How to use the dgMultiSelect option in a TDBGrid

Problem/Question/Abstract:

How to use the dgMultiSelect option in a TDBGrid

Answer:

When you add [dgMultiSelect] to the Options property of a DBGrid, you give yourself the ability to select multiple records within the grid. The records you select are represented as bookmarks and are stored in the SelectedRows property. The SelectedRows property is an object of type TBookmarkList.

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, Grids, DBGrids, DB, DBTables;

type
  TForm1 = class(TForm)
    Table1: TTable;
    DBGrid1: TDBGrid;
    Count: TButton;
    Selected: TButton;
    Clear: TButton;
    Delete: TButton;
    Select: TButton;
    GetBookMark: TButton;
    Find: TButton;
    FreeBookmark: TButton;
    DataSource1: TDataSource;
    procedure CountClick(Sender: TObject);
    procedure SelectedClick(Sender: TObject);
    procedure ClearClick(Sender: TObject);
    procedure DeleteClick(Sender: TObject);
    procedure SelectClick(Sender: TObject);
    procedure GetBookMarkClick(Sender: TObject);
    procedure FindClick(Sender: TObject);
    procedure FreeBookmarkClick(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;
  Bookmark1: TBookmark;
  z: Integer;

implementation

{$R *.DFM}

{Example of the Count property}

procedure TForm1.CountClick(Sender: TObject);
begin
  if DBgrid1.SelectedRows.Count > 0 then
  begin
    showmessage(inttostr(DBgrid1.SelectedRows.Count));
  end;
end;

{Example of the CurrentRowSelected property}

procedure TForm1.SelectedClick(Sender: TObject);
begin
  if DBgrid1.SelectedRows.CurrentRowSelected then
    showmessage('Selected');
end;

{Example of the Clear Method}

procedure TForm1.ClearClick(Sender: TObject);
begin
  dbgrid1.SelectedRows.Clear;
end;

{Example of the Delete Method}

procedure TForm1.DeleteClick(Sender: TObject);
begin
  DBgrid1.SelectedRows.Delete;
end;

{This example iterates through the selected rows of the grid and displays
the second field of the dataset.
The Method DisableControls is used so that the DBGrid will not update when the
dataset is changed. The last position of the dataset is saved as a TBookmark.
The IndexOf method is called to check whether or not the bookmark is still existent.
The decision of using the IndexOf method rather than the Refresh method should be determined by the specific application.}

procedure TForm1.SelectClick(Sender: TObject);
var
  x: word;
  TempBookmark: TBookMark;
begin
  DBGrid1.Datasource.Dataset.DisableControls;
  with DBgrid1.SelectedRows do
    if Count > 0 then
    begin
      TempBookmark := DBGrid1.Datasource.Dataset.GetBookmark;
      for x := 0 to Count - 1 do
      begin
        if IndexOf(Items[x]) > -1 then
        begin
          DBGrid1.Datasource.Dataset.Bookmark := Items[x];
          showmessage(DBGrid1.Datasource.Dataset.Fields[1].AsString);
        end;
      end;
    end;
  DBGrid1.Datasource.Dataset.GotoBookmark(TempBookmark);
  DBGrid1.Datasource.Dataset.FreeBookmark(TempBookmark);
  DBGrid1.Datasource.Dataset.EnableControls;
end;

{This example allows you to set a bookmark and then search for the bookmarked record
within selected a record(s) within the DBGrid.}

{Sets a bookmark}

procedure TForm1.GetBookMarkClick(Sender: TObject);
begin
  Bookmark1 := DBGrid1.Datasource.Dataset.GetBookmark;
end;

{Frees the bookmark}

procedure TForm1.FreeBookmarkClick(Sender: TObject);
begin
  if assigned(Bookmark1) then
  begin
    DBGrid1.Datasource.Dataset.FreeBookmark(Bookmark1);
    Bookmark1 := nil;
  end;
end;

{Uses the Find method to locate the position of the bookmarked record within
the selected list in the DBGrid}

procedure TForm1.FindClick(Sender: TObject);
begin
  if assigned(Bookmark1) then
  begin
    if DBGrid1.SelectedRows.Find(TBookMarkStr(Bookmark1), z) then
      showmessage(inttostr(z));
  end;
end;

end.