async void DownloadFile(Uri sourceUri, string destFilename){    cts = new CancellationTokenSource();    StorageFile destinationFile = await KnownFolders.PicturesLibrary.CreateFileAsync(            destFilename, CreationCollisionOption.GenerateUniqueName);    BackgroundDownloader downloader = new BackgroundDownloader();    DownloadOperation download = downloader.CreateDownload(sourceUri, destinationFile);               try    {        Progress<DownloadOperation> progressCallback = new Progress<DownloadOperation>(DownloadProgress);        // Start the download and attach a progress handler.        await download.StartAsync().AsTask(cts.Token, progressCallback);    }    catch (TaskCanceledException) {  /* User cancelled the transfer */ }    catch (Exception ex)          {  /* ...  */ }}

private void CancelAll_Click(object sender, RoutedEventArgs e){    cts.Cancel();    cts.Dispose();    cts = new CancellationTokenSource(); // Re-create the CancellationTokenSource for future downloads.}private void DownloadProgress(DownloadOperation download){    double percent = 100;    if (download.Progress.TotalBytesToReceive > 0)        percent = download.Progress.BytesReceived * 100 / download.Progress.TotalBytesToReceive;     if (download.Progress.HasRestarted)     { /* Download restarted  */ };    if (download.Progress.HasResponseChanged) // We‘ve received new response headers from the server.        Debug.WriteLine(" - Response updated; Header count: " + download.GetResponseInformation().Headers.Count);}

try{    // Create the HttpClient    HttpClient httpClient = new HttpClient();    // Optionally, define HTTP headers    httpClient.DefaultRequestHeaders.Accept.TryParseAdd("application/json");//表示客户端可接收json类型的文本    // Make the call    string responseText = await httpClient.GetStringAsync(        new Uri("http://services.odata.org/Northwind/Northwind.svc/Suppliers"));}catch (Exception ex){   ...}

try{    var client = new HttpClient();    var uri = new Uri(" http://example.com/customers/1");    var response = await client.GetAsync(uri);//GetAsync代替GetstringAsync，可以获得更多内容    // code and results    var statusCode = response.StatusCode;    // EnsureSuccessStatusCode throws exception if not HTTP 200    response.EnsureSuccessStatusCode();    var responseText = await response.Content.ReadAsStringAsync();}catch (Exception ex){    ...}

var client = new HttpClient();// set some headersvar headers = client.DefaultRequestHeaders;//获取头部headers.Referer = new Uri("http://contoso.com");//表示的是上一连接的url，如跳转到本页面的上一页面urlvar ok = headers.UserAgent.TryParseAdd("testprogram/1.0");//表示客户端软件类型// make the requestvar response = await client.GetAsync(uri);// get response content lengthvar length = response.Content.Headers.ContentLength.Value;byte[] buffer = new byte[length];

var client = new HttpClient();    // we‘re sending a delete request    var request = new HttpRequestMessage(HttpMethod.Delete, uri);//http方法Delette    // we don‘t expect a response, but we‘ll snag it anyway    var response = await client.SendRequestAsync(request);

var uri = new Uri("http://example.com/customers/1");try{    var baseFilter = new HttpBaseProtocolFilter();    var cookieManager = baseFilter.CookieManager;    var cookie = new HttpCookie("favoriteColor", ".example.com", "/")         { Value = "purple"};    cookieManager.SetCookie(cookie);    var client = new HttpClient(baseFilter);    await client.PostAsync(uri, new HttpStringContent("Pete"));}catch (Exception ex) { ... }

var baseFilter = new HttpBaseProtocolFilter();var cookieManager = baseFilter.CookieManager;var client = new HttpClient(baseFilter);var cookies = cookieManager.GetCookies(uri);// display cookiesforeach (var cookie in cookies){    CookieList.Text += cookie.Name + " = " + cookie.Value + "\n";}

HttpBaseProtocolFilter filter = new HttpBaseProtocolFilter();// When AutomaticDecompression is true (the default), the Accept-Encoding header is added // to the headers and set to allow gzip and compressfilter.AutomaticDecompression = true;PasswordCredential creds = new PasswordCredential("JumpStart", userName, password);filter.ServerCredential = creds;filter.ProxyCredential = creds;// Create the HttpClientHttpClient httpClient = new HttpClient(filter);

<Grid>        <Grid.RowDefinitions>            <RowDefinition Height="*"/>            <RowDefinition Height="2*"/>            <RowDefinition Height="*"/>        </Grid.RowDefinitions>        <Border x:Name="ImageBorder" Grid.Row="1">            <Image x:Name="MainImage"/>        </Border>        <Button x:Name="DownloadButton" Content="Get Image" HorizontalAlignment="Left" Margin="142,47,0,0" Grid.Row="2" VerticalAlignment="Top" Click="DownloadButton_Click"/>    </Grid>

 private async void DownloadButton_Click(object sender, RoutedEventArgs e)        {            Size downloadSize = new Size(                (int)(ImageBorder.ActualWidth * DisplayInformation.GetForCurrentView().RawPixelsPerViewPixel),                (int)(ImageBorder.ActualHeight * DisplayInformation.GetForCurrentView().RawPixelsPerViewPixel));            //Size downloadSize = new Size(744, 360);            await DownloadAndScale("bg-homepage.jpg", "http://www.qnwfan.com/images/bg-homepage.jpg", downloadSize);            StorageFolder resultsFolder = await ApplicationData.Current.LocalFolder.GetFolderAsync("Results");//进入图片存放的文件夹            StorageFile file = await resultsFolder.GetFileAsync("bg-homepage.jpg");//选取对应图片文件            using (IRandomAccessStream fileStream = await file.OpenAsync(Windows.Storage.FileAccessMode.Read)) //取图片放到MainImage            {                 // Set the image source to the selected bitmap                  BitmapImage bitmapImage = new BitmapImage();                  await bitmapImage.SetSourceAsync(fileStream);                  MainImage.Source = bitmapImage;             }         }        private async Task DownloadAndScale(string outfileName, string downloadUriString, Size scaleSize)        {            Uri downLoadingUri = new Uri(downloadUriString);            HttpClient client = new HttpClient();//创建一个http客户端            using (var response = await client.GetAsync(downLoadingUri))//获取响应            {                var buffer = await response.Content.ReadAsBufferAsync();//缓存响应数据内容                var memoryStream = new InMemoryRandomAccessStream();//创建一个数据流                await memoryStream.WriteAsync(buffer);//把buffer缓存区里的数据写入数据流中                await memoryStream.FlushAsync();//数据流刷新                var decoder = await Windows.Graphics.Imaging.BitmapDecoder.CreateAsync(memoryStream);//数据流解码成图片                var bt = new Windows.Graphics.Imaging.BitmapTransform();//设置图片大小                bt.ScaledWidth = (uint)scaleSize.Width;                bt.ScaledHeight = (uint)scaleSize.Height;                var pixelProvider = await decoder.GetPixelDataAsync(                    decoder.BitmapPixelFormat, decoder.BitmapAlphaMode, bt,                     ExifOrientationMode.IgnoreExifOrientation, ColorManagementMode.ColorManageToSRgb);//使已初步解码后的图片进一步通过一些设置（设置图片帧格式，图片方向，图片大小等）还原成适合在屏幕显示的图片，成为像素提供源                // 既然我们有了像素数据，那么可以把数据储存在文件夹中                var localFolder = Windows.Storage.ApplicationData.Current.LocalFolder;                var resultsFolder = await localFolder.CreateFolderAsync("Results", CreationCollisionOption.OpenIfExists);                var scaledFile = await resultsFolder.CreateFileAsync(outfileName, CreationCollisionOption.ReplaceExisting);                using (var scaledFileStream = await scaledFile.OpenAsync(Windows.Storage.FileAccessMode.ReadWrite))                {                    var encoder = await Windows.Graphics.Imaging.BitmapEncoder.CreateAsync(                        Windows.Graphics.Imaging.BitmapEncoder.JpegEncoderId, scaledFileStream);//                    var pixels = pixelProvider.DetachPixelData();//获取像素数据                    encoder.SetPixelData(                        decoder.BitmapPixelFormat,                        decoder.BitmapAlphaMode,                        (uint)scaleSize.Width,                        (uint)scaleSize.Height,                        decoder.DpiX,                        decoder.DpiY,                        pixels                        );//设置有关帧的像素数据                    await encoder.FlushAsync();//刷新                }