demo.~pas

计算字段实例,可以提取主要的字段加以计算

unit demo;

interface

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

type
  TForm1 = class(TForm)
    DBGrid1: TDBGrid;
    Label1: TLabel;
    Edit1: TEdit;
    Label2: TLabel;
    Edit2: TEdit;
    Label3: TLabel;
    Edit3: TEdit;
    Label4: TLabel;
    Edit4: TEdit;
    Label5: TLabel;
    Edit5: TEdit;
    Label6: TLabel;
    Edit6: TEdit;
    Button1: TButton;
    Table1: TTable;
    DataSource1: TDataSource;
    Table1Name: TStringField;
    Table1Capital: TStringField;
    Table1Continent: TStringField;
    Table1Area: TFloatField;
    Table1Population: TFloatField;
    Table1ratio: TFloatField;
    procedure FormActivate(Sender: TObject);
    procedure Table1BeforeScroll(DataSet: TDataSet);
    procedure Table1AfterScroll(DataSet: TDataSet);
    procedure Button1Click(Sender: TObject);
    procedure Table1CalcFields(DataSet: TDataSet);
  private
    { Private declarations }
  public
    { Public declarations }
    procedure initiate;
    procedure LoadFromTable;
    procedure SaveToTable;
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.FormActivate(Sender: TObject);
begin
      initiate;
      Table1.Active:=true;
      LoadFromTable;
end;
procedure TForm1.initiate;
begin
      Edit1.text:='';
      Edit2.text:='';
      Edit3.text:='';
      Edit4.text:='1';
      Edit5.text:='0';
      Edit6.text:='0';
      Edit6.Enabled:=false;
      Table1Name.DisplayLabel:='国家名';
      Table1capital.DisplayLabel:='首都名';
      Table1Continent.DisplayLabel:='所在州';
      Table1Area.DisplayLabel:='面积';
      Table1Population.DisplayLabel:='人口数';
      Table1Ratio.DisplayLabel:='单位面积人口';
end;
procedure TForm1.LoadFromTable;
begin
      Edit1.Text:=Table1Name.AsString;
      Edit2.Text:=Table1Capital.AsString;
      Edit3.Text:=Table1Continent.AsString;
      Edit4.Text:=IntToStr(Table1Area.AsInteger);
      Edit5.Text:=IntToStr(Table1Population.AsInteger);
      Edit6.Text:=FloatToStr(Table1Ratio.AsFloat);
end;
procedure TForm1.SaveToTable;
begin
      Table1.Edit; 
      Table1Name.AsString:=Edit1.Text;
      Table1Capital.AsString:=Edit2.Text;
      Table1Continent.AsString:=Edit3.Text;
      Table1Area.AsInteger:=StrToInt(Edit4.Text);
      Table1Population.AsInteger:=StrToInt(Edit5.Text);
      Table1.post;
end;
procedure TForm1.Table1BeforeScroll(DataSet: TDataSet);
begin
      SaveToTable;
end;

procedure TForm1.Table1AfterScroll(DataSet: TDataSet);
begin
    LoadFromTable;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
    Table1.active:=false;
    close;
end;

procedure TForm1.Table1CalcFields(DataSet: TDataSet);
begin
      Table1Ratio.AsFloat:=Table1Population.AsInteger/Table1Area.AsInteger;
end;

end.