用Delphi开发数据库应用程序的常用方式

用Delphi开发数据库应用，一般会涉及到闪屏（Splash）、登录窗口、主数据模块（或主数据库连接）以及主窗口。通常在项目文件中，splash窗口显示过，一些需要加载的资源、窗口加载过后，Application.Run之前，进行用户登录。
//测试CSDN博客对DELPHI代码的支持
program TEST;
uses
Forms,
Windows,
MainF in 'MainF.pas' {frmMain},
SplashF in 'SplashF.pas' {frmSplash},
mainDM in 'mainDM.pas' {dmMain: TDataModule},
LoginF in 'LoginF.pas' {frmLogin};
{$R *.RES}
var
frmMain: TfrmMain;
dmMain: TdmMain;
begin
Application.Initialize;
//显示封面
SplashF.Show;
try
//创建需要的资源
Application.CreateForm(TdmMain, dmMain);
Application.CreateForm(TfrmMain, frmMain);
//...
finally
SplashF.Close;
end;
if LoginF.Login() then //呼叫登录窗口
Application.Run;
end.

此时，可能用到的数据连接已经建立起来了，登录就可以进系统。
LoginF.pas
unit LoginF;
interface
uses
Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
ExtCtrls, StdCtrls, Buttons;
type
TfrmLogin = class(TForm)
pnl1: TPanel;
edUserName: TEdit;
lblUserName: TLabel;
edPasswd: TEdit;
lblPasswd: TLabel;
btnOK: TBitBtn;
btnCancel: TBitBtn;
procedure FormCreate(Sender: TObject);
procedure btnOKClick(Sender: TObject);
private
FTryTimes: Integer;
function CheckUserInfo(AUserName, APassword: string): Boolean;
public
end;
function Login: Boolean; //登录函数
implementation
{$R *.DFM}
function Login: Boolean;
begin
//动态创建登录窗口
with TfrmLogin.Create(nil) do
begin
//只有返回OK的时候认为登录成功
Result := ShowModal() = mrOk;
Free;
end;
end;
function TfrmLogin.CheckUserInfo(AUserName, APassword: string): Boolean;
begin
//验证
Result := (AUserName = 'lihd' ) and (APassword = 'P@ssw0rd');
end;
procedure TfrmLogin.FormCreate(Sender: TObject);
begin
//尝试登录的次数，初始化为0
FTryTimes := 0;
end;
procedure TfrmLogin.btnOKClick