Drag and Drop in a TStringGrid

I've got a new application with a TStringGrid that contains simple text.  I'd like to be able to swap the contents of two cells with a simple drag and drop but this seems to be a control that doesn't behave as expected.

When I click on a cell, the cell highlights by a double line around the cell.  If I click on another control the cell background changes color and looks like a normal highlighted cell.

I cannot drop to a cell.  The OnClick() method is called and I can clearly see that I'm entering the cell, but the OnDragDrop() method is never called.

Any thoughts on how to use this control would be appreciated.

Thanks,
Kent

LVL 46
Kent OlsenData Warehouse Architect / DBAAsked:
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Jose ParrotConnect With a Mentor Graphics ExpertCommented:
Well, that is:
Let DragMode in default dmManual.
The code below permits cell editing (of course with goEditing = true) and change contents between cells when we make drag & drop.

void __fastcall TForm1::StringGrid1MouseDown(TObject *Sender,
      TMouseButton Button, TShiftState Shift, int X, int Y)
{
    globalCol=X/StringGrid1->DefaultColWidth;
    globalRow=Y/StringGrid1->DefaultRowHeight;
    globalAS = StringGrid1->Cells[globalCol][globalRow];
}
//---------------------------------------------------------------------------

void __fastcall TForm1::StringGrid1MouseUp(TObject *Sender,
      TMouseButton Button, TShiftState Shift, int X, int Y)
{
    int localCol=X/StringGrid1->DefaultColWidth;
    int localRow=Y/StringGrid1->DefaultRowHeight;
    if (globalAS != "")
    {
        AnsiString localAS = StringGrid1->Cells[localCol][localRow];
        StringGrid1->Cells[localCol][localRow] = globalAS;
        StringGrid1->Cells[globalCol][globalRow] = localAS;
    }
}
//---------------------------------------------------------------------------

Ugly to use globals, but this is the simpler (BTW not wrong) way to make the temporary storage of col, row and string, as tag can have just one int.

Jose
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Jose ParrotGraphics ExpertCommented:
Hi,

Let's use three TLabel (Label1, Label2 and Label3) all with DragMode set to dmAutomatic.
And one TStringGrid (StringGrid1).
Use the code below to drag the caption from each label to any cell at the grid.

//---------------------------------------------------------------------------
void __fastcall TForm1::StringGrid1DragOver(TObject *Sender,
      TObject *Source, int X, int Y, TDragState State, bool &Accept)
{
   Accept = Source->ClassNameIs("TLabel");    
}
//---------------------------------------------------------------------------
void __fastcall TForm1::StringGrid1DragDrop(TObject *Sender,
      TObject *Source, int X, int Y)
{
  if (Sender->ClassNameIs("TStringGrid") && Source->ClassNameIs("TLabel"))
  {
    TStringGrid *DestGrid = (TStringGrid *)Sender;
    int localCol=X/StringGrid1->DefaultColWidth;
    int localRow=Y/StringGrid1->DefaultRowHeight;
    DestGrid->Cells[localCol][localRow]=((TLabel *)Source)->Caption;
  }
}

Jose
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Jose ParrotGraphics ExpertCommented:
Sorry... Misunderstand the question.
Hummm... interesting problem, both source and destin are the same component...
Let's think a bit more...
Jose
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Kent OlsenData Warehouse Architect / DBAAuthor Commented:

Yeah.  :)  This is an interesting poser that has a real use.

The simplest thing may be to just use a different type of control, but at this point I'd rather see if a reasonable solution exists.
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Kent OlsenData Warehouse Architect / DBAAuthor Commented:


Ahhh...   Just use the MouseDown and MouseUp events.....

Sometimes the simple solutions evade us.  I'll try it.  :)


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Kent OlsenData Warehouse Architect / DBAAuthor Commented:
Hi Jose,

That worked better than I could have possibly hoped.  :)  kudos.

I'm going to post the basic code and leave the question open for a few more days.  This new EE protocol seems to bury the new questions as soon as they are closed.

Kent

// Set DragMode to dmManual
// Set goEditing to true

// In MainForm

  bool Swapping;        // Set to false in the instantiator
  int    SwapFromX;
  int    SwapFromY;

// Methods

void __fastcall TMainForm::GridMouseDown(TObject *Sender,
      TMouseButton Button, TShiftState Shift, int X, int Y)
{
  Grid->MouseToCell (X, Y, SwapFromX, SwapFromY);
  if (SwapFromX < Grid->ColCount && SwapFromY < Grid->RowCount)
  {
    StatusBar->SimpleText = Format ("Swap: (%s) [Drag the mouse to the name you wish to swap]",
      ARRAYOFCONST ((DrawingGrid->Cells[SwapFromX][SwapFromY])));
    Swapping =true;
  }
  else
    StatusBar->SimpleText = "";
}
//---------------------------------------------------------------------------

void __fastcall TMainForm::GridMouseMove(TObject *Sender,
      TShiftState Shift, int X, int Y)
{
  int CurrentX;
  int CurrentY;

  Grid->MouseToCell (X, Y, CurrentX, CurrentY);
  if (Swapping && CurrentX > 0 && CurrentY > 0 &&
      CurrentX < Grid->ColCount && CurrentY < Grid->RowCount &&
     (CurrentX != SwapFromX || CurrentY != SwapFromY))
    StatusBar->SimpleText = Format ("Swap: (%s) with (%s)",
      ARRAYOFCONST ((Grid->Cells[SwapFromX][SwapFromY], Grid->Cells[CurrentX][CurrentY])));
  else
    StatusBar->SimpleText = "";

}
//---------------------------------------------------------------------------

void __fastcall TMainForm::GridMouseUp(TObject *Sender,
      TMouseButton Button, TShiftState Shift, int X, int Y)
{
  String S;
  int CurrentX;
  int CurrentY;

  Grid->MouseToCell (X, Y, CurrentX, CurrentY);
  if (Swapping && CurrentX > 0 && CurrentY > 0 &&
      CurrentX < Grid->ColCount && CurrentY < Grid->RowCount &&
     (CurrentX != SwapFromX || CurrentY != SwapFromY))
  {
    S = Grid->Cells[CurrentX][CurrentY];
    Grid->Cells[CurrentX][CurrentY] = Grid->Cells[SwapFromX][SwapFromY];
    Grid->Cells[SwapFromX][SwapFromY] = S;
  }
  Swapping = false;
}



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Jose ParrotGraphics ExpertCommented:
Hummm.. with improvements and a touch of coding elegance!
Jose
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Kent OlsenData Warehouse Architect / DBAAuthor Commented:

Oops.    :)

It needs another improvement.  It doesn't differentiate between the left and right mouse buttons.


Do you really think this programming stuff is ever going to catch on?  ;)

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Jose ParrotGraphics ExpertCommented:
Yes, I think so. Conceptually, seems to be correct. Of course, turn this piece of code part of a commercial product will spend some extra effort, for exemple, in the differentiation of left/right button, as you have noticed (by accepting just mbLeft, for example) or adding columns/rows swapping (by accepting row and col zero).
When running your code I've changed DrawingGrid to Grid in the status bar text creation, as DrawingGrid didn't run in my environment (Builder 6).
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Kent OlsenData Warehouse Architect / DBAAuthor Commented:

Hi Jose,

DrawingGrid was the name of the object in my application.  That seemed confusing for this kind of post so I changed the name to "Grid".  Guess that I missed one.  :/

Other small improvements include checking the value of Swapping before calling MouseToCell(), etc.


Thanks again for a great suggestion!
Kent
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Jose ParrotGraphics ExpertCommented:
Anything else?
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Kent OlsenData Warehouse Architect / DBAAuthor Commented:

I've been out for the past week so I never got back to close this question.

Consider it closed and thanks again,
Kent
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