namespace Wnd public partial class ButtonTextBox UserControl Browsable

namespace Wnd
{
    public partial class ButtonTextBox : UserControl
    {
        [Browsable(true), DesignerSerializationVisibility(DesignerSerializationVisibility.Visible)]
        public event EventHandler ButtonClick;

        [DefaultValue(false)]
        public bool ReadOnly
        {
            get { return _ReadOnly; }
            set
            {
                _ReadOnly = value; 
                OnReadOnlyChanged();
            }
        }
        private bool _ReadOnly;
        

        public ButtonTextBox()
        {
            InitializeComponent();
        }

        private void btnButton_Click(object sender, EventArgs e)
        {
            if(ButtonClick != null) // если кто-то подписался!!!
               ButtonClick(sender, e);
        }

        protected virtual void OnReadOnlyChanged()
        {
            txtText.BackColor = ReadOnly ? SystemColors.Info : SystemColors.Window; // не забудь вернуть Window!!!
        }
    }
}