从方法外部取消 GetAsync 请求

我有大量的异步请求。在某些时候，当应用程序停用（暂停）时，我需要取消所有请求。我正在寻找一种解决方案来取消异步方法之外的请求。有人能指出我正确的方向吗？

这是代码块。

异步方法：

public async void GetDetailsAsync(string url)
{
    if (this.LastDate == null)
    {
        this.IsDetailsLoaded = "visible";
        NotifyPropertyChanged("IsDetailsLoaded");
        Uri uri = new Uri(url);
        HttpClient client = new HttpClient();
        HtmlDocument htmlDocument = new HtmlDocument();
        HtmlNode htmlNode = new HtmlNode(0, htmlDocument, 1);
        MovieData Item = new MovieData();
        string HtmlResult;

        try
        {
            HtmlRequest = await client.GetAsync(uri);
            HtmlResult = await HtmlRequest.Content.ReadAsStringAsync();
        }
        ...

调用方法：

for (int i = 0; i < App.ViewModel.Today.Items.Count; i++)
{
    App.ViewModel.Today.Items[i].GetDetailsAsync(App.ViewModel.Today.Items[i].DetailsUrl);
}

停用事件：

private void Application_Deactivated(object sender, DeactivatedEventArgs e)
{
    //Here i need to stop all requests.
}

你刚才创建单个（共享）实例CancellationTokenSource http://msdn.microsoft.com/en-us/library/dd997364%28v=vs.110%29.aspx:

private CancellationTokenSource _cts = new CancellationTokenSource();

Then, 将所有异步操作绑定到该令牌中 http://blogs.msdn.com/b/lucian/archive/2012/12/08/await-httpclient-getstringasync-and-cancellation.aspx:

public async void GetDetailsAsync(string url)
{
  ...
  HtmlRequest = await client.GetAsync(uri, _cts.Token);
  ...
}

最后，在适当的时候取消CTS：

private void Application_Deactivated(object sender, DeactivatedEventArgs e)
{
  _cts.Cancel();
  _cts = new CancellationTokenSource();
}