主控程序之插件装载器一

对于DELPHI来说，总共支持俩种类型的插件：DLL和BPL方式的插件。

对于比较完美的插件框架来说，俩种类型的插件都要支持。

unit DLLLoader;

interface

uses
  windows, Classes, SysUtils, Forms, StrUtils;

type
  TLibraryType = (dll, bpl);  // plugin type: dll or bpl

  TDLLLoader = class(TObject)
  private
    FHandle: THandle;
    FFileName: string;
    FLibraryType: TLibraryType;
    procedure SetFileName(const Value: string);
  protected
    function GetApplicationPath: string;
  public
    constructor Create(DllFileName: string);
    destructor destroy(); override;
    procedure FreeHandle(); virtual;
    property FileName: string read FFileName write SetFileName;
    property DLLHandle: THandle read FHandle;
  end;

implementation

  { TDLLLoader }

constructor TDLLLoader.Create(DllFileName: string);
var
  ext: string;
begin
  ext := RightStr(DllFileName, 4);
  if ext = '.dll' then FLibraryType := dll
  else if ext = '.bpl' then FLibraryType := bpl;
  FileName := DLLFileName;
end;

destructor TDLLLoader.destroy;
begin
  FreeHandle;
  inherited;
end;

procedure TDLLLoader.FreeHandle;
begin
  if FHandle <> 0 then
    case FLibraryType of
      dll: FreeLibrary(FHandle);
      bpl: UnloadPackage(FHandle);
    end;
end;

function TDLLLoader.GetApplicationPath: string;
begin
  result := ExtractFilePath(Application.ExeName);
end;

procedure TDLLLoader.SetFileName(const Value: string);
begin
  if FFileName <> Value then
  begin
    FFileName := Value;
    case FLibraryType of
      dll: FHandle := LoadLibrary(PChar(FFileName));
      bpl: FHandle := LoadPackage(FFileName)
    end;
    if FHandle = 0 then
      raise Exception.Create(Value + 'load plugin fail.');
  end;
end;

end.