轻松实现DBGrid的多表头

用法：
  设置DBGrid的Column的Caption属性
  例如：Column1的Caption为111|222
        Column2的Caption为111|333
        那么Column1和Column2公用一个表头111

unit ADBGrid;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  Grids, DBGrids, Math;

type
  TADBGrid = class(TDBGrid)
  private
    { Private declarations }
    //兄弟列子标题,当前列子标题
    BrerLayerTitles, CurLayerTitles: TStringList;
    SaveFont: TFont;
    //根据当前数据列号和表头的层号获取表头的区域
    function TitleLayerRect(LayerTitles: TStrings; TitleRect: TRect; LayerID, ACol: Integer): TRect;
    //解出当前数据列标题为子标题并返回标题层数(子标题数)
    function ExtractSubTitle(LayerTitles: TStrings; ACol: Integer): Integer;
  protected
    { Protected declarations }
    procedure DrawCell(ACol, ARow: Longint; ARect: TRect; AState: TGridDrawState); override;
    procedure Paint; override;
  public
    { Public declarations }
    constructor Create(AOwner: TComponent); override;
    destructor Destroy; override;
  published
    { Published declarations }
  end;

procedure Register;

implementation

procedure Register;
begin
  RegisterComponents('Samples', [TADBGrid]);
end;

constructor TADBGrid.Create(AOwner: TComponent);
begin
  inherited;
  BrerLayerTitles := TStringList.Create;
  curLayerTitles := TStringList.Create;
  SaveFont := TFont.Create;
end;

destructor TADBGrid.Destroy;
begin
  BrerLayerTitles.Free;
  curLayerTitles.Free;
  SaveFont.Free;
  inherited;
end;

procedure TADBGrid.DrawCell(ACol, ARow: Integer; ARect: TRect;
  AState: TGridDrawState);
var
  SubTitleRT, CaptionRt, IndicatorRT: TRect;
  Column: TColumn;
  SubTitle: string;
  i: Integer;
begin
  if (ARow = 0) and (ACol > 0) then
  begin
    ExtractSubTitle(curLayerTitles, RawToDataColumn(ACol));
    for i := 0 to curLayerTitles.Count - 1 do
    begin
      SubTitleRT := TitleLayerRect(curLayerTitles, ARect, i, RawToDataColumn(ACol));
      CaptionRt := SubTitleRT;
      Canvas.Brush.Color := FixedColor;
      Canvas.FillRect(SubTitleRT);

      DrawEdge(Canvas.Handle, SubTitleRT, BDR_RAISEDINNER, BF_TOPLEFT);
      if i <> CurLayerTitles.Count - 1 then
      begin
        DrawEdge(Canvas.Handle, SubTitleRT, BDR_RAISEDOUTER, BF_BOTTOM);
        Dec(SubTitleRT.Bottom, 2);
      end else Dec(SubTitleRT.Bottom, 1);
      Canvas.Pen.Color := clWhite;
      Dec(SubTitleRT.Right, 1);
      Canvas.MoveTo(SubTitleRT.Right, SubTitleRT.Top);
      Canvas.LineTo(SubTitleRT.Right, SubTitleRT.Bottom);
      Canvas.LineTo(SubTitleRT.Left, SubTitleRT.Bottom);
      Column := Columns[RawToDataColumn(ACol)];
      SubTitle := '';
      if Assigned(Column) then
      begin
        SubTitle := CurLayerTitles[i];
        SaveFont.Assign(Canvas.Font);
        Canvas.Font.Assign(TitleFont);
        try
          InflateRect(SubTitleRT, -1, -1);
          DrawText(Canvas.Handle, PChar(SubTitle), Length(SubTitle),
            SubTitleRT, DT_CENTER or DT_SINGLELINE or DT_VCENTER);
        finally
          Canvas.Font.Assign(SaveFont);
        end;
      end;
    end;
    if dgIndicator in Options then
    begin
      IndicatorRT := Rect(0, 0, IndicatorWidth + 1, RowHeights[0]);
      Canvas.FillRect(IndicatorRT);