Richtextbox convert a line number to scroll bar position

Question

I'm able now to synchronize my two RichTextBox using this potion of code:

private const int SB_HORZ = 0x0;
private const int SB_VERT = 0x1;
private const int WM_HSCROLL = 0x114;
private const int WM_VSCROLL = 0x115;
private const int SB_THUMBPOSITION = 4;
[DllImport("user32.dll", CharSet = CharSet.Auto)]
private static extern int GetScrollPos(int hWnd, int nBar);
[DllImport("user32.dll")]
private static extern int SetScrollPos(IntPtr hWnd, int nBar, int nPos, bool bRedraw);
[DllImport("user32.dll")]
private static extern bool PostMessageA(IntPtr hWnd, int nBar, int wParam, int lParam);
internal int HScrollPos
{
    private get { return GetScrollPos((int)this.Handle, SB_HORZ); }
    set
    {
        SetScrollPos((IntPtr)this.Handle, SB_HORZ, value, true);
        PostMessageA((IntPtr)this.Handle, WM_HSCROLL, SB_THUMBPOSITION + 0x10000 * value, 0);
    }
}
internal int VScrollPos
{
    get { return GetScrollPos((int)this.Handle, SB_VERT); }
    set
    {
        SetScrollPos((IntPtr)this.Handle, SB_VERT, value, true);
        PostMessageA((IntPtr)this.Handle, WM_VSCROLL, SB_THUMBPOSITION + 0x10000 * value, 0);
    }
}

I can synchronize the RichTextBoxes while key down ,up and Vscroll event. Indeed this is not my goal, I want to synchronize my RichTextBoxes basing on the content, What do I need:

• Get the current line form non-selected RichTextBox.
• Set Scroll bar position using line number in the other RichTextBox (without losing the focus from the current one).
• Get line number using scroll bar position.

---

Note: you are welcome to ask if you need any more details.
Thanks in advance.

Answer 1

From what I understand, you need to synchronize scrolling on 2 RichTextBoxes based on the line number. Leave me a comment if I misunderstood it.

RichTextBox extended :

public class RichTextBoxEx : RichTextBox
{
    // combination of multiple events that may cause focus(caret) to change
    public event EventHandler FocusChanged;

    public RichTextBoxEx()
    {
        this.KeyPress += (s, e) => RaiseFocusChanged();
        this.KeyDown += (s, e) => RaiseFocusChanged();
        this.KeyUp += (s, e) => RaiseFocusChanged();
        this.MouseClick += (s, e) => RaiseFocusChanged();
    }

    private void RaiseFocusChanged()
    {
        var focusChanged = FocusChanged;
        if (focusChanged != null)
        {
            focusChanged(this, null);
        }
    }

    public int GetFirstSelectedLine()
    {
        var index = GetFirstCharIndexOfCurrentLine();
        return GetLineFromCharIndex(index);
    }
    public int GetFirstVisibleLine()
    {
        var index = GetCharIndexFromPosition(new Point(1, 1));
        return GetLineFromCharIndex(index);
    }

    public void ScrollToLine(int line)
    {
        if (line < 0)
            throw new ArgumentOutOfRangeException("line cannot be less than 0");

        // save the current selection to be restored later
        var selection = new { SelectionStart, SelectionLength };

        // select that line and scroll it to
        Select(GetFirstCharIndexFromLine(line) + 1, 0);
        ScrollToCaret();

        // restore selection
        Select(selection.SelectionStart, selection.SelectionLength);
    }
}

Usage :

void Main()
{
    var mainScreenArea = Screen.PrimaryScreen.WorkingArea;

    var rich1 = new RichTextBoxEx() { Width = mainScreenArea.Width / 2 - 10, Dock = DockStyle.Left };
    var rich2 = new RichTextBoxEx() { Width = mainScreenArea.Width / 2 - 10, Dock = DockStyle.Right };
    rich1.LoadFile(__RTF_FILE_0__);
    rich2.LoadFile(__RTF_FILE_1__);

    // pick one :
    // synchronize by focus
    rich1.FocusChanged += (s, e) => rich2.ScrollToLine(rich1.GetFirstSelectedLine());
    // synchronize by viewbox
    // rich1.VScroll += (s, e) => rich2.ScrollToLine(rich1.GetFirstVisibleLine());

    var form = new Form();
    form.Controls.Add(rich1);
    form.Controls.Add(rich2);

    form.WindowState = FormWindowState.Maximized;
    form.ShowDialog()
}