System.ArgumentNullException: 'Value cannot be null. Parameter name: item' xamarin.forms

Question

i have a page with a collection view that lists the students at a school. when i select a student i should get the data about this student. the thing is that when i select the student i get this exception:

**System.ArgumentNullException:** 'Value cannot be null.
Parameter name: item'

the problem is that it was working well. when i made some changes to other pages and added some new pages, the error emerged. moreover, i inserted a break point at the line where i select a student to check if the values are null, but the result was that they had values. and this confused me.

this is the code of my xaml.cs page:

  HttpClient client = new HttpClient();
        List list_total_reg_std = new List();
        List list_filtered_reg_std = new List();
        bool filtered = false;
        string year_id = "";
        string pro = "";
        public Accounting()
        {
            InitializeComponent();
            
            imgAdd.Source = ImageSource.FromResource("ALNahrainAlphaApp.icons.add_col.png");
            imgfilter.Source = ImageSource.FromResource("ALNahrainAlphaApp.icons.filter_ic.png");
            imgshare.Source = ImageSource.FromResource("ALNahrainAlphaApp.icons.share_icon.png");
           
            year_id = Preferences.Get("AcademicYearId","");
            if (Preferences.Get("permission", "")== "Nursery & kgs")
            {
                pro = "GetAllregstdsForKgs";
            }
            else
            {
                pro = "GetAllregstds";
            }
           
            loaddata();
            var AddTap = new TapGestureRecognizer();
            AddTap.Tapped += async (sender, e) =>
            {
                var stack = this.Navigation.NavigationStack;
                if (stack[stack.Count - 1].GetType() != typeof(RegisterNewStd))
                {
                    await Navigation.PushAsync(new RegisterNewStd());
                }
            };
            stckAddStd.GestureRecognizers.Add(AddTap);
            
            ICommand refreshCommand = new Command(() =>
            {
               if(refresh.IsRefreshing)
                {
                    loaddata();
                }
                    
                refresh.IsRefreshing = false;
            });
            refresh.Command = refreshCommand;

            var FilterTap = new TapGestureRecognizer();
            FilterTap.Tapped += FilterTap_Tapped;
            stckfilter.GestureRecognizers.Add(FilterTap);
            
            
        }
    async private void loaddata()
        {
            popupLoadingView.IsVisible = true;
            activityIndicator.IsRunning = true;

            urlClass urldata = new urlClass();
            string uri = urldata.url + "/"+pro+"/"+year_id;
            list_total_reg_std.Clear();
          
            try
            {

                HttpResponseMessage response = await client.GetAsync(uri);

                if (response.IsSuccessStatusCode == true)
                {
                    string content = await response.Content.ReadAsStringAsync();
                    list_total_reg_std = JsonConvert.DeserializeObject>(content);
                    popupLoadingView.IsVisible = false;
                    activityIndicator.IsRunning = false;
                    registeredstdslist.ItemsSource = list_total_reg_std;
                    foreach (var registered in list_total_reg_std)
                    {
                        if (string.IsNullOrEmpty(registered.ExpectedDateofPayment))
                        {
                            registered.ExpectedDateofPayment = "...";
                        }
                        if (registered.ExpectedDateofPayment == DateTime.Today.ToString("dd/MM/yyyy"))
                            registered.status = 1;
                        else if(  DateTime.Today== DateTime.ParseExact(registered.ExpectedDateofPayment, "dd/MM/yyyy", null).AddDays(-5))
                            registered.status = 2;
                        else
                            registered.status = 0;

                      
                        if (registered.Dateofpayment == DateTime.Today.ToString("dd/MM/yyyy"))
                            registered.payedtoday = true;
                      
                        else
                            registered.payedtoday = false;

                    }

                }
                else
                {
                    await DisplayAlert("Operation Failed", "Response Failed!", "Cancel");
                }

            }
            catch (System.Net.WebException exp)
            {
                bool ans = await DisplayAlert("Connection Failed", "Please Check Your Internet Connection!", "Retry", "Cancel");
                if (ans == true)
                    loaddata();
            }
            catch (Exception exp)
            {
                bool ans = await DisplayAlert("Connection Failed", exp.Message, "Retry", "Cancel");
                if (ans == true)
                    loaddata();
            }
        }
 async private void registeredstdslist_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            registeredstdinfo selecteditem= registeredstdslist.SelectedItem as registeredstdinfo;
            await Navigation.PushAsync(new stdregisteredDetails(selecteditem.stdid,selecteditem.name,selecteditem.edlevel));
        }
}

this is were i select a student:

async private void registeredstdslist_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            registeredstdinfo selecteditem= registeredstdslist.SelectedItem as registeredstdinfo;
            await Navigation.PushAsync(new stdregisteredDetails(selecteditem.stdid,selecteditem.name,selecteditem.edlevel));
        }

this is the xaml page:

i can't figure out the reason. i removed the bin and obj folders, cleaned the solution then built it but still nothing, what should i do? thanks in advance.

System.ArgumentNullException: 'Value cannot be null. Parameter name: item' xamarin.forms

0 Answers