Changing font for richtextbox without losing formatting

Question

How to change the font of all the contents of a richtextbox without losing formatting?

I am trying to use

rtb.SelectAll();
rtb.SelectionFont = new Font(fontName,...);

but the font constructor has to take besides the font type either the font style (bold, italics, ...) or font size. So using this would change the style/size of all the content of the richtextbox.

Of course the same applies for any selection in the richtextbox.

Answer 1

This is a RichTextBox that I have used in the past. It's spliced together from code found here at Stack Overflow and the internet at large:

public class RichBox : RichTextBox {
  private const UInt32 CFM_BOLD = 0x00000001;
  private const UInt32 CFM_ITALIC = 0x00000002;
  private const UInt32 CFM_UNDERLINE = 0x00000004;
  private const UInt32 CFM_STRIKE = 0x00000008;
  private const UInt32 CFM_FACE = 0x20000000;
  private const UInt32 CFM_SIZE = 0x80000000;

  private const int WM_PAINT = 0xF;
  private const int WM_SETREDRAW = 0xB;
  private const int WM_USER = 0x400;

  private const int EM_SETCHARFORMAT = (WM_USER + 68);
  private const int SCF_SELECTION = 0x0001;
  private const int EM_GETEVENTMASK = WM_USER + 59;
  private const int EM_SETEVENTMASK = WM_USER + 69;
  private const int EM_GETSCROLLPOS = WM_USER + 221;
  private const int EM_SETSCROLLPOS = WM_USER + 222;

  [StructLayout(LayoutKind.Sequential)]
  private struct CHARFORMAT {
    public int cbSize;
    public uint dwMask;
    public uint dwEffects;
    public int yHeight;
    public int yOffset;
    public int crTextColor;
    public byte bCharSet;
    public byte bPitchAndFamily;
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 32)]
    public char[] szFaceName;
    public short wWeight;
    public short sSpacing;
    public int crBackColor;
    public int LCID;
    public uint dwReserved;
    public short sStyle;
    public short wKerning;
    public byte bUnderlineType;
    public byte bAnimation;
    public byte bRevAuthor;
  }

  [DllImport("kernel32.dll", CharSet = CharSet.Auto)]
  private static extern IntPtr LoadLibrary(string lpFileName);

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

  [DllImport("user32.dll")]
  private static extern IntPtr SendMessage(IntPtr hWnd, Int32 wMsg, Int32 wParam, ref Point lParam);

  [DllImport("user32.dll")]
  private static extern IntPtr SendMessage(IntPtr hWnd, Int32 wMsg, Int32 wParam, IntPtr lParam);

  private bool frozen = false;
  private Point lastScroll = Point.Empty;
  private IntPtr lastEvent = IntPtr.Zero;
  private int lastIndex = 0;
  private int lastWidth = 0;

  protected override CreateParams CreateParams {
    get {
      var cp = base.CreateParams;
      if (LoadLibrary("msftedit.dll") != IntPtr.Zero) {
        cp.ClassName = "RICHEDIT50W";
      }
      return cp;
    }
  }

  [Browsable(false)]
  [DefaultValue(typeof(bool), "False")]
  [DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)]
  public bool FreezeDrawing {
    get { return frozen; }
    set {
      if (value != frozen) {
        frozen = value;
        if (frozen) {
          this.SuspendLayout();
          SendMessage(this.Handle, WM_SETREDRAW, 0, IntPtr.Zero);
          SendMessage(this.Handle, EM_GETSCROLLPOS, 0, ref lastScroll);
          lastEvent = SendMessage(this.Handle, EM_GETEVENTMASK, 0, IntPtr.Zero);
          lastIndex = this.SelectionStart;
          lastWidth = this.SelectionLength;
        } else {
          this.Select(lastIndex, lastWidth);
          SendMessage(this.Handle, EM_SETEVENTMASK, 0, lastEvent);
          SendMessage(this.Handle, EM_SETSCROLLPOS, 0, ref lastScroll);
          SendMessage(this.Handle, WM_SETREDRAW, 1, IntPtr.Zero);
          this.Invalidate();
          this.ResumeLayout();
        }
      }
    }
  }

  [Browsable(false)]
  [DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)]
  public Font CurrentFont {
    get {
      Font result = this.Font;
      if (this.SelectionLength == 0) {
        result = SelectionFont;
      } else {
        using (RichBox rb = new RichBox()) {
          rb.FreezeDrawing = true;
          rb.SelectAll();
          rb.SelectedRtf = this.SelectedRtf;
          rb.Select(0, 1);
          result = rb.SelectionFont;
        }
      }
      return result;
    }
  }

  [Browsable(false)]
  [DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)]
  public string SelectionFontName {
    get { return CurrentFont.FontFamily.Name; }
    set {
      CHARFORMAT cf = new CHARFORMAT();
      cf.cbSize = Marshal.SizeOf(cf);
      cf.szFaceName = new char[32];
      cf.dwMask = CFM_FACE;
      value.CopyTo(0, cf.szFaceName, 0, Math.Min(31, value.Length));
      IntPtr lParam = Marshal.AllocCoTaskMem(Marshal.SizeOf(cf));
      Marshal.StructureToPtr(cf, lParam, false);
      SendMessage(this.Handle, EM_SETCHARFORMAT, SCF_SELECTION, lParam);
    }
  }

  [Browsable(false)]
  [DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)]
  public float SelectionFontSize {
    get { return CurrentFont.Size; }
    set {
      CHARFORMAT cf = new CHARFORMAT();
      cf.cbSize = Marshal.SizeOf(cf);
      cf.dwMask = CFM_SIZE;
      cf.yHeight = Convert.ToInt32(value * 20);
      IntPtr lParam = Marshal.AllocCoTaskMem(Marshal.SizeOf(cf));
      Marshal.StructureToPtr(cf, lParam, false);
      SendMessage(this.Handle, EM_SETCHARFORMAT, SCF_SELECTION, lParam);
    }
  }

  [Browsable(false)]
  [DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)]
  public bool SelectionBold {
    get { return CurrentFont.Bold; }
    set {
      CHARFORMAT cf = new CHARFORMAT();
      cf.cbSize = Marshal.SizeOf(cf);
      cf.dwMask = CFM_BOLD;
      cf.dwEffects = value ? CFM_BOLD : 0;
      IntPtr lParam = Marshal.AllocCoTaskMem(Marshal.SizeOf(cf));
      Marshal.StructureToPtr(cf, lParam, false);
      SendMessage(this.Handle, EM_SETCHARFORMAT, SCF_SELECTION, lParam);
    }
  }

  [Browsable(false)]
  [DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)]
  public bool SelectionItalic {
    get { return CurrentFont.Italic; }
    set {
      CHARFORMAT cf = new CHARFORMAT();
      cf.cbSize = Marshal.SizeOf(cf);
      cf.dwMask = CFM_ITALIC;
      cf.dwEffects = value ? CFM_ITALIC : 0;
      IntPtr lParam = Marshal.AllocCoTaskMem(Marshal.SizeOf(cf));
      Marshal.StructureToPtr(cf, lParam, false);
      SendMessage(this.Handle, EM_SETCHARFORMAT, SCF_SELECTION, lParam);
    }
  }

  [Browsable(false)]
  [DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)]
  public bool SelectionStrikeout {
    get { return CurrentFont.Strikeout; }
    set {
      CHARFORMAT cf = new CHARFORMAT();
      cf.cbSize = Marshal.SizeOf(cf);
      cf.dwMask = CFM_STRIKE;
      cf.dwEffects = value ? CFM_STRIKE : 0;
      IntPtr lParam = Marshal.AllocCoTaskMem(Marshal.SizeOf(cf));
      Marshal.StructureToPtr(cf, lParam, false);
      SendMessage(this.Handle, EM_SETCHARFORMAT, SCF_SELECTION, lParam);
    }
  }

  [Browsable(false)]
  [DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)]
  public bool SelectionUnderline {
    get { return CurrentFont.Underline; }
    set {
      CHARFORMAT cf = new CHARFORMAT();
      cf.cbSize = Marshal.SizeOf(cf);
      cf.dwMask = CFM_UNDERLINE;
      cf.dwEffects = value ? CFM_UNDERLINE : 0;
      IntPtr lParam = Marshal.AllocCoTaskMem(Marshal.SizeOf(cf));
      Marshal.StructureToPtr(cf, lParam, false);
      SendMessage(this.Handle, EM_SETCHARFORMAT, SCF_SELECTION, lParam);
    }
  }
}

It adds new properties such as SelectionBold, SelectionItalic, etc. where you can apply the attribute and not lose the other formatting of the text.

Answer 2

You can pass the new font name while keeping other values intact by using the existing richtextbox font properties. For changing only font name of a selected text, you need to do:

if (rtb.SelectionFont !=null)
    rtb.SelectionFont = new Font(fontName, rtb.SelectionFont.Size, rtb.SelectionFont.Style);

Note that above code will only work, if all the selected text has same formatting (font size, style etc). This is detected by checking the SelectionFont property first, it will be null if the selection contains a mix of styles.

Now to change the font name of all the contents of richtextbox while keeping other formatting intact, you need to loop through all the characters of the richtextbox and apply font name one by one.

for (int i = 0; i < rtb.TextLength; i++)
{
    rtb.Select(i, 1);
    rtb.SelectionFont = new Font(fontName, rtb.SelectionFont.Size, rtb.SelectionFont.Style);
}