private void InternalEditorsInit()
        {
            _expressionEditor = new ConditionExpressionEditorControl(PrimaryStyleCollection.ColumnInfo);
            _expressionEditor.ExpressionChanged += delegate { UpdateExpressionString(); };

            var enabledBinding = new Binding(SelectedItemPropertyName)
            {
                Converter = new InternalStateConverter()
            };

            _expressionEditor.SetBinding(IsEnabledProperty, enabledBinding);
            expressionGroup.Children.Add(_expressionEditor);
        }
 private void OnClosed(object sender, EventArgs e)
 {
     Closed           -= OnClosed;
     _expressionEditor = null;
 }