Question

通过此链接提出问题并尝试实施已接受的答案：

Invoking a method asynchronously and/or on its own thread to increase performance

我正在尝试使用名为DownloadImageFromUrl的简单方法，该方法接受字符串Url并将Bitmap返回到将使用async运行的方法。目前的方法：

private Bitmap DownloadImageFromUrl(string url)
    {
        //// METHOD A:
        //WebRequest request = System.Net.WebRequest.Create(url);
        //WebResponse response = request.GetResponse();
        //Stream responseStream = response.GetResponseStream();
        //return new Bitmap(responseStream);

        // METHOD B:
        using (WebClient client = new WebClient())
        {
            byte[] data = client.DownloadData(url);
            using (MemoryStream mem = (data == null) ? null : new MemoryStream(data))
            {
                return (data == null || mem == null) ? null : (Bitmap)Image.FromStream(mem);
            }
        }
    }

制作这个异步的想法是这样的，在另一种方法中，我可以用这个做这样的事情：

public async Task<HttpResponseMessage> process(string image)
{
 var task = DownloadFromBlobAsync(image);
 var setupData = DoSomeSetup();
 var image = await task;
 return DrawTextOnImage(image, setupData);
}

DoSomeSetup需要相当长的时间并且下载图像也是如此，所以我想在设置发生时在自己的线程上下载图像。

我不确定有哪些工具可用于更改此downloadImageFromUrl以返回任务..任何资源或代码示例都会有所帮助。

Answer 1

来自charlie的How to download image from url using c#示例：

    using (WebClient client = new WebClient()) 
  {
    client.DownloadFileAsync(new Uri(url), @"c:\temp\image35.png");
    client.DownloadFile(new Uri(url), @"c:\temp\image35.png");
   }

EDITED

using (IsolatedStorageFile myIsolatedStorage = IsolatedStorageFile.GetUserStoreForApplication())
{
    IsolatedStorageFileStream fileStream = myIsolatedStorage.CreateFile("fileNameHere");

    BitmapImage bitmap = new BitmapImage();
    var stream = await DownloadFile(new Uri("http://someuri.com", UriKind.Absolute));
    bitmap.SetSource(stream);
    WriteableBitmap wb = new WriteableBitmap(bitmap);

    // Encode WriteableBitmap object to a JPEG stream.
    Extensions.SaveJpeg(wb, fileStream, wb.PixelWidth, wb.PixelHeight, 0, 85);
    fileStream.Close();
}

可能重复：

How to download image from url using c#

使用Async下载图像并保存到位图

1 个答案: