Drag N Drop controls in a GridPanel

Question

I have been fooling around with dragging and dropping controls in a grid panel in delphi 2010. Move a panel/button/whateever the contents are from one cell to another cell. Replacing existing or swapping places. I have not figured out how I know which cell was dropped on because they work with column indexes and also row indexes.

so if I have a gridpanel which has 3 columns and 3 rows, and I have a button in cell 1/1... and I drag that button from 1/1 into 3/3 how can I get that cell location from the dragdrop event? I get the x,y coords on the drop but how can I determine the cell from that?

Answer 1

You can use TGridPanel.CellRect to get the bounding rectangle for each of the cells. Here's an example of how to use CellRect:

// GP: TGridPanel
// This is the "OnDragDrop" handler.

procedure TForm13.GPDragDrop(Sender, Source: TObject; X, Y: Integer);
var DropPoint: TPoint;
    CellRect: TRect;
    i_col, i_row: Integer;
begin
  if Source = Panel1 then // Simple test, is this a drop I want to handle?
  begin
    DropPoint := Point(X, Y); // Where did the suer drop? We need this so we can easily call PtInRect
    for i_col := 0 to GP.ColumnCollection.Count-1 do
      for i_row := 0 to GP.RowCollection.Count-1 do
      begin
        CellRect := GP.CellRect[i_col, i_row]; // Get the bounding rect for Col[i_col, i_row]
        if PtInRect(CellRect, DropPoint) then
        begin
          // Panel1 was dropped over Cell[i_col, i_row]
        end;
      end;
  end;
end;

Answer 2

Based on Cosmin's answer (which is a nice starting point but does not work in real-life).

My code is in C++ but since it is a "clone" of Consmin's answer, Delphi users may easily understand it (and see what was changed).
PS: note that I drag TPanels instead of TButtons (a very minor change).

void __fastcall TfrmVCL::ButtonDragDrop(TObject *Sender, TObject *Source, int X, int Y)
{
  TRect CurCellRect;
  TRect DestCellRect;
  int Col;
  int Row;
  int srcCol; int srcRow;
  int destCol; int destRow;
  int srcIndex; int destIndex;
  TPanel *SrcBtn;
  TPanel *DestBtn;

  SrcBtn = dynamic_cast<TPanel *>(Source);
  if (SrcBtn)
     {
     int ColCount = GridPnl->ColumnCollection->Count ;
     int RowCount = GridPnl->RowCollection->Count ;

     // SOURCE
     srcIndex = GridPnl->ControlCollection->IndexOf( SrcBtn );
     srcCol   = GridPnl->ControlCollection->Items[ srcIndex ]->Column;  // the column for the dragged button
     srcRow   = GridPnl->ControlCollection->Items[ srcIndex ]->Row;

     // DESTINATION
     // we get coordinates of the button I drag onto
     DestBtn= dynamic_cast<TPanel *>(Sender);
     if (!DestBtn) return;
     destIndex    = GridPnl->ControlCollection->IndexOf( DestBtn );
     destCol      = GridPnl->ControlCollection->Items[ destIndex ]->Column;  // the column for the dragged button
     destRow      = GridPnl->ControlCollection->Items[ destIndex ]->Row;
     DestCellRect = GridPnl->CellRect[ destCol ][ destRow ];

     // Check all cells
     for ( Col = 0 ; Col < ColCount ; Col++ )
        {
        for ( Row = 0 ; Row < RowCount ; Row++ )
           {
             // Get the bounding rect for this cell
             CurCellRect = GridPnl->CellRect[ Col ][ Row ];

             if (IntersectRect_ForReal(DestCellRect, CurCellRect))
                {
                GridPnl->ControlCollection->Items[srcIndex]->SetLocation(Col, Row, false);
                return;
                }
             else
               lblCurCellRect->Caption= "NO HIT";
           }
        }
     }
}