Question

我正在使用此方法从服务器同步下载图像数组

Bitmap GetImageBitmapFromUrl(string url)
{
    Bitmap imageBitmap = null;
    try
    {
        using (var webClient = new WebClient())
        {
            var imageBytes = webClient.DownloadData(url);
            if (imageBytes != null && imageBytes.Length > 0)
            {
                imageBitmap = BitmapFactory.DecodeByteArray(imageBytes, 0, imageBytes.Length);
            }
        }
    }
    catch
    {
        //Silence is gold.
    }
    displayPic();
    return imageBitmap;
}

但我现在想要异步使用这个方法。我改变它看起来像这样

async Task<Bitmap> GetImageBitmapFromUrl(string url)
{
    Bitmap imageBitmap = null;
    try
    {
        using (var webClient = new WebClient())
        {
            var imageBytes = await webClient.DownloadStringTaskAsync(url);
            if (imageBytes != null && imageBytes.Length > 0)
            {
                //imageBitmap = BitmapFactory.DecodeByteArray(Encoding.ASCII.GetBytes(imageBytes), 0, imageBytes.Length);
                imageBitmap = BitmapFactory.DecodeByteArray(Encoding.BigEndianUnicode.GetBytes(imageBytes), 0, imageBytes.Length);
            }
        }
    }
    catch
    {
        //Silence is gold.
    }
    displayPic();
    return imageBitmap;
}

但是从字符串到字节数组的转换不起作用，我每次都从方法中收到一个null对象。

导致imageBitmap变量在第二种方法中变为null的原因是什么？我该如何解决？

Answer 1

您将获得字节数组而不是字符串。改变这个：

var imageBytes = await webClient.DownloadStringTaskAsync(url);

到此：

var imageBytes = await webClient.DownloadDataTaskAsync(url);

如何异步下载图像

1 个答案: