检查与HttpClient的Internet连接

我很难理解波纹管代码如何处理偶尔的互联网连接丢失。 理想情况下，我想暂停应用程序，一旦连接丢失，并在它再次启动时恢复。 有关于如何做的指导方针吗？

HttpClientHandler clientHandler = new HttpClientHandler(); clientHandler.UseDefaultCredentials = true; HttpClient client = new HttpClient(clientHandler) { MaxResponseContentBufferSize = 1000000 }; HttpResponseMessage response = await client.GetAsync(Url, ct); 

Answer 1

以下示例不是直接解决方案，但它是我构建的示例，用于说明如何在脱机时将“预先封装”内容返回给请求，然后在恢复连接时返回在线状态。 如果你能得到我在这里所做的事情，建立你想要的东西应该相当容易。

  [Fact] public async Task Getting_a_response_when_offline() { var offlineHandler = new OfflineHandler(new HttpClientHandler(), new Uri("http://oak:1001/status")); offlineHandler.AddOfflineResponse(new Uri("http://oak:1001/ServerNotRunning"), new HttpResponseMessage(HttpStatusCode.NonAuthoritativeInformation) { Content = new StringContent("Here's an old copy of the information while we are offline.") }); var httpClient = new HttpClient(offlineHandler); var retry = true; while (retry) { var response = await httpClient.GetAsync(new Uri("http://oak:1001/ServerNotRunning")); if (response.StatusCode == HttpStatusCode.OK) retry = false; Thread.Sleep(10000); } } public class OfflineHandler : DelegatingHandler { private readonly Uri _statusMonitorUri; private readonly Dictionary _offlineResponses = new Dictionary(); private bool _isOffline = false; private Timer _timer; public OfflineHandler(HttpMessageHandler innerHandler, Uri statusMonitorUri) { _statusMonitorUri = statusMonitorUri; InnerHandler = innerHandler; } public void AddOfflineResponse(Uri uri, HttpResponseMessage response) { _offlineResponses.Add(uri,response); } protected async override Task SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) { if (_isOffline == true) return OfflineResponse(request); try { var response = await base.SendAsync(request, cancellationToken); if (response.StatusCode == HttpStatusCode.ServiceUnavailable || response.StatusCode == HttpStatusCode.BadGateway) { MonitorOfflineState(); return OfflineResponse(request); } return response; } catch (WebException ex) { MonitorOfflineState(); return OfflineResponse(request); } } private void MonitorOfflineState() { _isOffline = true; _timer = new Timer( async state => { var request = new HttpRequestMessage() {RequestUri = _statusMonitorUri}; try { var response = await base.SendAsync(request, new CancellationToken()); if (response.StatusCode == HttpStatusCode.OK) { _isOffline = false; _timer.Dispose(); } } catch { } }, null, new TimeSpan(0,0,0),new TimeSpan(0,1,0)); } private HttpResponseMessage OfflineResponse(HttpRequestMessage request) { if (_offlineResponses.ContainsKey(request.RequestUri)) { return _offlineResponses[request.RequestUri]; } return new HttpResponseMessage(HttpStatusCode.ServiceUnavailable); } } }