如何继承接口

Question

我从dll 创建了一个 tlb 库。所以我有一些com 对象。 我想扩展接口，但我不能。

_Ckdu_cache：

// *********************************************************************//
// Interface: _Ckdu_cache
// Flags:     (4560) Hidden Dual NonExtensible OleAutomation Dispatchable
// GUID:      {0137B6A2-76D0-3E27-A13C-557542A3AAD5}
// *********************************************************************//
   _Ckdu_cache = interface(IDispatch)
['{0137B6A2-76D0-3E27-A13C-557542A3AAD5}']
function Get_ToString: WideString; safecall;
function Equals(obj: OleVariant): WordBool; safecall;
function GetHashCode: Integer; safecall;
function GetType: _Type; safecall;
function close: Byte; safecall;
function get_capabilities: Integer; safecall;
function read(buf: PSafeArray; num_bytes: Integer): Integer; safecall;
function seek(offset: Int64): Byte; safecall;
function get_pos: Int64; safecall;
function set_tileheader_scope(tnum: Integer; num_tiles: Integer): Byte; safecall;
function set_precinct_scope(unique_id: Int64): Byte; safecall;
procedure Dispose; safecall;
function add_to_databin(databin_class: Integer; codestream_id: Int64; databin_id: Int64; 
                        data: PSafeArray; offset: Integer; num_bytes: Integer; is_final: Byte; 
                        add_as_most_recent: Byte; mark_if_augmented: Byte): PByte1; safecall;

Cockdu_cache ：

// *********************************************************************//
// The Class CoCkdu_cache provides a Create and CreateRemote method to          
// create instances of the default interface _Ckdu_cache exposed by              
// the CoClass Ckdu_cache. The functions are intended to be used by             
// clients wishing to automate the CoClass objects exposed by the         
// server of this typelibrary.                                            
// *********************************************************************//
  CoCkdu_cache = class
    class function Create: _Ckdu_cache;
    class function CreateRemote(const MachineName: string): _Ckdu_cache;
  end;

我的班级：

type
  TKduCache = class(CoCkdu_cache)

我的构造函数：

constructor TKduCache.Create(_targetID, _cachePath: String);
var
  cache : _Ckdu_cache;
begin
  cache:= inherited Create;
end;

错误： 带有消息“不支持接口”的 EIntfCastError

我创建了另一个没有扩展的方法，如下：cache:= Cockdu_cache.Create; 但我得到了同样的错误。我按照这种方法创建了另一个 COM 对象，它们可以工作。但这对我不起作用。如何使用 _Ckdu_cache 方法？

补充：

unit kducache;

interface

uses imagecachestatus, jpipdatasegment, kdu_mni_TLB, globalvalues, SysUtils, Dialogs,
    System.Classes, System.Variants, Winapi.ActiveX, jpipdatabinclass,
  jpipresponse;

type
  TIntArray = array of Integer;
type
  TKduCache = class
  private
    { private declarations }
    //The cache file to use. Null if its not using a chace file.
    cacheFile     : TFileStream;
    Flags         : Word;
    cachePath     : String;
    status        : IImageCacheStatus;
    //The targetID for the image as given by the JPIP server.
    //Should be a unique hash for the image and thus serves
    //as a good way of naming the cache file.
    targetID      : String;
    //The amount of new data placed in this object via the
    //addDataSegment method starting after the initial
    //readCacheFromFile method.
    newData       : Integer;
    //This flags indicates if the server has to be loaded/saved to disk.
    iamPersistent : Boolean;
    class var maxCacheSize  : LongInt;
    cacheExists   : Boolean;

    class function uByteToInt(_x : array of Byte) : TIntArray;
    class function getCacheFiles(_cachePath : String) : TStringStream;
  protected
    { protected declarations }
  public
    FCache: _Ckdu_cache;
    { public declarations }
    procedure setImageCacheStatus(imageCacheStatus : IImageCacheStatus);
    procedure setInitialScope;
    procedure addDataSegment(_data : TJPIPDataSegment);
    class procedure updateCacheDirectory(_cachePath : String; maxSize : Double); overload;
    class procedure updateCacheDirectory(_cachePath : String); overload;
    function getNewDataSize : Integer;
    function getTotalDataSize : Integer;
    function isDataBinCompleted(_binClass : TJPIPDatabinClass; _streamID : Integer; _binID : Integer) : Boolean;
    function Close : Boolean;
    function addJPIPResponseData(jRes : TJPIPResponse) : Boolean;
    function writeCacheToFile : Boolean;
    function readCacheFromFile : Boolean;
    function buildCacheModelUpdateString(force : Boolean) : String;
    function getCacheFile : TStringStream;
    constructor Create(_targetID : String; _cachePath : String); virtual;
//    constructor Create(_targetID : String; _cachePath : String; _iamPersistent : Boolean); overload;
  published
    { published declarations }
  end;
implementation

{ TJHV_Kdu_Cache }

{ TKduCache }

//Main constructor used when you want to use a cache file.
constructor TKduCache.Create(_targetID, _cachePath: String);
begin
  FCache:= CoCkdu_cache.Create;
  targetID:= _targetID;
  cachePath:= _cachePath + '\' + targetID + '.cache';
  cacheExists:= true;
  Flags:= fmOpenReadWrite;
  if _cachePath = '' then
    cacheExists:= false
  else
  begin
    Flags := fmCreate;
    cacheFile:= TFileStream.Create(cachePath, Flags);
  end;
  newData:= 0;

  cacheFile.Free;
  if cacheExists then
    readCacheFromFile;
end;

我在哪里打电话：

TKduCache.Create(jpipTargetID, 'C:\Users\myComputer\Desktop\WorkStation\cache');

Answer 1

您无需使用继承。不要声明派生类。像这样创建接口的实例：

cache := CoCkdu_cache.Create;

然后直接调用cache上的方法。