//首先判断下载存储区是否存在,不存在则创建一个using (IsolatedStorageFile isoStore = IsolatedStorageFile.GetUserStoreForApplication()){if (!isoStore.DirectoryExists("/shared/transfers"))        {                isoStore.CreateDirectory("/shared/transfers");        }}//指定需要下载的文件的URLstring downloadurl="http://create.msdn.com/assets/cms/images/samples/windowsphonetestfile1.png";Uri transferUri = new Uri(Uri.EscapeUriString(downloadurl), UriKind.RelativeOrAbsolute);//创建Request对象BackgroundTransferRequest transferRequest = new BackgroundTransferRequest(transferUri);//设置一些请求的属性transferRequest.Method = "GET";string downloadFile = "windowsphonetestfile1.png";Uri downloadUri = new Uri("shared/transfers/" + downloadFile, UriKind.RelativeOrAbsolute);transferRequest.DownloadLocation = downloadUri;transferRequest.Tag = downloadFile;transferRequest.TransferPreferences = TransferPreferences.AllowCellularAndBattery;//这里需要根据情况进行设置,详细内容参见这里http://msdn.microsoft.com/zh-cn/library/microsoft.phone.backgroundtransfer.transferpreferences(v=vs.92).aspx//添加到下载列表中.这里要注意的是,每一个应用同时只能有5个请求在下载列表中BackgroundTransferService.Add(transferRequest);

//首先声明一个List来存放下载的列表IEnumerable<BackgroundTransferRequest> transferRequests;//然后写一个方法来刷新UI,这个刷新方式挺奇特.- -!private void UpdateRequestsList(){//如果list不为空,那么首先将他释放掉.不然会内存溢出        if (transferRequests != null)        {foreach (var request in transferRequests)                {                    request.Dispose();                }        }//然后把BackgroundTransferService里面的Request放到这个List里        transferRequests = BackgroundTransferService.Requests;}

//接下来,为每一个请求绑定两个事件foreach (var transfer in transferRequests){        transfer.TransferStatusChanged += new EventHandler<BackgroundTransferEventArgs>(transfer_TransferStatusChanged);        transfer.TransferProgressChanged += new EventHandler<BackgroundTransferEventArgs>(transfer_TransferProgressChanged);}

//在每次事件触发的时候,去做相应操作        void transfer_TransferStatusChanged(object sender, BackgroundTransferEventArgs e)        {            ProcessTransfer(e.Request);            UpdateUI();        }

void transfer_TransferProgressChanged(object sender, BackgroundTransferEventArgs e)        {            UpdateUI();        }

//这个方法就是用来统一处理每一个请求需要做的操作        private void ProcessTransfer(BackgroundTransferRequest transfer)        {switch (transfer.TransferStatus)            {case TransferStatus.Completed:

//一般来说,服务器返回200或者206就表示传输成功完成,我们可以文件移到另外一个地方                    if (transfer.StatusCode == 200 || transfer.StatusCode == 206)                    {                        RemoveTransferRequest(transfer.RequestId);

using (IsolatedStorageFile isoStore = IsolatedStorageFile.GetUserStoreForApplication())                        {string filename = transfer.Tag;if (isoStore.FileExists(filename))                            {                                isoStore.DeleteFile(filename);                            }                            isoStore.MoveFile(transfer.DownloadLocation.OriginalString, filename);                        }                    }else                    {                        RemoveTransferRequest(transfer.RequestId);

if (transfer.TransferError != null)                        {// Handle TransferError if one exists.                        }                    }break;            }        }