我用Delphi写了一个DLL封装一个登录窗口老出问题。知道的高手进来瞅瞅

Question

library Project1;
uses
  SysUtils,
  Classes,
  Controls,
  Forms,
  Windows,
  Unit1 in 'Unit1.pas' {FrmLogin};//登录对话框;var
  Myconn:string; //定义公共变量，数据库连接字符串{$R *.res}Procedure SetConn(Conn:Pchar);Stdcall;
begin
  Myconn:=StrPas(Conn);
end;function CheckPass(Apphandle:THandle;var opID:pchar;var opName:pchar;var opUsername:pchar):Boolean;Stdcall;
var
  FrmLogin:TfrmLogin;
  ResultModal:integer;//窗体返回值
begin
  opID:=pChar(''); opName:=pChar('');opUsername:=pchar('');Result:=false;
  if Myconn='' Then  exit;
  Application.Handle:=Apphandle;
  FrmLogin:=TFrmLogin.Create(nil);
  try
    FrmLogin.ADOQ.ConnectionString:=Myconn;
    ResultModal:=FrmLogin.ShowModal;
    if ResultModal = mrok then
    begin
      opID:=PChar(FrmLogin.SopID);
      opName:=pchar(FrmLogin.Sopname);
      opUsername:=pchar(FrmLogin.sopusername);
      Result:=true;
    end;
  finally
    FrmLogin.Free;
    Application.Handle:=0;
  end;
end;
exports
  SetConn,CheckPass;
begin
end.

Answer 1

在你的FrmLogin的单元的最后代码的地方end;与end.之间加上.....
end;
initialization
  CoInitialize(nil);finalization
  CoUninitialize;
end.

Answer 2

FrmLogin:=TFrmLogin.Create(nil); 
  try 
    FrmLogin.ADOQ.ConnectionString:=Myconn; 
    ResultModal:=FrmLogin.ShowModal; 
    if ResultModal = mrok then 
    begin 
      opID:=PChar(FrmLogin.SopID); 
      opName:=pchar(FrmLogin.Sopname); 
      opUsername:=pchar(FrmLogin.sopusername); 
      Result:=true; 
    end; 
  finally 
    FrmLogin.Free;  <-- FrmLogin被释放了，opUsername，opName，opID的操作会产生不可预料的结果
    Application.Handle:=0; 
  end; 

Answer 3

function CheckPass(Apphandle:THandle;var opID:pchar;var opName:pchar;var opUsername:pchar;Conn:Pchar):Boolean;Stdcall;
var
  FrmLogin:TfrmLogin;
  ResultModal:integer;//窗体返回值
begin
  opID:=pChar('');
  opName:=pChar('');
  opUsername:=pchar('');
  Result:=false;  if Conn='' Then  exit;
  Application.Handle:=Apphandle;
  FrmLogin:=TFrmLogin.Create(nil);
  try
    FrmLogin.ADOQ.ConnectionString:=Conn;
    ResultModal:=FrmLogin.ShowModal;
    if ResultModal = mrok then
    begin
      opID:=PChar(FrmLogin.SopID);
      opName:=pchar(FrmLogin.Sopname);
      opUsername:=pchar(FrmLogin.sopusername);
      Result:=true;
    end;
  finally
    FrmLogin.Free;
    Application.Handle:=0;
  end;
end;
exports
  CheckPass;
begin
end.

Answer 4

//DLL部分
library Project1;
uses
  SysUtils,
  Classes,
  Forms,
  Controls,  Unit1 in 'Unit1.pas' {FrmLogin};var
  Myconn:string;
{$R *.res}
Procedure SetConn(Conn:Pchar);Stdcall;
begin
  Myconn:=StrPas(Conn);
end;function CheckPass(Apphandle:THandle;var opID:pchar;var opName:pchar;var opUsername:pchar):Boolean;Stdcall;
var
  FrmLogin:TfrmLogin;
  ResultModal:integer;//窗体返回值
begin
  Result:=false;
  if Myconn='' Then  exit;
  Application.Handle:=Apphandle;
  FrmLogin:=TFrmLogin.Create(nil);
  try
    FrmLogin.ADOQ.ConnectionString:=Myconn;
    ResultModal:=FrmLogin.ShowModal;
    if ResultModal = mrok then
    begin
       StrPCopy(opID,FrmLogin.SopID.Text);
       StrPCopy(opName,FrmLogin.Sopname.Text);
       StrPCopy(opUsername,FrmLogin.sopusername.Text);
       Result:=true;
    end;
  finally
    FrmLogin.Free;
    Application.Handle:=0;
  end; 
end;
exports 
  SetConn,CheckPass; begin
end.
//什么时候真正用到ADO操作，那么要及时进入套间，来初始化一下其工作环境
//调用程序
type
  TSetConn=procedure (Conn:Pchar);stdcall;
  TCheckPass=function(Apphandle:THandle;var opID:pchar;var opName:pchar;var opUsername:pchar):boolean;stdcall;procedure TForm1.GetLogonForm;
var
  DllHnd: THandle;
  SetConn: TSetConn;
  CheckPass:TCheckPass;
  opID,opName,opUsername: PChar;
  size:Integer;
begin
  size:=255;
  DllHnd := LoadLibrary(PChar('project1.dll'));
  try
    if (DllHnd <> 0) then
    begin
      @SetConn :=GetProcAddress(DllHnd, 'SetConn');
      if (@SetConn<>nil) then
      begin
        SetConn('Provider=SQLOLEDB.1;Integrated Security=SSPI;Persist Security Info=False;Initial Catalog=CSDNTest;Data Source=.');
        @CheckPass :=GetProcAddress(DllHnd, 'CheckPass');
        if (@CheckPass<>nil) then
        begin
          GetMem(opID,size);
          GetMem(opName, size);
          GetMem(opUsername,Size);
          try
            if CheckPass(Application.Handle,opID,opName,opUsername) then
            showmessage('ok');          finally
            FreeMem(opID);
            FreeMem(opName);
            FreeMem(opUsername);
          end;
        end;
      end
      else
      begin
        application.MessageBox(PChar('DLL加载出错，DLL可能不存在！'), PChar('错误'),
          MB_ICONWARNING or MB_OK);
      end;
    end;
  finally
    FreeLibrary(DllHnd);
  end;
end;