Implementing code editor

Implementing code editor

The easiest (and limited) way to implement a code editor is to use a RichBox component in WinForms or WPF and replace the content by a highlighted RTF every time the text in the control changes. Something like this:

public partial class Form1 : Form
    {
        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        internal static extern int SendMessage(IntPtr hWnd, uint uMsg, int wParam, int lParam);

        [DllImport("user32.dll", CharSet = CharSet.Auto)]
        private static extern int GetScrollPos(int hWnd, int nBar);

        [DllImport("user32.dll")]
        public static extern int SetScrollPos(IntPtr hWnd, System.Windows.Forms.Orientation nBar, int nPos, bool bRedraw);

        private const uint WM_VSCROLL = 0x0115;
        private const uint WM_HSCROLL = 0x0114;
        private const int SB_THUMBPOSITION = 4;
        private const int WM_USER = 0x0400;
        private const int EM_SETEVENTMASK = (WM_USER + 69);
        private const int WM_SETREDRAW = 0x0b;
        private int OldEventMask;

        private readonly RtfHighlighter highlighter;

        public void BeginUpdate()
        {
            SendMessage(this.Handle, WM_SETREDRAW, 0, 0);
            OldEventMask = SendMessage(this.Handle, EM_SETEVENTMASK, 0, 0);
        }

        public void EndUpdate()
        {
            SendMessage(this.Handle, WM_SETREDRAW, 1, 0);
            SendMessage(this.Handle, EM_SETEVENTMASK, 0, OldEventMask);
            editor.Invalidate();
        }

        public Form1()
        {
            InitializeComponent();

            highlighter = new RtfHighlighter(new Orionsoft.PrismSharp.Tokenizing.Tokenizer(), Theme.Load(ThemeNames.Vs))
            {
                Font = "Consolas"
            };
        }

        private void editor_TextChanged(object sender, EventArgs e)
        {
            var vertPos = GetScrollPos((int)editor.Handle, (int)Orientation.Vertical);
            var horizPos = GetScrollPos((int)editor.Handle, (int)Orientation.Horizontal);
            BeginUpdate();

            int i = editor.SelectionStart;
            var hl = highlighter.Highlight(editor.Text + "\n", "csharp");

            var stream = new MemoryStream(ASCIIEncoding.Default.GetBytes(hl));
            this.editor.LoadFile(stream, RichTextBoxStreamType.RichText);

            SendMessage(editor.Handle, WM_VSCROLL, vertPos << 16 | SB_THUMBPOSITION, 0);
            SendMessage(editor.Handle, WM_HSCROLL, horizPos << 16 | SB_THUMBPOSITION, 0);
            SetScrollPos(editor.Handle, Orientation.Vertical, vertPos, true);
            SetScrollPos(editor.Handle, Orientation.Horizontal, horizPos, true);
            editor.SelectionStart = i;

            EndUpdate();
        }
    }
}

However, this works fine only with shorter texts, because RichBox (especially WPF RichBox) gets pretty slow with long texts.

If you need a code editor working well with long source codes, you need to create a custom control that renders (and tokenizes) only the visible part of the code. You can use TokenizeRange or HighlightRange methods for this purpose. Still, implementing of the custom control must be done. A good starter could be the CodeBox 2 that handles this issue.