I am trying to get the font size of a running instance of WordPad (based on
Rich Edit). When I called the following function in my Windows Form which is

shown but not activated (SW_SHOWNOACTIVATE), WordPad crashed with the dialog
message - "WordPad MFC Application has encountered a problem and needs

to close. We are sorry for the inconvenience". I also found out that if I
run a test Windows Forms application containing a RichTextBox, then the same
problem

(crashing) occurs as with WordPad.  The problem has to do with the Rich Edit
control when it receives the message EM_GETCHARFORMAT through interop. I'd be

very grateful for any advices on how to resolve this issue.

        /// <summary>
        /// Get the height of the font currently being used in the RichEdit control
        /// <summary>
        private int GetFontHeightFromRichEditControl()
        {
            int fontHeight  = 0;

            IntPtr idAttached = User32.GetWindowThreadProcessId(this.Handle,
IntPtr.Zero);
            IntPtr idAttachedTo =
User32.GetWindowThreadProcessId(User32.GetForegroundWindow(), IntPtr.Zero);
           
            // Attached   
            if (User32.AttachThreadInput(idAttached, idAttachedTo, 1) == IntPtr.Zero)
            {
                return fontHeight;
            }

            CHARFORMAT cf = new CHARFORMAT();
            cf.cbSize = Marshal.SizeOf(cf);
       
            // Get the focus window
            IntPtr focusWindow =  User32.GetFocus();

            SendMessage(focusWindow, User32.EM_GETCHARFORMAT, SCF_SELECTION, ref cf);
       
            if ((cf.dwMask & CFM_SIZE) == CFM_SIZE)
            {
                fontHeight = cf.yHeight / 20;    // yHeight is in 1/20 pt
            }
           
            // Deattached
            User32.AttachThreadInput(idAttached, idAttachedTo, 0);
           
            return fontHeight;
        }

[DllImport("user32")] public static extern IntPtr
GetWindowThreadProcessId(IntPtr hWnd, IntPtr lpdwProcessId);
[DllImport("user32")] public static extern IntPtr AttachThreadInput(IntPtr
idAttach, IntPtr idAttachTo, int fAttach);
[DllImport("user32")] public static extern int SendMessage(IntPtr hWnd, int
wMsg, int wParam, ref CHARFORMAT lParam);

    [StructLayout( LayoutKind.Sequential )]
    public 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;
    }