用DLL实现插件的简单演示

这是DLL的代码

library MyDll;

uses
  SysUtils,
  Dialogs,
  Classes;

procedure ShowInfo(info:PChar);stdcall;
begin
  ShowMessage('您选择了【'+info+'】');
end;

function GetCaption:Pchar;
begin
  Result := '中国';
end;

exports ShowInfo,        
        GetCaption;

{$R *.res}

begin
end.

这是调用窗体的代码
本例只使用了一个DLL，所以当有多个DLL时，需要循环DLL所在目录，依次加载DLL

unit Main;

interface

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

type
  TShowInfo = procedure (info:PChar);stdcall;
  TGetCaption = function : PChar;stdcall;


  TForm1 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    MainMenu1: TMainMenu;
    Image1: TImage;
    procedure Button2Click(Sender: TObject);  private
    { Private declarations }
    FHandel : THandle;     //DLL句柄
    FProAddress: Pointer;  //DLL中ShowInfo的地址
    showinfo: TShowInfo;   //为动态加载DLL而设
    procedure LoadPlusIn;  //加载插件（DLL）
    procedure ItemClick(Sender: TObject);   //自定义菜单点击事件
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.Button2Click(Sender: TObject);
begin
  LoadPlusIn;
end;

procedure TForm1.ItemClick(Sender: TObject);
begin
  @showinfo := FProAddress;     //取地址
  if @showinfo <> nil then
    showinfo(PWideChar(TMenuItem(Sender).Caption));  //执行DLL中的ShowInfo
end;

procedure TForm1.LoadPlusIn;
var
  getcaption: TGetCaption;
  item : TMenuItem;
begin
  FHandel := LoadLibrary('MyDll.dll');   //加载
  if FHandel = 0 then
  begin
    ShowMessage('加载失败！');
    Exit;
  end
  else
  begin
    @getcaption := GetProcAddress(FHandel,'GetCaption');    //取DLL中GetCaption地址
    if @getcaption <> nil then
    begin
      item := TMenuItem.Create(MainMenu1);    //创建一个菜单
      item.Caption := getcaption;             //取Caption，即调用DLL中的GetCaption
      FProAddress := GetProcAddress(FHandel,'ShowInfo');  //取得DLL中ShowInfo的地址
      item.OnClick := ItemClick;              //赋予菜单项的点击事件
      MainMenu1.Items.Add(item);              //添加到主菜单
    end;

  end;
end;

end.