无网络时代码退出，无法捕获异常

Question

你好

此代码在在有网络时完美运行，当离线未连接到互联网时，我想分配静态引脚，但此代码正在退出并且没有使用 list1 加载问题。

异常：

Exception thrown: 'System.Net.Sockets.SocketException' in System.Private.CoreLib.dll

Exception thrown: 'System.Net.Http.HttpRequestException' in System.Private.CoreLib.dll

The program '[6584] MauiAppMCQs.exe' has exited with code 0 (0x0).

@inject NavigationManager Navigation

@using System.Text;

@using System.Net.Http.Headers;

@using Microsoft.AspNetCore.Components;

@using Newtonsoft.Json;

@using Microsoft.JSInterop;

@page "/Login"

<h3>Login</h3>

<EditForm Model="@submitActivity" OnSubmit="@Submit">

<br />

<div class="row">

<div class="col-md-3">

<p>PIN</p>

</div>

<div class="col-md-4">

<input placeholder="PIN" @bind="@pin" />

</div>

</div>

<div>

<button type="submit">Submit</button>

</div>

<div>

        @errmsg

</div>

</EditForm>

@code {

    private int pin; private string jwttoken; private string connected; private string jsonString;

    public string @errmsg="";

    private ACTIVITY submitActivity { get; set; } = new();

    List<Questionpin> Questions = new List<Questionpin>();

    List<Questionpin> res;

      List<Questionpin> list1 = new List<Questionpin>()

        {

            new Questionpin(){Id = 1, Pinnum = 20120605 },

            new Questionpin(){Id = 2, Pinnum= 20240815}

        };

    public class Questionpin

    {

        public long Id { get; set; }

        public int  Pinnum { get; set; }

    }

    public class ACTIVITY

    {

        public string Dummy { get; set; }

    }

    private async void Submit()

    {

        var jsonContent = new StringContent(JsonConvert.SerializeObject(new

        {

            bodyField1 = ""

        }), Encoding.UTF8, "application/json");

         connected = "N";

        using (var client1 = new HttpClient())

        {

            string authurl = "https://myquizapi.azurewebsites.net/api/";

            client1.BaseAddress = new Uri(authurl);

            client1.DefaultRequestHeaders.Clear();

            client1.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

            HttpResponseMessage Res = await client1.PostAsync("Auth", jsonContent);

            if (Res.IsSuccessStatusCode)

            {

                //Storing the response details recieved from web api

                string json = await Res.Content.ReadAsStringAsync();

                // Parse the JSON response to extract the address

                dynamic data1 = Newtonsoft.Json.JsonConvert.DeserializeObject(json);

                jwttoken = data1.token;

            }

        }

        string apiUrl = "https://myquizapi.azurewebsites.net/api/";

try

{ 

        using (HttpClient client = new HttpClient())

        {

            client.BaseAddress = new Uri(apiUrl);

            client.DefaultRequestHeaders.Clear();

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

            client.DefaultRequestHeaders.Add("Authorization", $"Bearer {jwttoken}");

            HttpResponseMessage response = null;

            response = await client.GetAsync("pins");

            // Check if the request was successful (status code 200)

            if (response.IsSuccessStatusCode)

            {

                // Make a GET request to the API

                connected = "Y";

                // Read the content of the response

                string jsonString = await response.Content.ReadAsStringAsync();

                // Deserialize the JSON string into an object

                Questions = JsonConvert.DeserializeObject<List<Questionpin>>(jsonString);

            }

            else{ Questions = list1;}

        }

}

catch(Exception ex)

{ if (connected == "N")

                {

                    Questions = list1;

                }}

        var result = Questions.FirstOrDefault(c => c.Pinnum == pin);

        if (result == null)

        {

            errmsg = "Enter Valid  pin";

        }

        else

        { Navigation.NavigateTo("/NewNav", true); }

    }

}

提前致谢

此问题整理于：https://learn.microsoft.com/en-us/answers/questions/1883475/code-exiting-when-offline-not-able-to-capture-exce

Answer 1

你好，

对于这个问题，可以使用 Maui 提供的 Connectivity 接口，在调用 HTTP 接口之前，先做一次连接判断。

请参考以下代码和文档：

private async void Submit()
{
    if(Connectivity.Current.NetworkAccess == NetworkAccess.Internet) // If the network is Internet state, then proceed with the following code
    {
        var jsonContent = new StringContent(JsonConvert.SerializeObject(new
        {
            bodyField1 = ""
        }), Encoding.UTF8, "application/json");
        connected = "N";
        using (var client1 = new HttpClient())
        {
            string authurl = "https://myquizapi.azurewebsites.net/api/";
            client1.BaseAddress = new Uri(authurl);
            client1.DefaultRequestHeaders.Clear();
            client1.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
            HttpResponseMessage Res = await client1.PostAsync("Auth", jsonContent);
            if (Res.IsSuccessStatusCode)
            {
                //Storing the response details recieved from web api
                string json = await Res.Content.ReadAsStringAsync();
                // Parse the JSON response to extract the address
                dynamic data1 = Newtonsoft.Json.JsonConvert.DeserializeObject(json);
                jwttoken = data1.token;
            }
        }
        string apiUrl = "https://myquizapi.azurewebsites.net/api/";
        try
        {
            using (HttpClient client = new HttpClient())
            {
                client.BaseAddress = new Uri(apiUrl);
                client.DefaultRequestHeaders.Clear();
                client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
                client.DefaultRequestHeaders.Add("Authorization", $"Bearer {jwttoken}");
                HttpResponseMessage response = null;
                response = await client.GetAsync("pins");
                // Check if the request was successful (status code 200)
                if (response.IsSuccessStatusCode)
                {
                    // Make a GET request to the API
                    connected = "Y";
                    // Read the content of the response
                    string jsonString = await response.Content.ReadAsStringAsync();
                    // Deserialize the JSON string into an object
                    Questions = JsonConvert.DeserializeObject<List<Questionpin>>(jsonString);
                }
                else { Questions = list1; }
            }
        }
        catch (Exception ex)
        {
            if (connected == "N")
            {
                Questions = list1;
            }
        }
        var result = Questions.FirstOrDefault(c => c.Pinnum == pin);
        if (result == null)
        {
            errmsg = "Enter Valid  pin";
        }
        else
        { Navigation.NavigateTo("/NewNav", true); }
    }
    else
    {
        Console.WriteLine("No Internet");
    }
}

• Connectivity.

---

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