为什么VC2008认为这个类是抽象的？
我正在编写一些代码来使用 DirectShow 处理来自某些摄像机的视频输入，因此我必须实现 ISampleGrabberCB。
我实现该接口的类可以正常编译，但是当我尝试实例化它时，编译器会引发“错误 C2259：'SampleGrabberCB'：无法实例化抽象类”。
这是我正在实现的接口：
interface ISampleGrabberCB : public IUnknown {
virtual STDMETHODIMP SampleCB( double SampleTime, IMediaSample *pSample ) = 0;
virtual STDMETHODIMP BufferCB( double SampleTime, BYTE *pBuffer, long BufferLen ) = 0;
};
这是我的 SampleGrabberCB 标头：
#pragma once
#include "stdafx.h"
class SampleGrabberCB : public ISampleGrabberCB {
private:
int _refCount;
DShowCaptureDevice* _parent;
public:
// SampleGrabberCB();
SampleGrabberCB(DShowCaptureDevice* parent);
~SampleGrabberCB();
virtual STDMETHODIMP BufferCB(double sampleTime, BYTE* pBuffer, long bufferLen);
virtual STDMETHODIMP SampleCB(double sampleTime, IMediaSample * pSample, long bufferLen);
#pragma region IUnknown
virtual HRESULT STDMETHODCALLTYPE QueryInterface(REFIID riid, void** ppv) {
if( riid == IID_ISampleGrabberCB || riid == IID_IUnknown ) {
*ppv = (void *) static_cast<ISampleGrabberCB*> ( this );
return NOERROR;
}
return E_NOINTERFACE;
}
virtual ULONG STDMETHODCALLTYPE AddRef() {
return ++_refCount;
}
virtual ULONG STDMETHODCALLTYPE Release() {
int n = --_refCount;
if (n <= 0) {
delete this;
}
return n;
}
#pragma endregion
};
这是实现 SampleGrabberCB.cpp：
#include "StdAfx.h"
#include "SampleGrabberCB.h"
//SampleGrabberCB::SampleGrabberCB() {
// _parent = NULL;
//}
SampleGrabberCB::SampleGrabberCB(DShowCaptureDevice* parent) {
_parent = parent;
}
SampleGrabberCB::~SampleGrabberCB() {
}
STDMETHODIMP SampleGrabberCB::BufferCB(double sampleTime, BYTE *pBuffer, long bufferLen) {
// dummy value for now
return -50;
}
STDMETHODIMP SampleGrabberCB::SampleCB(double sampleTime, IMediaSample *pSample, long bufferLen) {
// dummy value for now
return 100;
}
这是我如何使用它：
SampleGrabberCB* callback = new SampleGrabberCB(device);
有什么想法吗？谢谢！
I'm writing some code to handle video input from some cameras using DirectShow, so I have to implement ISampleGrabberCB.
My class that implements the interface compiles okay, but when I try to instantiate it the compiler raises "error C2259: 'SampleGrabberCB' : cannot instantiate abstract class".
Here is the interface I'm implementing:
interface ISampleGrabberCB : public IUnknown {
virtual STDMETHODIMP SampleCB( double SampleTime, IMediaSample *pSample ) = 0;
virtual STDMETHODIMP BufferCB( double SampleTime, BYTE *pBuffer, long BufferLen ) = 0;
};
Here is my SampleGrabberCB header:
#pragma once
#include "stdafx.h"
class SampleGrabberCB : public ISampleGrabberCB {
private:
int _refCount;
DShowCaptureDevice* _parent;
public:
// SampleGrabberCB();
SampleGrabberCB(DShowCaptureDevice* parent);
~SampleGrabberCB();
virtual STDMETHODIMP BufferCB(double sampleTime, BYTE* pBuffer, long bufferLen);
virtual STDMETHODIMP SampleCB(double sampleTime, IMediaSample * pSample, long bufferLen);
#pragma region IUnknown
virtual HRESULT STDMETHODCALLTYPE QueryInterface(REFIID riid, void** ppv) {
if( riid == IID_ISampleGrabberCB || riid == IID_IUnknown ) {
*ppv = (void *) static_cast<ISampleGrabberCB*> ( this );
return NOERROR;
}
return E_NOINTERFACE;
}
virtual ULONG STDMETHODCALLTYPE AddRef() {
return ++_refCount;
}
virtual ULONG STDMETHODCALLTYPE Release() {
int n = --_refCount;
if (n <= 0) {
delete this;
}
return n;
}
#pragma endregion
};
and this is the implementation SampleGrabberCB.cpp:
#include "StdAfx.h"
#include "SampleGrabberCB.h"
//SampleGrabberCB::SampleGrabberCB() {
// _parent = NULL;
//}
SampleGrabberCB::SampleGrabberCB(DShowCaptureDevice* parent) {
_parent = parent;
}
SampleGrabberCB::~SampleGrabberCB() {
}
STDMETHODIMP SampleGrabberCB::BufferCB(double sampleTime, BYTE *pBuffer, long bufferLen) {
// dummy value for now
return -50;
}
STDMETHODIMP SampleGrabberCB::SampleCB(double sampleTime, IMediaSample *pSample, long bufferLen) {
// dummy value for now
return 100;
}
Here is how I'm using it:
SampleGrabberCB* callback = new SampleGrabberCB(device);
Any ideas? Thanks!
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评论（4）
接口中声明的
SampleCB没有SampleGrabberCB类中存在的第三个参数 (bufferLen)。SampleCBas declared in the interface doesn't have the third parameter (bufferLen) that is present in theSampleGrabberCBclass.您的 SampleCB 方法与基（抽象）类中的方法不匹配。
相对
Your SampleCB method doesn't match the method in the base (abstract) class.
versus
您的虚拟 STDMETHODIMP SampleCB(double sampleTime, IMediaSample * pSample, long bufferLen) 方法的签名与接口中纯虚拟方法的签名不匹配 - 您需要删除 bufferlen 参数。
The signature of your virtual STDMETHODIMP SampleCB(double sampleTime, IMediaSample * pSample, long bufferLen) method doesn't matcht that of the pure virtual mether in the Interface - you need to drop the bufferlen argument.
SampleCB 方法中的方法签名似乎不同。 On case 有 2 个参数，其他 3 个参数。
It looks like the method signature is different in SampleCB method. On case has 2 parameters and the other 3 parameters.