Implement “drag and fill” functionality in WPF dat

Question

We are developing an app that utilises a data grid. Most of the grid's functionality will be fairly standard stuff - styling cells, in-cell editing, sorting, etc. However one requirement is to provide "drag and fill" functionality, like Excel. This is where you select one or more cells inside a row, which then get a thick border drawn around them. The border has a small square on its bottom-right corner, and when you drag this down Excel copies the selected cell values to the rows below.

This sounds like a frightening thing to try and implement using the .Net WPF data grid (and no commercial data grid component provides this feature either). Has anyone developed a similar feature, or suggest possible approaches to accomplishing this? Plain old copy & paste is not an option!

Answer 1

Here are some tips to draw a thick line around your selected cells in a datagrid:

• Subscribe to the datagrid's SelectedCellsChanged event.
• In the event handler, get the adorner layer of the datagrid and add a custom adorner to it if the number of selected cells > 0 and if there is no (cached) adornerlayer yet. Pass the datagrid via the adorner's constructor. If the number of selected cells == 0 and the cached adornerlayer != null, remove the adorner from the adorner layer. At the end of the event handler, call adornerLayer.Update(datagrid)

• Use the following CustomAdorner class:

  public class DataGridSelectionAdorner : Adorner {
      private readonly DataGrid datagrid;
      private readonly SolidColorBrush backgroundBrush = new SolidColorBrush(Color.FromArgb(30, 0, 0, 0));
      readonly Pen pen = new Pen(new SolidColorBrush(Colors.Black), 1);
      private readonly Dictionary<DataGridCellInfo, int[]> cellInfoToTableRowAndColumn = new Dictionary<DataGridCellInfo, int[]>();
  
      public DataGridSelectionAdorner(UIElement adornedElement)
          : base(adornedElement) {
          datagrid = (DataGrid)adornedElement;
          pen.DashStyle = new DashStyle(new[] { 3.0, 3.0 }, 0);
          IsHitTestVisible = false;
      }
  
      protected override void OnRender(DrawingContext drawingContext) {
          ItemContainerGenerator generator = datagrid.ItemContainerGenerator;
          IEnumerable<int> rows =
                  datagrid.SelectedCells.Select(c =>
                      generator.IndexFromContainer(
                          generator.ContainerFromItem(c.Item)
                      )
                  );
          IEnumerable<int> columns = datagrid.SelectedCells.Select(
              c => c.Column.DisplayIndex
          );
          int minRow = rows.Min();
          int maxRow = rows.Max();
          int minColumn = columns.Min();
          int maxColumn = columns.Max();
  
          foreach (var cell in datagrid.SelectedCells) {
              int row = generator.IndexFromContainer(generator.ContainerFromItem(cell.Item));
              int column = cell.Column.DisplayIndex;
              cellInfoToTableRowAndColumn[cell] = new[] { row, column };
          }
  
          var topLeft = cellInfoToTableRowAndColumn.First(c => c.Value[0] == minRow && c.Value[1] == minColumn).Key;
          var bottomRight = cellInfoToTableRowAndColumn.First(c => c.Value[0] == maxRow && c.Value[1] == maxColumn).Key;
  
          var topLeftCell = GetDataGridCell(topLeft);
          var bottomRightCell = GetDataGridCell(bottomRight);
  
          const double marginX = 4.5;
          const double marginY = 3.5;
          Point topLeftPoint = topLeftCell.TranslatePoint(new Point(marginX, marginY), datagrid);
          Point bottomRightPoint = bottomRightCell.TranslatePoint(
              new Point(bottomRightCell.RenderSize.Width - marginX, bottomRightCell.RenderSize.Height - marginY),
              datagrid
          );
  
          drawingContext.DrawRectangle(backgroundBrush, pen, new Rect(topLeftPoint, bottomRightPoint));
      }
  
      private static DataGridCell GetDataGridCell(DataGridCellInfo cellInfo) {
          var cellContent = cellInfo.Column.GetCellContent(cellInfo.Item);
          if (cellContent != null)
              return (DataGridCell)cellContent.Parent;
          return null;
      }
  }