How to bind a list count to a label in WinForms?

Question

How can I bind the count of a list to a label. The following code does't get updated with the list is changed:

private IList<string> list = new List<string>();
//...
label1.DataBindings.Add("Text", list.Count, "");

Answer 1

Bindings listen to the PropertyChanged event of the IPropertyChanged interface. I don't think that List.Count is reported as a PropertyChanged event when it is changed.

What you could do is to implement your custom List or to find a collection that notifies when the Count is changed.

Answer 2

You can use DataSourceChanged if you have a datasource for the listbox. Just remember to update and rebind the datasource.

This may be a bit ghetto but here is the example I worked with:

List<int> collection = new List<int>();
    public Form1()
    {
        InitializeComponent();
        listBox1.DataSourceChanged += listbox1_Changed;
    }

    private void button1_Click(object sender, EventArgs e)
    {
        collection.Add(new Random().Next(100));
        listBox1.BeginUpdate();
        listBox1.DataSource = null;
        listBox1.DataSource = collection;
        listBox1.EndUpdate();
    }
    private void listbox1_Changed(object sender, EventArgs e)
    {
        textBox1.Text = collection.Count.ToString();
    }

Answer 3

According to Marc Gravell for this problem, he has suggested to create a facade that wraps the collection you want to bind to label1.Text

I have tried to implement one (for fun) and was able to get binding to Count working.
CountList<T> is a facade that wraps a collection to bind to.

Here is the full of the demo.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Windows.Forms;

namespace TextBindingTest
{
    public partial class Form1 : Form
    {
        private readonly CountList<string> _List =
            new CountList<string>(new List<string> { "a", "b", "c" });

        public Form1()
        {
            InitializeComponent();
            BindAll();
        }

        private void BindAll()
        {
            var binding = new Binding("Text", _List, "Count", true);
            binding.Format += (sender, e) => e.Value = string.Format("{0} items", e.Value);
            label1.DataBindings.Add(binding);
        }

        private void addToList_Click(object sender, EventArgs e)
        {
            _List.Add("a");
        }

        private void closeButton_Click(object sender, EventArgs e)
        {
            Close();
        }
    }

    public class CountList<T> : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged = delegate { };
        private void OnPropertyChanged(PropertyChangedEventArgs e)
        {
            var handler = PropertyChanged;
            handler(this, e);
        }

        private ICollection<T> List { get; set; }
        public int Count { get { return List.Count; } }

        public CountList(ICollection<T> list)
        {
            List = list;
        }

        public void Add(T item)
        {
            List.Add(item);
            OnPropertyChanged(new PropertyChangedEventArgs("Count"));
        }
    }
}