HELP! How do I set the RichTextBox.SelectionFont FontFamily without changing the Style?

Question

One of the controls in my application limits a user to be able to change only the font style (B, I, U) and colour of the text. I have created a custom control which inherits from the RichTextBox for this purpose. I am able to intercept CTRL-V, and set the font of the pasted text to SystemFonts.DefaultFont. The problem I am currently facing is if the pasted text contains, for example, half bold half regular style - the bold is lost.

i.e. 'Foo**Bar**' will just paste as 'FooBar'.

My only idea currently is to go through the text character by character (VERY slow), and do something like:

public class MyRichTextBox : RichTextBox
{

private RichTextBox hiddenBuffer = new RichTextBox();

/// <summary>
/// This paste will strip the font size, family and alignment from the text being pasted.
/// </summary>
public void PasteUnformatted()
{
    this.hiddenBuffer.Clear();
    this.hiddenBuffer.Paste();

    for (int x = 0; x < this.hiddenBuffer.TextLength; x++)
    {
        // select the next character
        this.hiddenBuffer.Select(x, 1);

        // Set the font family and size to default
        this.hiddenBuffer.SelectionFont = new Font(SystemFonts.DefaultFont.FontFamily, SystemFonts.DefaultFont.Size, this.hiddenBuffer.SelectionFont.Style);
    }

    // Reset the alignment
    this.hiddenBuffer.SelectionAlignment = HorizontalAlignment.Left;

    base.SelectedRtf = this.hiddenBuffer.SelectedRtf;
    this.hiddenBuffer.Clear();
}

}

Can anyone think of a cleaner (and faster) solution?

Answer 1

'nobugz' over on the MSDN Forums answered this for me (I needed an answer quickly, so after almost a day of tumbleweed from SO, I had to look elsewhere - don't judge me!):

using System.Runtime.InteropServices;
...
        public static bool SetRtbFace(RichTextBox rtb, Font font, bool selectionOnly) {
            CHARFORMATW fmt = new CHARFORMATW();
            fmt.cbSize = Marshal.SizeOf(fmt);
            fmt.szFaceName = font.FontFamily.Name;
            fmt.dwMask = 0x20000000;  // CFM_FACE
            return IntPtr.Zero != SendMessage(rtb.Handle, 0x444, (IntPtr)(selectionOnly ? 1 : 4), fmt);
        }
        [StructLayout(LayoutKind.Sequential, Pack = 4)]
        private class CHARFORMATW {
            public int cbSize;
            public int dwMask;
            public int dwEffects;
            public int yHeight;
            public int yOffset;
            public int crTextColor;
            public byte bCharSet;
            public byte bPitchAndFamily;
            [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 0x40)]
            public string szFaceName;
        }

        [DllImport("user32.dll", CharSet = CharSet.Auto)]
        private static extern IntPtr SendMessage(IntPtr hWnd, int msg, IntPtr wParam, CHARFORMATW lParam);

Answer 2

For those wanting a Delphi answer, an extract to give you the basic idea:

using RichEdit; //reqd. for the constants and types

var
  chformat : TCharFormat2;
  fontname : string;

begin
  FillChar(chformat,sizeof(chformat),0);
  chformat.cbSize := sizeof(chformat);
  //only modify the szFaceName field, height etc. left alone
  chformat.dwMask :=  CFM_FACE; 
  //get the fontname set by the user
  fontname := AdvFontSelector1.Text;
  strpcopy(chformat.szFaceName,fontname);
  RichEdit1.Perform(EM_SETCHARFORMAT, SCF_SELECTION, lparam(@chformat));
end;