将其保存在工具箱中:)

Save this in your toolbox :)

    public static Task<Stream> DownloadFile(Uri url)
    {
        var tcs = new TaskCompletionSource<Stream>();
        var wc = new WebClient();
        wc.OpenReadCompleted += (s, e) =>
        {
            if (e.Error != null) tcs.TrySetException(e.Error);
            else if (e.Cancelled) tcs.TrySetCanceled();
            else tcs.TrySetResult(e.Result);
        };
        wc.OpenReadAsync(url);
        return tcs.Task;
    }