轮询作业的状态

默认情况下，应用程序必须轮询作业状态的更改。 若要捕获作业状态的更改，请调用 IBackgroundCopyJob::GetState 方法。 若要捕获传输的字节数和文件数的更改，请调用 IBackgroundCopyJob::GetProgress 方法。 若要检索有关上传-答复作业的答复部分的进度信息，请调用 IBackgroundCopyJob2::GetReplyProgress 方法。 有关使用进度信息的示例，请参阅确定作业的进度。

BG_JOB_STATE 枚举定义作业的状态，BG_JOB_PROGRESS 结构包含有关传输的字节数和文件的信息。

若要使用轮询，需要创建一个机制来启动轮询。 例如，创建计时器或使用用户界面上的“更新”按钮。 但是，在状态或进度发生更改时，注册事件通知和接收事件可能更容易。 有关事件通知的信息，请参阅注册 COM 回调。

以下示例使用计时器轮询作业的状态。 该示例假定 IBackgroundCopyJob 接口指针有效。

HRESULT hr;
IBackgroundCopyJob* pJob;
BG_JOB_STATE State;
HANDLE hTimer = NULL;
LARGE_INTEGER liDueTime;
//IBackgroundCopyError* pError = NULL;
//BG_JOB_PROGRESS Progress;
//WCHAR *JobStates[] = { L"Queued", L"Connecting", L"Transferring",
//                       L"Suspended", L"Error", L"Transient Error",
//                       L"Transferred", L"Acknowledged", L"Canceled"
//                     };

liDueTime.QuadPart = -10000000;  //Poll every 1 second
hTimer = CreateWaitableTimer(NULL, FALSE, L"MyTimer");
SetWaitableTimer(hTimer, &liDueTime, 1000, NULL, NULL, 0);

do
{
  WaitForSingleObject(hTimer, INFINITE);

  //Use JobStates[State] to set the window text in a user interface.
  hr = pJob->GetState(&State);
  if (FAILED(hr))
  {
    //Handle error
  }

  if (BG_JOB_STATE_TRANSFERRED == State)
    //Call pJob->Complete(); to acknowledge that the transfer is complete
    //and make the file available to the client.
  else if (BG_JOB_STATE_ERROR == State || BG_JOB_STATE_TRANSIENT_ERROR == State)
    //Call pJob->GetError(&pError); to retrieve an IBackgroundCopyError interface 
    //pointer which you use to determine the cause of the error.
  else if (BG_JOB_STATE_TRANSFERRING == State)
    //Call pJob->GetProgress(&Progress); to determine the number of bytes 
    //and files transferred.
} while (BG_JOB_STATE_TRANSFERRED != State && 
         BG_JOB_STATE_ERROR != State &&
         BG_JOB_STATE_TRANSIENT_ERROR != State);
CancelWaitableTimer(hTimer);
CloseHandle(hTimer);