interface IModify
    {
bool IsModified { get; }
    }

class TextBoxEx : TextBox, IModify
    {
private bool isModified = false;

public bool IsModified
        {
get { return isModified; }
        }

protected override void OnTextChanged(EventArgs e)
        {
this.isModified = true;
base.OnTextChanged(e);
        }
    }

        private void button1_Click(object sender, EventArgs e)
        {
var b = IsModify(this);
            Text = b.ToString();
        }

private bool IsModify(Control ctrl)
        {
foreach (Control control in ctrl.Controls)
            {
if (control.Controls.Count > 0)
return IsModify(control);
if (control is IModify)
                {
if (((IModify)control).IsModified)
return true;
                }
            }
return false;
        }