mainfrm.pas

《Delphi 7经典问题解析》源代码 第一到七章 基础篇源程序 应用篇源程序

unit Mainfrm;

interface

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

type
  TfrmMain = class(TForm)
    Database1: TDatabase;
    Query1: TQuery;
    DataSource1: TDataSource;
    Database2: TDatabase;
    Query2: TQuery;
    DataSource2: TDataSource;
    btnQuery: TSpeedButton;
    DBGrid1: TDBGrid;
    DBGrid2: TDBGrid;
    Session2: TSession;
    Session1: TSession;
    procedure btnQueryClick(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

//后台查询数据库的线程类
TQueryThread = class(TThread)
  private
    FSession: TSession;
    FDatabase: TDataBase;
    FQuery: TQuery;
    FDatasource: TDatasource;
    FQueryException: Exception;
    procedure ConnectDataSource;
    procedure ShowQryError;
  protected
    procedure Execute; override;
  public
    constructor Create(Session: TSession; DataBase:
      TDatabase; Query: TQuery; DataSource: TDataSource);virtual;
  end;


var
  frmMain: TfrmMain;

implementation

{$R *.dfm}
//TQueryThread的实现

constructor TQueryThread.Create(Session: TSession; DataBase:
  TDatabase; Query: TQuery; Datasource: TDataSource);
begin
  inherited Create(False);    //以立即执行方式创建线程
  //将传进来的数据库的相关对象赋给私有变量
  FSession := Session;
  FDatabase := DataBase;
  FQuery := Query;
  FDataSource := Datasource;

  FreeOnTerminate := True;   //  //当线程执行完，终止线程
end;


procedure TQueryThread.Execute;
begin
  try
    FQuery.Open;
    Synchronize(ConnectDataSource);
  except
    FQueryException := ExceptObject as Exception;
    Synchronize(ShowQryError);
  end;
end;

procedure TQueryThread.ConnectDataSource;
begin
  FDataSource.DataSet := FQuery;  //连接DataSource到数据集Query上
end;

procedure TQueryThread.ShowQryError;
begin
  Application.ShowException(FQueryException);
end;

procedure RunBackgroundQuery(Session: TSession; DataBase:
TDataBase;Query: TQuery; DataSource:TDataSource);
begin
  TQueryThread.Create(Session, Database, Query, DataSource);
end;

//TfrmMain实现

procedure TfrmMain.btnQueryClick(Sender: TObject);
begin
  RunBackgroundQuery(Session1, DataBase1, Query1,Datasource1);
  RunBackgroundQuery(Session2, DataBase2, Query2,Datasource2);

end;

end.