Setting ComboBox DataSource to an enum and binding SelectedValue

Question

I am kinda desperate, because yesterday it was working but today this is not working anymore, let me explain, what I am trying to do:

I want to set the DataSource of a ComboBox to all enum values in a specific enum. Just like that:

cmbType.DataSource = m_addViewPresenter.Types;

where Types is a BindingList and is being initialised like that:

public BindingList<MyEnum> Types
{
    get { return m_types; }
    set
    {
        m_types = value;
        OnPropertyChanged();
    }
}

[ImportingConstructor]
public AddViewPresenter()
{
    Types = new BindingList<MyEnum>(
              Enum.GetValues(typeof(MyEnum))
                         .Cast<MyEnum>().ToList());
}

Further more, I want to bind the current item selected to a property. Since ComboBox.SelectedItem doesn't fire a INotifyProperty-event, I am using ComboBox.SelectedValue.

cmbType.Bind(m_addViewPresenter, c => c.SelectedValue, m => m.SelectedValue);

public static void Bind<TComponent, T>(
    this TComponent component, T value,
    Expression<Func<TComponent, object>> controlProperty, 
    Expression<Func<T, object>> modelProperty)
    where TComponent : IBindableComponent
    where T : INotifyPropertyChanged
{
    var controlPropertyName = PropertyNameResolver.GetPropertyName(controlProperty);
    var modelPropertyName = PropertyNameResolver.GetPropertyName(modelProperty);
    component.DataBindings.Add(new Binding(controlPropertyName, value, modelPropertyName, false, DataSourceUpdateMode.OnPropertyChanged));
}

It worked fine yesterday, but something messed things up and today I am only getting an InvalidOperationException:

Cannot set the SelectedValue in a ListControl with an empty ValueMember.

I know it's digging in the dark, but can anyone brainstorm with me and find out, what's the problem? Thanks in advance!

Looks like binding to `ComboBox.SelectedValue` requires setting 'ComboBox.ValueMember` — Ivan Stoev, Oct 07 '15 at 17:08
You should really bind to `ComboBox.SelectedItem`, I don't know why do you think it will not fire property change notification, I think it does. — Ivan Stoev, Oct 07 '15 at 17:12
I tried it with cmbType.Bind(m_addViewPresenter, c => c.SelectedValue, m => m.SelectedValue);, but it wasnt going into the setter. :/ — Jannik, Oct 07 '15 at 17:17
@Jannik To use data binding to `SelectedValue`, use another class that contains a property as `DisplayMember` and a property as `ValueMember` and shape your enum values to a `List` as `DataSourec`, or simplye use your enum values as data source and bind to `SelectedItem` as mentioned by Ivan too. — Reza Aghaei, Oct 07 '15 at 17:26
Like I told you, binding SelectedItem is not going into the setter of SelectedValue, it is not working. — Jannik, Oct 07 '15 at 17:36
@Jannik Sorry, I was pretty sure there is `SelectedItemChanged` event, in in fact it exists internally, but they forgot to expose it! `SelectedValue` is fine, as soon as you don't need two way binding (i.e, from your class property to combobox) in which case it throws the exception you are getting. — Ivan Stoev, Oct 07 '15 at 17:36
@IvanStoev It works for `SelectedItem` too. I bind my object property to it and checked the value after selecting new item in combobox, the new value had been set in my object property. — Reza Aghaei, Oct 07 '15 at 17:40

Reza Aghaei · Accepted Answer · 2015-10-07T18:15:22.667

Option 1

To use SelectedValue for data binding, Create a calss DataItem:

public class DataItem
{
    public MyEnum Value { get; set; }
    public string Text { get; set; }
}

Then use this code for data binding:

this.comboBox1.DataSource = Enum.GetValues(typeof(MyEnum)).Cast<MyEnum>()
                                .Select(x => new DataItem() { Value = x, Text = x.ToString() })
                                .ToList();
this.comboBox1.ValueMember = "Value";
this.comboBox1.DisplayMember = "Text";

this.comboBox1.DataBindings.Add(
    new Binding("SelectedValue", yourObjectToBind, "PropertyOfYourObject"));

You can make generic DataItem<T> containing public T Value { get; set; } to make it more reusable in your project.

Option 2

To Use SelectedItem for data binding:

this.comboBox1.DataSource = Enum.GetValues(typeof(MyEnum));
this.comboBox1.DataBindings.Add(
    new Binding("SelectedItem", yourObjectToBind, "PropertyOfYourObject"));

Option 3

To use SelectedValue for data binding as another option suggested by Ivan Stoev, you can perform data to binding this way:

this.comboBox1.DataSource = Enum.GetValues(typeof(MyEnum));
this.comboBox1.DataBindings.Add(
    new Binding("SelectedValue", yourObjectToBind, "PropertyOfYourObject",
                true,  DataSourceUpdateMode.OnPropertyChanged));

Edit by Jannik:

The basic generic approach of option 1 would look like this:

public class ComboBoxItemWrapper<T>
{
    public T Value { get; set; }
    public string Text { get; set; }
}

Its working fine, its a bit annoying you need a wrapping class though. — Jannik, Oct 07 '15 at 17:48
@Jannik Thank you for accepting the answer, you can make the class more reusable by making it `Generic` then it will be less annoying, or probably be lovely. — Reza Aghaei, Oct 07 '15 at 17:54
@Jannik you are welcome, I edited the answer and mentioned generics, hope you find it helpful:) — Reza Aghaei, Oct 07 '15 at 18:03
Damn, I edited the answer aswell and added the generic approach :D — Jannik, Oct 07 '15 at 18:04
Options 1 and 2, including the generic approach, are functioning well, thanks. Option 3 is not working, at least nowadays (VS 2022 with WinForms !!!) — Marcelo Scofano Diniz, Jan 24 '22 at 03:14

score 3 · Answer 2 · edited May 23 '17 at 12:29

Ok, here is the case. You are correctly binding to ComboBox.SelectedValue. The problem is coming from the following line:

component.DataBindings.Add(new Binding(controlPropertyName, value, modelPropertyName, false, DataSourceUpdateMode.OnPropertyChanged));

It should be

component.DataBindings.Add(new Binding(controlPropertyName, value, modelPropertyName, true, DataSourceUpdateMode.OnPropertyChanged));

Shortly, always set Binding.FormattingEnabled to true (as in my example answering another question by you) when using WF data binding and you'll have no problems.

A modified example from my answer to Exchange UserControls on a Form with data-binding showing the case and the solution:

using System;
using System.Drawing;
using System.Windows.Forms;

namespace Tests
{
    enum MyEnum {  Red, Green, }
    class Controller
    {
        public MyEnum SelectedValue { get; set; }
    }
    static class Program
    {
        [STAThread]
        static void Main()
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            var form = new Form();
            var topPanel = new Panel { Dock = DockStyle.Top, Parent = form };
            var combo = new ComboBox { Left = 8, Top = 8, Parent = topPanel };
            topPanel.Height = combo.Height + 16;
            combo.DataSource = (MyEnum[])Enum.GetValues(typeof(MyEnum));
            var c = new Controller();
            combo.DataBindings.Add(new Binding("SelectedValue", c, "SelectedValue", true, DataSourceUpdateMode.OnPropertyChanged));
            form.BindingContextChanged += (sender, e) =>
            {
                // If you change combo binding formatting enabled parameter to false,
                // the next will throw the exception you are getting
                c.SelectedValue = MyEnum.Red;
            };
            var panel1 = new Panel { Dock = DockStyle.Fill, Parent = form, BackColor = Color.Red };
            var panel2 = new Panel { Dock = DockStyle.Fill, Parent = form, BackColor = Color.Green };
            Bind(panel1, "Visible", combo, "SelectedValue", value => (MyEnum)value == MyEnum.Red);
            Bind(panel2, "Visible", combo, "SelectedValue", value => (MyEnum)value == MyEnum.Green);
            Application.Run(form);
        }
        static void Bind(Control target, string targetProperty, object source, string sourceProperty, Func<object, object> expression)
        {
            var binding = new Binding(targetProperty, source, sourceProperty, false, DataSourceUpdateMode.Never);
            binding.Format += (sender, e) => e.Value = expression(e.Value);
            target.DataBindings.Add(binding);
        }
    }
}

You may also find useful the following thread Custom WinForms data binding with converter not working on nullable type (double?)

To make answer more complete, I added a data binding option this way to the answer, and mentioned you in answer. +1 — Reza Aghaei, Oct 07 '15 at 18:16
@RezaAghaei: Than you, you have my +1 too (as we seems to be one of the last WF mohicans :-) — Ivan Stoev, Oct 07 '15 at 18:21

Setting ComboBox DataSource to an enum and binding SelectedValue

2 Answers2