「複数行にまたがるレコードを展開/折りたたむ」という要件を満たすには、単純に drawgrid を使用します。それを確認するには、drawgrid をフォームにドラッグしてから、次の Delphi 6 コードをプラグインします。基本的にオーバーヘッドなしで、5,000,000 件の複数行レコード (または必要な数) を折りたたんだり展開したりできます。これは単純な手法であり、多くのコードを必要とせず、驚くほどうまく機能します。
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms, Dialogs, Grids, StdCtrls;
type
TForm1 = class(TForm)
DrawGrid1: TDrawGrid;
procedure DrawGrid1DrawCell(Sender: TObject; ACol, ARow: Integer; Rect: TRect; State: TGridDrawState);
procedure DrawGrid1SelectCell(Sender: TObject; ACol, ARow: Integer; var CanSelect: Boolean);
procedure DrawGrid1TopLeftChanged(Sender: TObject);
procedure DrawGrid1DblClick(Sender: TObject);
procedure FormCreate(Sender: TObject);
private
procedure AdjustGrid;
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
// Display a large number of multi-line records that can be expanded or collapsed, using minimal overhead.
// LinesInThisRecord() and RecordContents() are faked; change them to return actual data.
const TOTALRECORDS = 5000000; // arbitrary; a production implementation would probably determine this at run time
// keep track of whether each record is expanded or collapsed
var isExpanded: packed array[1..TOTALRECORDS] of boolean; // initially all FALSE
function LinesInThisRecord(const RecNum: integer): integer;
begin // how many lines (rows) does the record need to display when expanded?
result := (RecNum mod 10) + 1; // make something up, so we don't have to use real data just for this demo
end;
function LinesDisplayedForRecord(const RecNum: integer): integer;
begin // how many lines (rows) of info are we currently displaying for the given record?
if isExpanded[RecNum] then result := LinesInThisRecord(RecNum) // all lines show when expanded
else result := 1; // show only 1 row when collapsed
end;
procedure GridRowToRecordAndLine(const RowNum: integer; var RecNum, LineNum: integer);
var LinesAbove: integer;
begin // for a given row number in the drawgrid, return the record and line numbers that appear in that row
RecNum := Form1.DrawGrid1.TopRow; // for simplicity, TopRow always displays the record with that same number
if RecNum > TOTALRECORDS then RecNum := 0; // avoid overflow
LinesAbove := 0;
while (RecNum > 0) and ((LinesDisplayedForRecord(RecNum) + LinesAbove) < (RowNum - Form1.DrawGrid1.TopRow + 1)) do
begin // accumulate the tally of lines in expanded or collapsed records until we reach the row of interest
inc(LinesAbove, LinesDisplayedForRecord(RecNum));
inc(RecNum); if RecNum > TOTALRECORDS then RecNum := 0; // avoid overflow
end;
LineNum := RowNum - Form1.DrawGrid1.TopRow + 1 - LinesAbove;
end;
function RecordContents(const RowNum: integer): string;
var RecNum, LineNum: integer;
begin // display the data that goes in the grid row. for now, fake it
GridRowToRecordAndLine(RowNum, RecNum, LineNum); // convert row number to record and line numbers
if RecNum = 0 then result := '' // out of range
else
begin
result := 'Record ' + IntToStr(RecNum);
if isExpanded[RecNum] then // show line counts too
result := result + ' line ' + IntToStr(LineNum) + ' of ' + IntToStr(LinesInThisRecord(RecNum));
end;
end;
procedure TForm1.AdjustGrid;
begin // don't allow scrolling past last record
if DrawGrid1.TopRow > TOTALRECORDS then DrawGrid1.TopRow := TOTALRECORDS;
if RecordContents(DrawGrid1.Selection.Top) = '' then // move selection back on to a valid cell
DrawGrid1.Selection := TGridRect(Rect(0, TOTALRECORDS, 0, TOTALRECORDS));
DrawGrid1.Refresh;
end;
procedure TForm1.DrawGrid1DrawCell(Sender: TObject; ACol, ARow: Integer; Rect: TRect; State: TGridDrawState);
var s: string;
begin // time to draw one of the grid cells
if ARow = 0 then s := 'Data' // we're in the top row, get the heading for the column
else s := RecordContents(ARow); // painting a record, get the data for this cell from the appropriate record
// draw the data in the cell
ExtTextOut(DrawGrid1.Canvas.Handle, Rect.Left, Rect.Top, ETO_CLIPPED or ETO_OPAQUE, @Rect, pchar(s), length(s), nil);
end;
procedure TForm1.DrawGrid1SelectCell(Sender: TObject; ACol, ARow: Integer; var CanSelect: Boolean);
var RecNum, ignore: integer;
begin
GridRowToRecordAndLine(ARow, RecNum, ignore); // convert selected row number to record number
CanSelect := RecNum <> 0; // don't select unoccupied rows
end;
procedure TForm1.DrawGrid1TopLeftChanged(Sender: TObject);
begin
AdjustGrid; // keep last page looking good
end;
procedure TForm1.DrawGrid1DblClick(Sender: TObject);
var RecNum, ignore, delta: integer;
begin // expand or collapse the currently selected record
GridRowToRecordAndLine(DrawGrid1.Selection.Top, RecNum, ignore); // convert selected row number to record number
isExpanded[RecNum] := not isExpanded[RecNum]; // mark record as expanded or collapsed; subsequent records might change their position in the grid
delta := LinesInThisRecord(RecNum) - 1; // amount we grew or shrank (-1 since record already occupied 1 line)
if isExpanded[RecNum] then // just grew
else delta := -delta; // just shrank
DrawGrid1.RowCount := DrawGrid1.RowCount + delta; // keep rowcount in sync
AdjustGrid; // keep last page looking good
end;
procedure TForm1.FormCreate(Sender: TObject);
begin
Caption := FormatFloat('#,##0 records', TOTALRECORDS);
DrawGrid1.RowCount := TOTALRECORDS + 1; // +1 for column heading
DrawGrid1.ColCount := 1;
DrawGrid1.DefaultColWidth := 300; // arbitrary
DrawGrid1.DefaultRowHeight := 12; // arbitrary
DrawGrid1.Options := DrawGrid1.Options - [goVertLine, goHorzLine, goRangeSelect] + [goDrawFocusSelected, goThumbTracking]; // change some defaults
end;
end.