Here is how to achieve shift-click (contiguous) select on TDBGrid
lazarus / 16-Databases

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grandehombre · 2013-08-11 12:45

Code: [Select]{
Usage:
in the form that needs this functionality, add

var
    previousGridBookmark: TBookmark;

...
...
...


procedure TfrmTest.DBGrid1CellClick(Column: TColumn);
begin
        DBGridShiftSelect(DBGrid1, previousGridBookmark);

  // save last selected bookmark
  previousGridBookmark := DBGrid1.DataSource.DataSet.GetBookmark;
end;


// Don't forget to clear the above bookmark when you clear or re-
populate the grid
//
// Example code
//if assigned(previousGridBookmark) then begin
//       
DBGrid1.DataSource.DataSet.FreeBookmark(previousGridBookmark);
//        previousGridBookmark := nil;
//    end;


}

Add this code to a unit of its own (or in the form itself, though  it
would be best on its own, so it can be reused!)


// Allow shift-Ckick marking of a contiguous block
procedure DBGridShiftSelect(Sender: TObject; existingBookmarks:
TBookmark);
var
        curPos: TBookmark;
        limiter: integer;
        grid: TDBGrid;
        dSet: TDataSet;
        rFrom, rTo, rTmp: integer;
begin
        grid := (Sender as TDBGrid);
        dSet := grid.DataSource.DataSet;

        // Get the current position (bookmark) and record number (the
row we shift-clicked on)
        curPos := dSet.GetBookmark;
        rTo := dSet.RecNo;

        dSet.DisableControls;
        try
        // dummy loop that allows multiple exits to a single point
                repeat
                        if not (ssShift in GetKeyShiftState) then
begin
                                exit;
                        end;

                        if (existingBookmarks = nil) then begin
                                exit;
                        end;

                        // go to the last bookmark before we shift-
clicked
                        dSet.GotoBookmark(existingBookmarks);
                        rFrom := dSet.RecNo;

                        if rTo = rFrom then begin
                                exit;
                        end;

                        // we want to only mark moving forward, so if
need be, swap the bookmarks
                        if rTo < rFrom then begin
                                rTmp := rTo;
                                rTo := rFrom;
                                rFrom := rTmp;
                                grid.SelectedRows.CurrentRowSelected
:= True;
                                dSet.GotoBookmark(curPos);
                        end;

                        // stop after marking 255 rows (just in case
recNo is not a reliable method of doing this.
                        // This is probably no longer an issue but it
doesn't hurt to leave it here :-)
                        limiter := 255;
                        repeat
                                // highlight current row
                                grid.SelectedRows.CurrentRowSelected
:= True;
                                dset.Next;

                                rFrom := dSet.recNo;
                                limiter := limiter - 1;

                                // keep going until we reach the
shift-clicked row
                        until (limiter < 0) or (rFrom = rTo);
                until true;
        finally
                dSet.FreeBookmark(curPos);
                dSet.EnableControls;
        end;
end;


UPDATE: Added note on clearing the bookmark when clearing/repopulating
the grid

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rfwoolf · 2020-07-13 00:34

Well done!
I just tested this and it works pretty well.
One thing that needs improvement:
If you want to use shift-click twice:

Example:
1. You select row 10.
2. You use shift-click to select row 20.
  Rows 10-20 are now selected
3. You use shift-click to select row 30.
  Expected behaviour:
  It should select rows 10-30.
  Actual behaviour:
  It selects rows 20-30

I made some minor tweaks to the code, but essentially it's the same as
you wrote:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i //Declare a
global variable //Used for special function on TDBGrids: the ability
to use Shift to select multiple rows//(See DBGridShiftSelect)var 
DBGridPriorBookmark : TBookmark; //Don't forget to clear the above
bookmark when you clear or re-populate the grid//Example, place this
in Dataset.AfterRefresh://begin//  if assigned(DBGridPriorBookmark)
then//  begin//    DataSet.FreeBookmark(DBGridPriorBookmark);//  
 DBGridPriorBookmark := nil;//  end;//end; //Add this code to a unit
of its own (or in the form itself, though it would be best on its own,
so it can be reused!)// In a DBGrid, allow Shift-Click marking of a
contiguous blockprocedure DBGridShiftSelect(Sender: TObject;
existingBookmarks: TBookmark);var  curPos: TBookmark;  limiter:
integer;  aDBGrid: TDBGrid;  aDataset: TDataSet;  iFrom,  iTo,  iTmp:
integer;begin   //Validation  if not (ssShift in GetKeyShiftState)
then    exit;   if (existingBookmarks = nil) then    exit;  
//Initiliasation  aDBGrid := (Sender as TDBGrid);  aDataset :=
aDBGrid.DataSource.DataSet;   // Get the current position (bookmark)
and record number (the row we shift-clicked on)  curPos :=
aDataset.GetBookmark;  iTo := aDataset.RecNo;  
aDataset.DisableControls;  try    //dummy loop that allows multiple
exits to a single point    repeat      //go to the last bookmark
before we shift-clicked     
aDataset.GotoBookmark(existingBookmarks);      iFrom :=
aDataset.RecNo;       if iTo = iFrom then        exit;       //we want
to only select moving forward, so if need be, swap the bookmarks     
if iTo < iFrom then      begin        iTmp := iTo;        iTo :=
iFrom;        iFrom := iTmp;       
aDBGrid.SelectedRows.CurrentRowSelected := True;       
aDataset.GotoBookmark(curPos);      end;       //Stop after marking
255 rows (just in case recNo is not a reliable method of doing this. 
   //This is probably no longer an issue but it doesn't hurt to leave
it here :-)      limiter := 255;       repeat        //highlight
current row        aDBGrid.SelectedRows.CurrentRowSelected := True;  
    aDataset.Next;         iFrom := aDataset.recNo;        limiter :=
limiter - 1;         //keep going until we reach the shift-clicked
row      until        (limiter < 0) or (iFrom = iTo);    until     
true;  finally    aDataset.FreeBookmark(curPos);   
aDataset.EnableControls;  end;end; 
//Add this to the DBGrid's onCellClick method:
procedure TfrmTest.DBGrid1CellClick(Column: TColumn);
begin
  DBGridShiftSelect(DBGrid1, DBGridPriorBookmark);

  // save last selected bookmark
  DBGridPriorBookmark := DBGrid1.DataSource.DataSet.GetBookmark;
end;

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emilt · 2020-07-15 14:27

That is very nice, but it made me wonder - is there any special reason
why the shift+click functionality is not built-in into the TDBGrid
component by default? After all, you can use shift+arrows to do the
same with the keyboard, why not with the mouse too?