null reference exception when i delete item from sync realm database in xamarin

Question

enter image description here I got a null reference exception after I delete any item from the sync realm database . the item is deleted from the database but it throws the exception and craches I don't know why it throws this exception or where is the null object .

but when I delete this line the exception disappears : listView.ItemsSource = Employees;

PS : this exception appeared when I tried to sync the realm database online.

public MainPage()
    {
        InitializeComponent();
        Initialize();
        listView.ItemsSource = Employees;
    }    
private async Task Initialize()
    {
        _realm = await OpenRealm();
        Employees = _realm.All<Employee>();
        Entertainments= _realm.All<Entertainment>();
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Employees)));
    }

void OnDeleteClicked(object sender, EventArgs e)
    {
        try {
            var o = _realm.All<Employee>().FirstOrDefault(c => c.EmpId == 4);
            if (o != null)
                _realm.Write(() => { _realm.Remove(o); });
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Employees)));
        }
        catch (Exception exp)
        {
            string msg = exp.Message;
        }

    }

here is a screenshot of the exception

https://learn.microsoft.com/en-us/visualstudio/mac/debugging?view=vsmac-2019 — Jason, Jun 19 '19 at 15:27
There is your problem. Please, use a ObservableCollection so you can dynamically add or remove items binded to the listview — Bruno Caceiro, Jun 19 '19 at 16:21
that would not cause a null ref. The stack trace of the exception object should tell you which line causes the exception — Jason, Jun 19 '19 at 16:45
@Saamer I added a screenshot for the exception now , thank you . — maria nabil, Jun 19 '19 at 19:50
@BrunoCaceiro THIS SOLVED THE EXCEPTION ! Thank youu . but the listview is not auto updated now ! — maria nabil, Jun 19 '19 at 19:52
Possible duplicate of [What is a NullReferenceException, and how do I fix it?](https://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-and-how-do-i-fix-it) — Stefan, Jun 19 '19 at 19:54
@Jason I have debugged but the debugger didn't tell me which line causes the exception , instead it jump to the exception in the screenshot here : https://i.stack.imgur.com/x9iOY.png — maria nabil, Jun 19 '19 at 19:54

score 0 · Accepted Answer · answered Jun 20 '19 at 02:24

THIS SOLVED THE EXCEPTION ! Thank youu . but the listview is not auto updated now !

According to your code and description, you want to delete item form realm database, and update Listview. I find you use PropertyChanged to want to update Employees, but it doesn't work, because you delete item from realm database, don't change Employees, so it is not fired PropertyChanged event.

 List<Employee> Employees = new List<Employee>();
    private async Task Initialize()
    {
        _realm = await OpenRealm();
        Employees = _realm.All<Employee>().ToList(); ;
        Entertainments = _realm.All<Entertainment>();

    }
    void OnDeleteClicked(object sender, EventArgs e)
    {
        try
        {
            var o = _realm.All<Employee>().FirstOrDefault(c => c.EmpId == 4);
            if (o != null)
                _realm.Write(() => { _realm.Remove(o); });
            Employees = _realm.All<Employee>().ToList();
            listView.ItemsSource = Employees;
        }
        catch (Exception exp)
        {
            string msg = exp.Message;
        }

    }

Helpful article for you: https://dzone.com/articles/xamarinforms-working-with-realm-database

null reference exception when i delete item from sync realm database in xamarin

1 Answers1