Reset Combobox internal state (#11412)

issue in #11343 and #11385 is not reproducible on top this patch
Three different bugs are involved in this fix:
we bring the old fix(#11094) back and fixed the other related issues:
1) allow adding the same new item after dataProvider got reset, This is cause by the client side parameter `LastNewItemString`, it saves the value added before resetting. 
2) clear the pending newItem eagerly, so that the same value will not be added again.

1 files changed, 11 insertions, 3 deletions

diff --git a/server/src/main/java/com/vaadin/ui/ComboBox.java b/server/src/main/java/com/vaadin/ui/ComboBox.java
index a976782ecc..8fadca6c35 100644
--- a/server/src/main/java/com/vaadin/ui/ComboBox.java
+++ b/server/src/main/java/com/vaadin/ui/ComboBox.java
@@ -191,6 +191,15 @@ public class ComboBox<T> extends AbstractSingleSelect<T>
                 if (getNewItemProvider() != null) {
                     Optional<T> item = getNewItemProvider().apply(itemValue);
                     added = item.isPresent();
+                    // Fixes issue https://github.com/vaadin/framework/issues/11343
+                    // Update the internal selection state immediately to avoid
+                    // client side hanging. This is needed for cases that user
+                    // interaction fires multi events (like adding and deleting)
+                    // on a new item during the same round trip.
+                    item.ifPresent(value -> {
+                        setSelectedItem(value, true);
+                        getDataCommunicator().reset();
+                    });
                 } else if (getNewItemHandler() != null) {
                     getNewItemHandler().accept(itemValue);
                     // Up to the user to tell if no item was added.
@@ -446,7 +455,7 @@ public class ComboBox<T> extends AbstractSingleSelect<T>
      * @since 8.0
      */
     public void setDataProvider(CaptionFilter captionFilter,
-            ListDataProvider<T> listDataProvider) {
+                                ListDataProvider<T> listDataProvider) {
         Objects.requireNonNull(listDataProvider,
                 "List data provider cannot be null");
 
@@ -610,12 +619,11 @@ public class ComboBox<T> extends AbstractSingleSelect<T>
      * <p>
      * The empty string {@code ""} is the default empty selection caption.
      *
+     * @return the empty selection caption, not {@code null}
      * @see #setEmptySelectionAllowed(boolean)
      * @see #isEmptySelectionAllowed()
      * @see #setEmptySelectionCaption(String)
      * @see #isSelected(Object)
-     *
-     * @return the empty selection caption, not {@code null}
      * @since 8.0
      */
     public String getEmptySelectionCaption() {