Dll学习一_Dll 创建并动态引用窗体且释放窗体Demo

1、新建Dll工程

2、Dll工程全部代码

library SubMain;

{ Important note about DLL memory management: ShareMem must be the
  first unit in your library's USES clause AND your project's (select
  Project-View Source) USES clause if your DLL exports any procedures or
  functions that pass strings as parameters or function results. This
  applies to all strings passed to and from your DLL--even those that
  are nested in records and classes. ShareMem is the interface unit to
  the BORLNDMM.DLL shared memory manager, which must be deployed along
  with your DLL. To avoid using BORLNDMM.DLL, pass string information
  using PChar or ShortString parameters. }

uses
  SysUtils, Forms,
  Classes, Windows, Dialogs,
  SubMain_Unit in 'SubMain_Unit.pas' {Frm_SubMain};

var
  AppHnd: Thandle;//应用程序的句柄变量
  AppScr: TScreen;//应用程序的环境变量
{$R *.res}

procedure DllEntryPoint(dwReason: DWord);
begin

  case dwReason of
    DLL_PROCESS_ATTACH:
    begin
      AppHnd := Application.Handle;//备份Exe句柄
      AppScr := Screen;//备份Exe环境
    end;
    DLL_THREAD_ATTACH: ShowMessage('Create Thread'); //Dll文件中最好用Messagebox，ShowMessage部分环境中容易抽风
    DLL_THREAD_DETACH: ShowMessage('Free Thread'); //Dll文件中最好用Messagebox，ShowMessage部分环境中容易抽风 
    DLL_PROCESS_DETACH:
    begin
      if Frm_SubMain <> nil then FreeAndNil(Frm_SubMain);//防止Dll窗体未释放干净
      Application.Handle := AppHnd;      //恢复Exe句柄
      Screen := AppScr;//恢复Exe环境
    end;
  end;
end;

exports
  CreateFrm,DropFrm;//输出函数接口

begin
  DllProc := @DllEntryPoint;
  DllEntryPoint(DLL_PROCESS_ATTACH);
end.

3、SubMain_Unit.pas源码

unit SubMain_Unit;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, FyFun_Unit;

type
  TFrm_SubMain = class(TForm)
    procedure FormClose(Sender: TObject; var Action: TCloseAction);
    procedure FormDestroy(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;
  procedure CreateFrm(AppHnd: THandle);export;stdcall;//接口函数声明
  procedure DropFrm; export;stdcall;//接口函数声明
var
  Frm_SubMain: TFrm_SubMain;

implementation

{$R *.dfm}
procedure CreateFrm(AppHnd: THandle);//窗体创建函数
begin
  Application.Handle := AppHnd;

  if not Assigned(Frm_SubMain) then
    Frm_SubMain := TFrm_SubMain.Create(Application);

  Frm_SubMain.Show;
end;

procedure DropFrm;//窗体释放函数
begin
  if Frm_SubMain <> nil then
    FreeAndNil(Frm_SubMain);
end;
procedure TFrm_SubMain.FormClose(Sender: TObject; var Action: TCloseAction);
begin
  Action := caFree;//dll窗体关闭自动释放
end;

procedure TFrm_SubMain.FormDestroy(Sender: TObject);
begin
  Frm_SubMain := nil;//dll窗体关闭自动释放
end;

end.

4、调用文件Main.pas代码

unit Main_Unit;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TCreateFrm = procedure(AppHnd: THandle); stdcall;
  TDropFrm = procedure; stdcall;
  TFrm_Main = class(TForm)
    Btn_1: TButton;
    Btn_2: TButton;
    Btn_3: TButton;
    Btn_4: TButton;
    procedure Btn_1Click(Sender: TObject);
    procedure Btn_2Click(Sender: TObject);
    procedure Btn_3Click(Sender: TObject);
    procedure Btn_4Click(Sender: TObject);
  private
    LibHandle: THandle;
    FormRef: LongInt;
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Frm_Main: TFrm_Main;

implementation

{$R *.dfm}

procedure TFrm_Main.Btn_1Click(Sender: TObject);		//动态加载Dll文件
begin
  if LibHandle = 0 then
  begin
    LibHandle := SafeLoadLibrary('SubMain.dll');
    if LibHandle = 0 then
      raise Exception.Create('Not Found Dll File')
    else
      ShowMessage('Dll Loaded');
  end;
end;

procedure TFrm_Main.Btn_2Click(Sender: TObject);		//释放Dll文件
begin
  if LibHandle > 0 then
  begin
    FreeLibrary(LibHandle);
    LibHandle := 0;
    ShowMessage('Dll UnLoaded');
  end;
end;

procedure TFrm_Main.Btn_3Click(Sender: TObject);		//读取Dll文件窗体并显示
var
  CreateFrm: TCreateFrm;
begin
  if LibHandle = 0 then
    raise Exception.Create('Place Load Dll File First');

  @CreateFrm := GetProcAddress(LibHandle,PChar('CreateFrm'));
  if @CreateFrm = nil then
    raise Exception.Create('Function Error');

  CreateFrm(Application.Handle);
end;

procedure TFrm_Main.Btn_4Click(Sender: TObject);		//释放Dll窗体
var
  DropFrm: TDropFrm;
begin
  @DropFrm := GetProcAddress(LibHandle,PChar('DropFrm'));
  if @DropFrm = nil then
    raise Exception.Create('Function Error');

  DropFrm;
end;

end.