从URL到流的图像

我从url获取图片:

BitmapImage image = new BitmapImage(new Uri(article.ImageURL)); NLBI.Thumbnail.Source = image; 

这很完美,现在我需要把它放在一个流中,使其成为字节数组。 我这样做:

 WriteableBitmap wb = new WriteableBitmap(image); MemoryStream ms = new MemoryStream(); wb.SaveJpeg(ms, image.PixelWidth, image.PixelHeight, 0, 100); byte[] imageBytes = ms.ToArray(); 

并且代码因NullReference而失败,如何解决?

您会收到NullReferenceexception,因为在使用它时图像仍未加载。 您可以等待ImageOpened事件,然后使用它:

 var image = new BitmapImage(new Uri(article.ImageURL)); image.ImageOpened += (s, e) => { image.CreateOptions = BitmapCreateOptions.None; WriteableBitmap wb = new WriteableBitmap(image); MemoryStream ms = new MemoryStream(); wb.SaveJpeg(ms, image.PixelWidth, image.PixelHeight, 0, 100); byte[] imageBytes = ms.ToArray(); }; NLBI.Thumbnail.Source = image; 

其他选项是使用WebClient直接获取图像文件的流:

 WebClient client = new WebClient(); client.OpenReadCompleted += (s, e) => { byte[] imageBytes = new byte[e.Result.Length]; e.Result.Read(imageBytes, 0, imageBytes.Length); // Now you can use the returned stream to set the image source too var image = new BitmapImage(); image.SetSource(e.Result); NLBI.Thumbnail.Source = image; }; client.OpenReadAsync(new Uri(article.ImageURL)); 
 var webClient = new WebClient(); byte[] imageBytes = webClient.DownloadData(article.ImageURL); 

你可以用这个:

  private async Task GetImageAsByteArray(string urlImage, string urlBase) { var client = new HttpClient(); client.BaseAddress = new Uri(urlBase); var response = await client.GetAsync(urlImage); return await response.Content.ReadAsByteArrayAsync(); }