ThisAddIn.cs (or a dedicated controller class)



using Excel = Microsoft.Office.Interop.Excel;

using System;

using System.Windows;

namespace YourAddIn

{

    public partial class ThisAddIn

    {

        private CellOverlayWindow overlay;

        private bool overlayActive;

        private bool editDirectlyPrev;

        private void ThisAddInStartup(object sender, System.EventArgs e)

        {

            overlay = new CellOverlayWindow();

            overlay.CommitAndHide += OverlayCommitAndHide;

            overlay.CancelAndHide += OverlayCancelAndHide;

            // Subscribe at Application level: one handler for all sheets

            Application.SheetSelectionChange += ApplicationSheetSelectionChange;

        }

        private void ThisAddInShutdown(object sender, System.EventArgs e)

        {

            Application.SheetSelectionChange -= ApplicationSheetSelectionChange;

            if (overlay != null)

            {

                overlay.Close();

            }

        }

        private void ApplicationSheetSelectionChange(object Sh, Excel.Range Target)

        {

            // Reposition and show overlay over Target, then DEFER focus.

            ShowOverlayFor(Target);

        }

        private void ShowOverlayFor(Excel.Range target)

        {

            if (target == null) return;

            var win = Application.ActiveWindow;

            if (win == null) return;

            // Compute screen rectangle of the cell in pixels (using Excel API)

            GetCellScreenRect(target, win, out int x, out int y, out int w, out int h);

            overlay.Left   = x;

            overlay.Top    = y;

            overlay.Width  = Math.Max(40, w);  // minimal width

            overlay.Height = Math.Max(20, h);

            if (!overlay.IsVisible)

                overlay.Show();

            // Disable in-cell edit while overlay is active (restore later)

            if (!overlayActive)

            {

                editDirectlyPrev = Application.EditDirectlyInCell;

                Application.EditDirectlyInCell = false;

                overlayActive = true;

            }

            // Set the text from the cell (optional)

            overlay.Editor.Text = Convert.ToString(target.Value2 ?? string.Empty);

            // Defer focus so Excel finishes its own activation

            overlay.FocusEditorDeferred();

            // If some environments still steal focus, uncomment fallback:

            // overlay.ForceWin32Focus();

        }

        private void OverlayCommitAndHide(object sender, EventArgs e)

        {

            try

            {

                var rng = (Excel.Range)Application.ActiveCell;

                if (rng != null)

                {

                    rng.Value2 = overlay.Editor.Text;

                }

            }

            catch { /* handle/log if needed / }

            finally

            {

                HideOverlayAndRestoreExcel();

            }

        }

        private void OverlayCancelAndHide(object sender, EventArgs e)

        {

            HideOverlayAndRestoreExcel();

        }

        private void HideOverlayAndRestoreExcel()

        {

            if (overlay?.IsVisible == true)

                overlay.Hide();

            if (overlayActive)

            {

                Application.EditDirectlyInCell = editDirectlyPrev;  // restore previous setting

                overlayActive = false;

            }

            // Return focus to Excel

            try

            {

                Application.ActiveWindow?.Activate();

            }

            catch { / ignore */ }

        }

        /// <summary>

        /// Converts the Excel Range rectangle (points) to screen pixels using Excel’s Window conversion helpers.

        /// </summary>

        private static void GetCellScreenRect(Excel.Range target, Excel.Window win,

                                              out int x, out int y, out int width, out int height)

        {

            // Range.Left/Top/Width/Height are in points relative to the sheet.

            double leftPt = (double)target.Left;

            double topPt  = (double)target.Top;

            double wPt    = (double)target.Width;

            double hPt    = (double)target.Height;

            // Convert points to screen pixels via ActiveWindow.PointsToScreenPixelsX/Y

            // Convert both corners then subtract.

            win.PointsToScreenPixelsX((int)Math.Round(leftPt), out x            win.PointsToScreenPixelsX((int)Math.Round(leftPt), out x);

            win.PointsToScreenPixelsY((int)Math.Round(topPt),  out y);

            int x2, y2;

            win.PointsToScreenPixelsX((int)Math.Round(leftPt + wPt), out x2);

            win.PointsToScreenPixelsY((int)Math.Round(topPt  + hPt), out y2);

            width  = Math.Max(1, x2 - x);

            height = Math.Max(1, y2 - y);

        }

        #region VSTO generated code

        private void InternalStartup()

        {

            this.Startup += new System.EventHandler(ThisAddInStartup);

            this.Shutdown += new System.EventHandler(ThisAddIn_Shutdown);

        }

        #endregion

    }

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