Sorry, now it works correctly. Perhaps I run a old version of the
application.

Thanks
Marco

Hi Marco,

It's a combination of things that is causing your TextBox to update late.

First, the default databinding behaviour is to update its underlying source once you validate the control for instance by leaving it.  Since you want the TextBox to gray out immediatly as you click the CheckBox you need to tell the databinding to update immediatly (see the code below on how to do this).

Second, since you bind two controls to the same property the second control won't get notified, and won't get updated until you cange the datasource by selecting another item or similar.  To fix this, Person needs to implement the INotifyPropertyChanged event, and fire an event every time this property is changed.  This is also true for any property you change programmatically (see the code below on how to implement and use INotifyPropertyChanged)

    public partial class Form2 : System.Windows.Forms.Form
    {

        public Form2()
        {
            InitializeComponent();
        }

        protected override void OnLoad(EventArgs e)
        {
            // You probably don't need a PersonList class
            BindingList<Person> personList = new BindingList<Person>();
            personList.Add(new Person("One"));
            personList.Add(new Person("Two"));
            personList.Add(new Person("Three"));

            // The ListBox will allow us to change persons and see the effect of setting ReadOnly
            listBox1.DataSource = personList;
            listBox1.DisplayMember = "Name";

            // Note the added parameters for the Checked property
            // Setting DataSourceUpdateMode.OnPropertyChanged means the Person will get updated immediatly.
            // This is also good on TextBoxes where you want to update something while you write.
            checkBox1.DataBindings.Add("Checked", personList, "ReadOnly", false, DataSourceUpdateMode.OnPropertyChanged);
            textBox1.DataBindings.Add("Text", personList, "Name");
            textBox1.DataBindings.Add("ReadOnly", personList, "ReadOnly");
        }
    }

    public class Person : INotifyPropertyChanged
    {
        private bool readOnly;

        public bool ReadOnly
        {
            get { return readOnly; }
            set
            {
                readOnly = value;
                // Fire a PropertyChanged event so the TextBox will get notified
                PropertyChanged(this, new PropertyChangedEventArgs("Locked"));
            }
        }

        private string name;

        public string Name
        {
            get { return name; }
            set { name = value; }
        }

        public Person(string name)
        {
            this.Name = name;
        }

        // This is the code added by SHIFT-ALT-F10 on INotifyPropertyChanged
        // All this interface does is declare a single event
        #region INotifyPropertyChanged Members

        public event PropertyChangedEventHandler PropertyChanged;

        #endregion
    }