//怎样判断Wifi是否连接 if (Connectivity.NetworkAccess == NetworkAccess.None){    ...}

连接改变的事件，判断事件改变后是否还处于连接状态

Connectivity.ConnectivityChanged += Connectivity_ConnectivityChanged;...void Connectivity_ConnectivityChanged(object sender, ConnectivityChangedEventArgs  e){    bool stillConnected = e.IsConnected;}

在触发一个事件前，先判断网络是否连接的原因是：提升用户体验。

HttpClient是通过Url发送请求和接收服务器响应的组件。

HttpClient client = new HttpClient();

使用HttpClient时使用PostAsnyc方法（异步请求）

HttpClient client = new HttpClient();StringContent content = new StringContent(JsonConvert.SerializeObject(data),Encoding.UTF8, "application/json");HttpResponseMessage response = await client.PostAsync("https://...", content);

HttpClient client = new HttpClient();string text = await client.GetStringAsync("https://...");

 

HttpClient client = new HttpClient();client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

 

HttpClient client = new HttpClient();StringContent content = new StringContent(JsonConvert.SerializeObject(data),Encoding.UTF8, "application/json");HttpResponseMessage response = await client.PutAsync("https://...", content);