Code Exiting when Offline not able to capture exception

Question

This code works perfectly in online, when offline not connected to internet , I want to assign static pins but this code is exiting and not loading Questions with list1.

Exception thriow

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); }
    }
 
}

Answer 1

Hello,

For this problem, you can use the Connectivity interface provided by Maui to make a connection judgment before calling the HTTP interface.

Please refer to the following code and documentation:

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

Best Regards,

Alec Liu.

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