private void FilterFormLoad(object sender, EventArgs e) { OnDropDownList.DataSource = Enum.GetValues(typeof(FilterKeyEnum)); OperatorDropDownList.DataSource = Enum.GetValues(typeof(FilterOperatorEnum)); OnDropDownList.Enabled = false; OperatorDropDownList.Enabled = false; ValueTextBox.Enabled = false; RemoveButton.Enabled = false; ApplyButton.Enabled = false; FiltersTreeView.Nodes.Clear(); FiltersTreeView.Nodes.AddRange(TreeNodeMapper.MapFilters(_filters)); }