fix #1095 Allow extending the rich text editor with more commands

Author: vegegoku

domino-ui/src/main/java/org/dominokit/domino/ui/richtext/RichTextActions.java

@@ -53,7 +53,7 @@
 import org.dominokit.domino.ui.richtext.commands.UnderLineCommand;
 import org.dominokit.domino.ui.richtext.commands.UndoCommand;
 
-public enum RichTextActions {
+public enum RichTextActions implements RichTextActionsGroup {
   COPY_PASTE(
       editor ->
           ButtonsGroup.create()

domino-ui/src/main/java/org/dominokit/domino/ui/richtext/RichTextActionsGroup.java

@@ -0,0 +1,21 @@
+/*
+ * Copyright © 2019 Dominokit
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.dominokit.domino.ui.richtext;
+
+import java.util.function.Function;
+import org.dominokit.domino.ui.IsElement;
+
+public interface RichTextActionsGroup extends Function<RichTextEditor, IsElement<?>> {}

domino-ui/src/main/java/org/dominokit/domino/ui/richtext/RichTextEditor.java

@@ -80,7 +80,7 @@ public static RichTextEditor create() {
    * @param actions A list of actions to be added to the editor toolbars.
    * @return a new instance of {@link RichTextEditor}
    */
-  public static RichTextEditor create(RichTextActions... actions) {
+  public static RichTextEditor create(RichTextActionsGroup... actions) {
     return new RichTextEditor(actions);
   }
 
@@ -90,7 +90,7 @@ public static RichTextEditor create(RichTextActions... actions) {
    * @param actions A list of actions to be added to the editor toolbars.
    * @return a new instance of {@link RichTextEditor}
    */
-  public static RichTextEditor create(Collection<RichTextActions> actions) {
+  public static RichTextEditor create(Collection<RichTextActionsGroup> actions) {
     return new RichTextEditor(actions);
   }
 
@@ -99,7 +99,7 @@ public static RichTextEditor create(Collection<RichTextActions> actions) {
    *
    * @param actions A list of actions to be added to the editor toolbars.
    */
-  public RichTextEditor(RichTextActions... actions) {
+  public RichTextEditor(RichTextActionsGroup... actions) {
     this(Arrays.asList(actions));
   }
 
@@ -113,7 +113,7 @@ public RichTextEditor() {
    *
    * @param actions A list of actions to be added to the editor toolbars.
    */
-  public RichTextEditor(Collection<RichTextActions> actions) {
+  public RichTextEditor(Collection<RichTextActionsGroup> actions) {
     this.root =
         div()
             .addCss(dui_rich_text)