public partial class Form1 : Form
{
    private Foo _foo;

    public Form1()
    {
        InitializeComponent();
    }

    private void button1_Click(object sender, EventArgs e)
    {
        button1.Enabled = false;
        _foo = new Foo();
        BindingSource bs = new BindingSource(components);
        bs.DataSource = _foo;

        textBox1.DataBindings.Add("Text", bs, "Name", true, DataSourceUpdateMode.OnValidation);
        textBox1.Validating += new CancelEventHandler(textBox1_Validating);
        textBox1.Leave += new EventHandler(textBox1_Leave);
        textBox1.DataBindings["Text"].Format += new ConvertEventHandler(textBox1_Format);
        textBox1.DataBindings["Text"].Parse += new ConvertEventHandler(textBox1_Parse);
    }

    void textBox1_Leave(object sender, EventArgs e)
    {
        System.Diagnostics.Debug.Print("Leave textBox1");
    }

    void textBox1_Parse(object sender, ConvertEventArgs e)
    {
        System.Diagnostics.Debug.Print("Parse textBox1");
    }

    void textBox1_Format(object sender, ConvertEventArgs e)
    {
        System.Diagnostics.Debug.Print("Format textBox1");
    }

    void textBox1_Validating(object sender, CancelEventArgs e)
    {
        System.Diagnostics.Debug.Print("Validating textBox1");
    }

    private void button3_Click(object sender, EventArgs e)
    {
        System.Diagnostics.Debug.Print("textBox1.Text = {0}", textBox1.Text);
        System.Diagnostics.Debug.Print("Foo.Name = {0}", _foo.Name);
    }
}

public class Foo : IDataErrorInfo
{
    private string _error;
    private Dictionary<string, string> _errors;
    private string _name;

    public Foo()
    {
        _error = String.Empty;
        _errors = new Dictionary<string, string>();
        _errors["Name"] = String.Empty;
    }

    public string[] AvailableNames
    {
        get
        {
            if (_availableNames == null)
            {
                _availableNames = new string[] {
                    "John", "Jeff", "Elton", "Bar", "Robert" };
            }
            return _availableNames;
        }
    }
    private string[] _availableNames;

    public string Name
    {
        get { return _name; }
        set
        {
            _name = value;
            if (!String.IsNullOrEmpty(_name) && !String.Equals(_name, "Bar", StringComparison.CurrentCultureIgnoreCase))
                _errors["Name"] = "That name isn't right.";
            else
                _errors["Name"] = String.Empty;
            if (NameChanged != null)
                NameChanged(this, EventArgs.Empty);
        }
    }

    public event EventHandler NameChanged;

    #region IDataErrorInfo Members

    public string Error
    {
        get { return _error; }
    }

    public string this[string columnName]
    {
        get { return _errors[columnName]; }
    }

    #endregion
}

[EditorBrowsable(EditorBrowsableState.Advanced)]
protected virtual void OnValidating(CancelEventArgs e)
{
    CancelEventHandler handler = (CancelEventHandler) base.Events[EventValidating];
    if (handler != null)
    {
        handler(this, e);
    }
}