStream stream = null;
// Used to create the metafile and draw the image
Graphics graphics = null;
// The enhanced metafile
Metafile metaFile = null;
try
{
var rtf = new StringBuilder();
stream = new MemoryStream();
// Get a graphics context from the RichTextBox
using (graphics = CreateGraphics())
{
// Get the device context from the graphics context
IntPtr hdc = graphics.GetHdc();
// Create a new Enhanced Metafile from the device context
metaFile = new Metafile(stream, hdc);
// Release the device context
graphics.ReleaseHdc(hdc);
}
// Get a graphics context from the Enhanced Metafile
using (graphics = Graphics.FromImage(metaFile))
{
// Draw the image on the Enhanced Metafile
graphics.DrawImage(image, new Rectangle(0, 0, image.Width, image.Height));
}
// Get the handle of the Enhanced Metafile
IntPtr hEmf = metaFile.GetHenhmetafile();
// A call to EmfToWmfBits with a null buffer return the size of the
// buffer need to store the WMF bits. Use this to get the buffer
// size.
uint bufferSize = GdipEmfToWmfBits(hEmf, 0, null, 8, EmfToWmfBitsFlags.EmfToWmfBitsFlagsDefault);
// Create an array to hold the bits
var buffer = new byte[bufferSize];
// A call to EmfToWmfBits with a valid buffer copies the bits into the
// buffer an returns the number of bits in the WMF.
uint _convertedSize = GdipEmfToWmfBits(hEmf, bufferSize, buffer, 8, EmfToWmfBitsFlags.EmfToWmfBitsFlagsDefault);
// Append the bits to the RTF string
foreach (byte t in buffer)
{
rtf.Append(String.Format("{0:X2}", t));
}
return rtf.ToString();
}
finally
{
if (graphics != null)
graphics.Dispose();
if (metaFile != null)
metaFile.Dispose();
if (stream != null)
stream.Close();
}
}
我建议你把它包装成你自己的UserControl。