windows-8 – 如何取消HttpClient GET Web请求

protected async override void OnNavigatedTo(NavigationEventArgs e)
{
    await HttpGetRequest();
}

public CancellationTokenSource cts = new CancellationTokenSource();
private async Task HttpGetRequest()
{
    try
    {
        DateTime now = DateTime.Now;
        var httpClient = new HttpClient();
        var message = new HttpRequestMessage(HttpMethod.Get,"https://itunes.apple.com/us/rss/toppaidapplications/limit=400/genre=6000/json");
        var response = await httpClient.SendAsync(message,cts.Token);
        System.Diagnostics.Debug.WriteLine("HTTP Get request completed. Time taken : " + (DateTime.Now - now).TotalSeconds + " seconds.");
    }
    catch (TaskCanceledException)
    {
        System.Diagnostics.Debug.WriteLine("HTTP Get request canceled.");
    }
}

private void btnCancel_Click(object sender,RoutedEventArgs e)
{
    cts.Cancel();
}