Example: Common Classes

You can use the code examples in this topic as a starting point for many Background Intelligent Transfer Service (BITS) applications that perform COM initialization, need error handling, and receive callback notifications.

The following code example defines an exception class to handle errors.

class MyException
{
public:
    MyException(HRESULT hr, LPWSTR message):Error(hr), Message(message)
    {

    }
    HRESULT Error;
    std::wstring Message;
};

The MyException class is a generic exception class that accepts an HRESULT code and error string.

The following code example defines a resource acquisition helper class for the CoInitializeEx function.

class CCoInitializer 
{
public:
    CCoInitializer( DWORD dwCoInit ) 
    { 
        HRESULT hr = CoInitializeEx( NULL, dwCoInit );
        if (FAILED(hr))
        {
            throw MyException(hr,L"CoInitialize");
        }
    } 

    ~CCoInitializer() throw() 
    { 
        CoUninitialize(); 
    } 
};

The CCoInitializer class deals with resource allocation and deallocation for COM initialization. This class enables the destructor to be called when the class goes out of scope. This class eliminates the need for the CoUninitialize method to be called after every exception block.

The following code example is the declaration of the CNotifyInterface callback interface.

// Implementation of the Callback interface
//
class CNotifyInterface : public IBackgroundCopyCallback
{
    LONG m_lRefCount;

public:
    //Constructor
    CNotifyInterface() {m_lRefCount = 1;};

//Destructor
    ~CNotifyInterface() {};

    //IUnknown methods
    HRESULT __stdcall QueryInterface(REFIID riid, LPVOID *ppvObj);
    ULONG __stdcall AddRef();
    ULONG __stdcall Release();

    //IBackgroundCopyCallback methods
    HRESULT __stdcall JobTransferred(IBackgroundCopyJob* pJob);
    HRESULT __stdcall JobError(IBackgroundCopyJob* pJob, IBackgroundCopyError* pError);
    HRESULT __stdcall JobModification(IBackgroundCopyJob* pJob, DWORD dwReserved);

private:
    CNotifyInterface(const CNotifyInterface&);
    CNotifyInterface& operator=(const CNotifyInterface&);
};

The CNotifyInterface class derived from the IBackgroundCopyCallback interface. The CNotifyInterface class implements the IUnknown interface. For more information, see IUnknown.

CNotifyInterface uses the following methods to receive notification that a job is complete, has been modified, or is in an error state: JobTransferred, JobModification, and JobError. All of these methods take an IBackgroundCopyJob job object.

This example uses the CoTaskMemFree to free memory resources.

The following code example is the implementation of the IBackgroundCopyCallback callback interface.

HRESULT CNotifyInterface::QueryInterface(REFIID riid, LPVOID* ppvObj) 
{
    if (riid == __uuidof(IUnknown) || riid == __uuidof(IBackgroundCopyCallback)) 
    {
        *ppvObj = this;
    }
    else
    {
        *ppvObj = NULL; 
        return E_NOINTERFACE;
    }

    AddRef();
    return NOERROR;
}

ULONG CNotifyInterface::AddRef() 
{
    return InterlockedIncrement(&m_lRefCount);
}

ULONG CNotifyInterface::Release() 
{
    // not thread safe
    ULONG  ulCount = InterlockedDecrement(&m_lRefCount);

    if(0 == ulCount) 
    {
        delete this;
    }

    return ulCount;
}

HRESULT CNotifyInterface::JobTransferred(IBackgroundCopyJob* pJob)
{
    HRESULT hr;

    wprintf(L"Job transferred. Completing Job...\n");
    hr = pJob->Complete();
    if (FAILED(hr))
    {
        //BITS probably was unable to rename one or more of the 
        //temporary files. See the Remarks section of the IBackgroundCopyJob::Complete 
        //method for more details.
        wprintf(L"Job Completion Failed with error %x\n", hr);
    }

    PostQuitMessage(0);

    //If you do not return S_OK, BITS continues to call this callback.
    return S_OK;
}

HRESULT CNotifyInterface::JobModification(IBackgroundCopyJob* pJob, DWORD dwReserved)
{
    return S_OK;
}

HRESULT CNotifyInterface::JobError(IBackgroundCopyJob* pJob, IBackgroundCopyError* pError)
{
    WCHAR* pszJobName = NULL;
    WCHAR* pszErrorDescription = NULL;

    //Use pJob and pError to retrieve information of interest. For example,
    //if the job is an upload reply, call the IBackgroundCopyError::GetError method 
    //to determine the context in which the job failed. 

    wprintf(L"Job entered error state...\n");
    HRESULT hr = pJob->GetDisplayName(&pszJobName);
    if (FAILED(hr))
    {
        wprintf(L"Unable to get job name\n");
    }

    hr = pError->GetErrorDescription(GetUserDefaultUILanguage(), &pszErrorDescription);
    if (FAILED(hr))
    {
        wprintf(L"Unable to get error description\n");
    }
    if (pszJobName && pszErrorDescription)
    {
        wprintf(L"Job %s ",pszJobName);
        wprintf(L"encountered the following error:\n");
        wprintf(L"%s\n",pszErrorDescription);
    }
    
    // Clean up
    CoTaskMemFree(pszJobName);
    CoTaskMemFree(pszErrorDescription);

    PostQuitMessage(hr);

    //If you do not return S_OK, BITS continues to call this callback.
    return S_OK;
}

The following header file is used for the common code classes. These classes are used in the previous code examples.

// commoncode.h
#pragma once

//
// Exception class used for error handling
//
class MyException
{
public:
    MyException(HRESULT hr, LPWSTR message):Error(hr), Message(message)
    {

    }
    HRESULT Error;
    std::wstring Message;
};

// CoInitialize helper class
class CCoInitializer 
{
public:
    CCoInitializer( DWORD dwCoInit ) 
    { 
        HRESULT hr = CoInitializeEx( NULL, dwCoInit );
        if (FAILED(hr))
        {
            throw MyException(hr,L"CoInitialize");
        }
    } 

    ~CCoInitializer() throw() 
    { 
        CoUninitialize(); 
    } 
};

//
// Implementation of the Callback interface
//
class CNotifyInterface : public IBackgroundCopyCallback
{
    LONG m_lRefCount;

public:
    //Constructor, Destructor
    CNotifyInterface() {m_lRefCount = 1;};
    ~CNotifyInterface() {};

    //IUnknown
    HRESULT __stdcall QueryInterface(REFIID riid, LPVOID *ppvObj);
    ULONG __stdcall AddRef();
    ULONG __stdcall Release();

    //IBackgroundCopyCallback2 methods
    HRESULT __stdcall JobTransferred(IBackgroundCopyJob* pJob);
    HRESULT __stdcall JobError(IBackgroundCopyJob* pJob, IBackgroundCopyError* pError);
    HRESULT __stdcall JobModification(IBackgroundCopyJob* pJob, DWORD dwReserved);
private:
    CNotifyInterface(const CNotifyInterface&);
    CNotifyInterface& operator=(const CNotifyInterface&);
};

The following example code is the implementation of the common code classes.

//commoncode.cpp

#include <bits.h>
#include <bits4_0.h>
#include <stdio.h>
#include <tchar.h>
#include <lm.h>
#include <iostream>
#include <exception>
#include <string>
#include <atlbase.h>
#include <memory>
#include <new>
#include "CommonCode.h"

HRESULT CNotifyInterface::QueryInterface(REFIID riid, LPVOID* ppvObj) 
{
    if (riid == __uuidof(IUnknown) || riid == __uuidof(IBackgroundCopyCallback)) 
    {
        *ppvObj = this;
    }
    else
    {
        *ppvObj = NULL; 
        return E_NOINTERFACE;
    }

    AddRef();
    return NOERROR;
}

ULONG CNotifyInterface::AddRef() 
{
    return InterlockedIncrement(&m_lRefCount);
}

ULONG CNotifyInterface::Release() 
{
    // not thread safe
    ULONG  ulCount = InterlockedDecrement(&m_lRefCount);

    if(0 == ulCount) 
    {
        delete this;
    }

    return ulCount;
}

HRESULT CNotifyInterface::JobTransferred(IBackgroundCopyJob* pJob)
{
    HRESULT hr;

    wprintf(L"Job transferred. Completing Job...\n");
    hr = pJob->Complete();
    if (FAILED(hr))
    {
        //BITS probably was unable to rename one or more of the 
        //temporary files. See the Remarks section of the IBackgroundCopyJob::Complete 
        //method for more details.
        wprintf(L"Job Completion Failed with error %x\n", hr);
    }

    PostQuitMessage(0);

    //If you do not return S_OK, BITS continues to call this callback.
    return S_OK;
}

HRESULT CNotifyInterface::JobModification(IBackgroundCopyJob* pJob, DWORD dwReserved)
{
    return S_OK;
}

HRESULT CNotifyInterface::JobError(IBackgroundCopyJob* pJob, IBackgroundCopyError* pError)
{
    WCHAR* pszJobName = NULL;
    WCHAR* pszErrorDescription = NULL;

    //Use pJob and pError to retrieve information of interest. For example,
    //if the job is an upload reply, call the IBackgroundCopyError::GetError method 
    //to determine the context in which the job failed.

    wprintf(L"Job entered error state...\n");
    HRESULT hr = pJob->GetDisplayName(&pszJobName);
    if (FAILED(hr))
    {
        wprintf(L"Unable to get job name\n");
    }

    hr = pError->GetErrorDescription(GetUserDefaultUILanguage(), &pszErrorDescription);
    if (FAILED(hr))
    {
        wprintf(L"Unable to get error description\n");
    }
    if (pszJobName && pszErrorDescription)
    {
        wprintf(L"Job %s ",pszJobName);
        wprintf(L"encountered the following error:\n");
        wprintf(L"%s\n",pszErrorDescription);
    }

    CoTaskMemFree(pszJobName);
    CoTaskMemFree(pszErrorDescription);

    PostQuitMessage(hr);

    //If you do not return S_OK, BITS continues to call this callback.
    return S_OK;
}

Related topics

IUnknown

IBackgroundCopyCallback

IBackgroundCopyJob

CoInitializeEx

CoUninitialize