範例：一般類別

發行項
02/14/2024

您可以使用本主題中的程式碼範例作為許多背景智慧型手機傳送服務（BITS）應用程式的起點，這些應用程式執行 COM 初始化、需要錯誤處理，以及接收回呼通知。

下列程式代碼範例會定義例外狀況類別來處理錯誤。

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

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

MyException 類別是接受 HRESULT 程式代碼和錯誤字串的泛型例外狀況類別。

下列程式代碼範例會定義 CoInitializeEx 函式的資源取得協助程序類別。

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

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

CCoInitializer 類別會處理 COM 初始化的資源配置和解除分配。這個類別可讓解構函式在類別超出範圍時呼叫。這個類別不需要在每個例外狀況區塊之後呼叫 CoUninitialize 方法。

下列程式代碼範例是 CNotifyInterface 回呼介面的宣告。

// 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&);
};

衍生自 IBackgroundCopyCallback 介面的 CNotifyInterface 類別。 CNotifyInterface 類別會實作 IUnknown 介面。如需詳細資訊，請參閱 IUnknown。

CNotifyInterface 使用下列方法來接收作業已完成、已修改或處於錯誤狀態的通知：JobTransferred、JobModification 和 JobError。 所有這些方法都會採用 IBackgroundCopyJob 作業物件。

此範例會使用 CoTaskMemFree 釋放記憶體資源。

下列程式代碼範例是IBackgroundCopyCallback 回呼介面的實作。

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;
}

下列頭檔用於一般程式代碼類別。這些類別會用於先前的程式代碼範例中。

// 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&);
};

下列範例程式代碼是通用程式代碼類別的實作。

//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;
}

IUnknown
IBackgroundCopyCallback
IBackgroundCopyJob
CoInitializeEx
CoUninitialize

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範例：一般類別

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範例：一般類別

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