调用外部 DLL 中的函数(2. 晚绑定)

unit Unit1;

interface

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

type
  //晚绑定，也就是动态调用外部函数主要用以下三个命令：
  //LoadLibrary：获取 DLL
  //GetProcAddress：获取函数
  //FreeLibrary：释放

  //定义一个过程类型，参数要和需要的函数一致
  TMB = function(hWnd: HWND; lpText, lpCaption: PChar; uType: UINT): Integer; stdcall;

  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  private
    MB: TMB;  {声明函数 MB}
    inst: LongWord;  {声明一个变量来记录要使用的 DLL 句柄}
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
begin
  inst := LoadLibrary('user32.dll');
  if inst <> 0 then
    MB := GetProcAddress(inst, 'MessageBoxW');
//    MB := GetProcAddress(inst, 'MessageBoxA'); {Delphi 2009 之前的版本用这句}
end;

//调用测试：
procedure TForm1.Button1Click(Sender: TObject);
var
  t,b: PChar;
begin
  t := '标题';
  b := '内容';
  MB(0, b, t, 0);
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  FreeLibrary(inst);  {记得释放}
end;

end.