Changing Itemsources Object doesnt change Listbox (C# WPF)

Question

I hope my title isnt too misleading, but heres a quick explanation. As mentioned in the title im using WPF and I set the Itemsources of a Listbox to an ObservableCollection. I also made a DataTemplate for it to show the values correctly. However my problem is that when im changing the values in the ObservableCollection it doesnt show in the listbox. The question is now, what am I doing wrong?

Heres the code:

public ObservableCollection<Employee> employees;
employees = DatabaseControl.GetEmployees();
Employee_ComboBox.ItemsSource = employees;

Then im switching out the whole Collection:

private void save_Employee_Click(object sender, RoutedEventArgs e)
    {
        deactivateEmployee();
        if (isnewEmployee)
        {
            DatabaseControl.AddEmployee(employee_firstName.Text, employee_lastName.Text, employee_phoneNumber.Text, employee_city.Text, employee_address.Text);
            isnewEmployee = false;
        }
        if (updateEmployee)
        {
            DatabaseControl.UpdateEmployee(((Employee)Employee_ComboBox.SelectedItem).ID, employee_firstName.Text, employee_lastName.Text, employee_phoneNumber.Text, employee_city.Text, employee_address.Text);
            updateEmployee = false;
        }
        employees = DatabaseControl.GetEmployees();
        Employee_ComboBox.ItemsSource = employees;
    }

But this doesnt seem to work out as it should. So what am I doing wrong here? GetEmpoyees() returns an ObservableCollection btw.

score 1 · Accepted Answer · answered Jul 10 '16 at 18:44

The point of the ObservableCollection<Employee> is that when you bind to it then the UI will react when you add/remove items from it, but right now you are adding items to another instance. If you don't want to change your design too much then I would suggest having the DatabaseControl.GetEmployees() return an IList and put the result into the employees ObservableCollection

A simple approach that works well for not too many employees, but may perform poorly if you have many thousands of employees is to clear and add all

IList<Employee> result = DatabaseControl.GetEmployees();
employees.Clear();
foreach (Employee employee in result)
{
    employees.Add(employee);
}

A more clean design IMHO would be to instead create an Employee instance outside of your DatabaseControl and then both send that to the DatabaseControl and add it to the employees collection.

Also - you may want to consider using a ViewModel with an ICommand Save and a property ObservableCollection<Employee> {get; private set;} and binding to those from your view.

There are very few Employees so I used your solution. Which is working out great for me. Thank you. — Patrick, Jul 12 '16 at 10:07

score 0 · Answer 2 · answered Jul 10 '16 at 17:02

0

If the employees collection is the same, then the combobox will not see any change. Therefore first assign null to the items source:

Employee_ComboBox.ItemsSource = null;
Employee_ComboBox.ItemsSource = employees;

answered Jul 10 '16 at 17:02

Olivier Jacot-Descombes

104,806
13
138
188

This is not the problem, because if it was the same collection, listbox would be updated immediatelly as the item was added to the collection – Liero Jul 10 '16 at 17:26
Its not really the same. Im picking an item of the combobox, getting the id of it, changing the values of the record with this id, updating the database and then reload all the employees in the employees Collection. But its not showing the changes, neither in the combobox nor in the textboxes showing the values of the records. – Patrick Jul 10 '16 at 17:27
And yes the values get changed in the database. – Patrick Jul 10 '16 at 17:27
I have no idea what `DatabaseControl` is, but could it return a cached entry instead of reloading it from the db? – Olivier Jacot-Descombes Jul 10 '16 at 17:49

score 0 · Answer 3 · answered Jul 10 '16 at 17:41

0

Considering you are not using bindings, have you tried:

Employee_ComboBox.InvalidateVisual();

Hope it helps!

answered Jul 10 '16 at 17:41

Itay Podhajcer

2,616
2
9
14

Changing Itemsources Object doesnt change Listbox (C# WPF)

3 Answers3