ComboBox ItemsSource binding doesn't update with Observable Collection Add

Question

I have a simple wpf app, that I want to try to use ItemsSource binding from xaml. When I click the button. it should be updated also in the UI, but it doesn't.

Why doesn't it work?

Xaml code:

<Window x:Class="SendRawEthernetPacketsGUI.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="300" Width="300">
<Grid>
    <ComboBox HorizontalAlignment="Left" Margin="76,65,0,0" VerticalAlignment="Top" Width="120" ItemsSource="{Binding test}"/>
    <Button Content="Button" HorizontalAlignment="Left" Margin="90,171,0,0" VerticalAlignment="Top" Width="75" Click="Button_Click"/>

</Grid>

C# code:

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Shapes;

namespace SendRawEthernetPacketsGUI
{

/// <summary>
/// Interaction logic for Window1.xaml
/// </summary>
public partial class Window1 : Window
{
    public ObservableCollection<string> test = new ObservableCollection<string>();
    public Window1()
    {
        InitializeComponent();
        DataContext = this;
    }

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        test.Add("fdfddf");
    }
}
}

It feels kinda stupid to even ask this, but even looking in google didn't help me. So can you?

Answer 1

Your binding never worked in the first place. You can only bind to properties not fields .

Try this instead:

public ObservableCollection<string> test { get; set; }

public Window1()
{
    Test = new ObservableCollection<string>();
}

Or if you want some tricky C# 6 magic:

public ObservableCollection<string> test => new ObservableCollection<string>();

This is a function bodied-member and compiles to a read-only property that is initialized to the new ObservableCollection

Caveats/Design Errors:

Note that in both cases you aren't using INotifyPropertyChanged , so wholesale assignments to the collection won't be picked up by the UI. You should also be using PascalCase for your public properties, and using a proper view model instead of binding to the code-behind.