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2976:TDBGrid and Multi-Selecting Records

KEYWORDS: Database, TDBGrid, multi-select, dgMultiSelect, SelectedRows AREA: D

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.  The properties and methods are
described below.

// property SelectedRows: TBookmarkList read FBookmarks;

//   TBookmarkList = class
//   public

     {* The Clear method will free all the selected records
        within the DBGrid *}
     // procedure Clear;

    {* The Delete method will delete all the selected rows
       from the dataset *}
    // procedure Delete;

    {* The Find method determines whether a bookmark is
       in the selected list. *}
    // function  Find(const Item: TBookmarkStr;
    //      var Index: Integer): Boolean;

    {* The IndexOf method returns the index of the
       bookmark within the Items property. *}
    // function IndexOf(const Item: TBookmarkStr): Integer;

    {* The Refresh method returns a boolean value to notify
       whether any orphans were dropped (deleted) during the
       time the record has been selected in the grid.  The
       refresh method can be used to update the selected list
       to minimize the possibility of accessing a deleted
       record. *}
    // function  Refresh: Boolean;  True = orphans found

    {* The Count property returns the number of currently
       selected items in the DBGrid *}
    // property Count: Integer read GetCount;

    {* The CurrentRowSelected property returns a boolean
       value and determines whether the current row is
       selected or not. *}
    // property CurrentRowSelected: Boolean
    //      read GetCurrentRowSelected
    //      write SetCurrentRowSelected;

    {* The Items property is a TStringList of
       TBookmarkStr *}
    // property Items[Index: Integer]: TBookmarkStr
    //      read GetItem; default;

//  end;

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;
    DBGrid1.Datasource.Dataset.GotoBookmark(TempBookmark);
    DBGrid1.Datasource.Dataset.FreeBookmark(TempBookmark);
  end;
  DBGrid1.Datasource.Dataset.EnableControls;
end;

{*
This example allows you to set a bookmark and
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.

        TI

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