[WIP] feat: add protected refreshViewport method

flow-data/src/main/java/com/vaadin/flow/data/provider/DataCommunicator.java

@@ -436,6 +436,15 @@ public void refresh(T data) {
         requestFlushUpdatedData();
     }
 
+    /**
+     * Schedules a re-render of the items that are currently in the viewport to
+     * refresh their content with the latest data from the generators.
+     */
+    protected void refreshViewport() {
+        resendEntireRange = true;
+        requestFlush();
+    }
+
     /**
      * Confirm update with the given {@code updateId}.
      *

flow-data/src/main/java/com/vaadin/flow/data/provider/hierarchy/HierarchicalDataCommunicator.java

@@ -257,6 +257,11 @@ public void refresh(T item, boolean refreshChildren) {
         requestFlush().invalidateItem(item);
     }
 
+    @Override
+    protected void refreshViewport() {
+        requestFlush().invalidateViewport();
+    }
+
     @Override
     public Stream<T> fetchFromProvider(int offset, int limit) {
         return fetchDataProviderChildren(null, Range.withLength(offset, limit));

flow-data/src/test/java/com/vaadin/flow/data/provider/DataCommunicatorTest.java

@@ -57,6 +57,7 @@
 import com.vaadin.flow.server.VaadinServletService;
 import com.vaadin.flow.server.VaadinSession;
 
+import elemental.json.JsonObject;
 import elemental.json.JsonValue;
 
 @RunWith(Parameterized.class)
@@ -247,6 +248,33 @@ public void reattach_same_roundtrip_refresh_nothing() {
         Assert.assertNull("Expected no communication after reattach", lastSet);
     }
 
+    @Test
+    public void refreshViewport_updatedRangeSent() {
+        var compositeDataGenerator = new CompositeDataGenerator<Item>();
+        dataCommunicator = new DataCommunicator<>(compositeDataGenerator, arrayUpdater,
+                data -> {
+                }, element.getNode()) {
+        };
+        dataCommunicator.setDataProvider(createDataProvider(), null);
+        dataCommunicator.setViewportRange(0, 6);
+
+        var count = new AtomicInteger(0);
+        compositeDataGenerator.addDataGenerator(new DataGenerator<Item>() {
+            @Override
+            public void generateData(Item item, JsonObject json) {
+                json.put("count", String.valueOf(count.get()));
+            }
+        });
+
+        fakeClientCommunication();
+        Assert.assertEquals(Range.withLength(0, 6), lastSet);
+        lastSet = null;
+
+        dataCommunicator.refreshViewport();
+        fakeClientCommunication();
+        Assert.assertEquals(Range.withLength(0, 6), lastSet);
+    }
+
     @Test
     public void setFlushRequest_remove_setFlushRequest_reattach_noEndlessFlushLoop() {
         AtomicInteger listenerInvocationCounter = new AtomicInteger(0);

flow-data/src/test/java/com/vaadin/flow/data/provider/hierarchy/HierarchicalDataCommunicatorDataRefreshTest.java

@@ -2,6 +2,7 @@
 
 import java.util.Arrays;
 import java.util.Map;
+import java.util.concurrent.atomic.AtomicInteger;
 
 import org.junit.Assert;
 import org.junit.Before;
@@ -354,4 +355,30 @@ public void refreshAllItems_allItemsRemovedFromKeyMapper() {
         Assert.assertFalse(keyMapper.has(new Item("Item 0-0")));
         Assert.assertFalse(keyMapper.has(new Item("Item 0-0-0")));
     }
+
+    @Test
+    public void refreshViewport_updatedRangeSent() {
+        populateTreeData(treeData, 6, 1, 1);
+        dataCommunicator.expand(
+                Arrays.asList(new Item("Item 1"), new Item("Item 1-0")));
+        dataCommunicator.setViewportRange(0, 6);
+
+        var count = new AtomicInteger(0);
+        compositeDataGenerator.addDataGenerator(new DataGenerator<Item>() {
+            @Override
+            public void generateData(Item item, JsonObject json) {
+                json.put("count", String.valueOf(count.get()));
+            }
+        });
+
+        fakeClientCommunication();
+        assertArrayUpdateItems("count", "0", "0", "0", "0", "0", "0");
+
+        Mockito.clearInvocations(arrayUpdater, arrayUpdate);
+
+        count.incrementAndGet();
+        dataCommunicator.refreshViewport();
+        fakeClientCommunication();
+        assertArrayUpdateItems("count", "1", "1", "1", "1", "1", "1");
+    }
 }