feat: add virtual list item accessible name generator (#6977)

Author: tomivirkki

vaadin-virtual-list-flow-parent/vaadin-virtual-list-flow-integration-tests/src/main/java/com/vaadin/flow/component/virtuallist/tests/VirtualListPage.java

@@ -107,13 +107,21 @@ private void createListWithStrings() {
                 evt -> list.setItems("Another item 1", "Another item 2"));
         NativeButton setEmptyList = new NativeButton("Change list 3",
                 evt -> list.setItems());
+        NativeButton setItemAccessibleNameGenerator = new NativeButton(
+                "Set item accessible name generator",
+                evt -> list.setItemAccessibleNameGenerator(
+                        item -> item.contains("2") ? null
+                                : "Accessible " + item));
 
         list.setId("list-with-strings");
         setListWith3Items.setId("list-with-strings-3-items");
         setListWith2Items.setId("list-with-strings-2-items");
         setEmptyList.setId("list-with-strings-0-items");
+        setItemAccessibleNameGenerator
+                .setId("list-with-strings-accessible-name");
 
-        add(list, setListWith3Items, setListWith2Items, setEmptyList);
+        add(list, setListWith3Items, setListWith2Items, setEmptyList,
+                setItemAccessibleNameGenerator);
     }
 
     private void createDataProviderWithStrings() {

vaadin-virtual-list-flow-parent/vaadin-virtual-list-flow-integration-tests/src/test/java/com/vaadin/flow/component/virtuallist/tests/VirtualListIT.java

@@ -65,6 +65,27 @@ public void listWithStrings() {
         clickToSet0Items_listIsUpdated(listId, "list-with-strings-0-items");
     }
 
+    @Test
+    public void accessibleName() {
+        String listId = "list-with-strings";
+
+        var virtualList = $(VirtualListElement.class).id(listId);
+
+        var firstChildElement = virtualList
+                .findElement(By.xpath("//*[text()='Item 1']"));
+
+        Assert.assertFalse(firstChildElement.hasAttribute("aria-label"));
+
+        clickElementWithJs("list-with-strings-accessible-name");
+
+        Assert.assertEquals("Accessible Item 1",
+                firstChildElement.getAttribute("aria-label"));
+
+        var secondChildElement = virtualList
+                .findElement(By.xpath("//*[text()='Item 2']"));
+        Assert.assertFalse(secondChildElement.hasAttribute("aria-label"));
+    }
+
     @Test
     public void dataProviderWithStrings() {
         String listId = "dataprovider-with-strings";

vaadin-virtual-list-flow-parent/vaadin-virtual-list-flow/src/main/java/com/vaadin/flow/component/virtuallist/VirtualList.java

@@ -40,12 +40,14 @@
 import com.vaadin.flow.data.renderer.LitRenderer;
 import com.vaadin.flow.data.renderer.Renderer;
 import com.vaadin.flow.dom.DisabledUpdateMode;
+import com.vaadin.flow.function.SerializableFunction;
 import com.vaadin.flow.function.ValueProvider;
 import com.vaadin.flow.internal.JsonUtils;
 import com.vaadin.flow.server.Command;
 import com.vaadin.flow.shared.Registration;
 
 import elemental.json.Json;
+import elemental.json.JsonObject;
 import elemental.json.JsonValue;
 
 /**
@@ -119,6 +121,8 @@ public void initialize() {
 
     private Renderer<T> renderer;
 
+    private SerializableFunction<T, String> itemAccessibleNameGenerator = item -> null;
+
     private final CompositeDataGenerator<T> dataGenerator = new CompositeDataGenerator<>();
     private final List<Registration> renderingRegistrations = new ArrayList<>();
     private transient T placeholderItem;
@@ -134,6 +138,7 @@ public void initialize() {
     public VirtualList() {
         setRenderer((ValueProvider<T, String>) String::valueOf);
         addAttachListener((e) -> this.setPlaceholderItem(this.placeholderItem));
+        dataGenerator.addDataGenerator(this::generateItemAccessibleName);
     }
 
     private void initConnector() {
@@ -144,6 +149,13 @@ private void initConnector() {
                         getElement());
     }
 
+    private void generateItemAccessibleName(T item, JsonObject jsonObject) {
+        var accessibleName = this.itemAccessibleNameGenerator.apply(item);
+        if (accessibleName != null) {
+            jsonObject.put("accessibleName", accessibleName);
+        }
+    }
+
     @Override
     public void setDataProvider(DataProvider<T, ?> dataProvider) {
         Objects.requireNonNull(dataProvider, "The dataProvider cannot be null");
@@ -324,4 +336,32 @@ public void scrollToStart() {
     public void scrollToEnd() {
         scrollToIndex(Integer.MAX_VALUE);
     }
+
+    /**
+     * A function that generates accessible names for virtual list items. The
+     * function gets the item as an argument and the return value should be a
+     * string representing that item. The result gets applied to the
+     * corresponding virtual list child element as an `aria-label` attribute.
+     *
+     * @param itemAccessibleNameGenerator
+     *            the item accessible name generator to set, not {@code null}
+     * @throws NullPointerException
+     *             if {@code itemAccessibleNameGenerator} is {@code null}
+     */
+    public void setItemAccessibleNameGenerator(
+            SerializableFunction<T, String> itemAccessibleNameGenerator) {
+        Objects.requireNonNull(itemAccessibleNameGenerator,
+                "Item accessible name generator can not be null");
+        this.itemAccessibleNameGenerator = itemAccessibleNameGenerator;
+        getDataCommunicator().reset();
+    }
+
+    /**
+     * Gets the function that generates accessible names for virtual list items.
+     *
+     * @return the item accessible name generator
+     */
+    public SerializableFunction<T, String> getItemAccessibleNameGenerator() {
+        return itemAccessibleNameGenerator;
+    }
 }

vaadin-virtual-list-flow-parent/vaadin-virtual-list-flow/src/main/resources/META-INF/resources/frontend/virtualListConnector.js

@@ -15,6 +15,8 @@ window.Vaadin.Flow.virtualListConnector = {
     list.$connector = {};
     list.$connector.placeholderItem = { __placeholder: true };
 
+    list.itemAccessibleNameGenerator = (item) => item && item.accessibleName;
+
     const updateRequestedItem = function () {
       /*
        * TODO virtual list seems to do a small index adjustment after scrolling

vaadin-virtual-list-flow-parent/vaadin-virtual-list-flow/src/test/java/com/vaadin/flow/component/virtuallist/tests/VirtualListTest.java

@@ -21,6 +21,7 @@
 import org.junit.rules.ExpectedException;
 
 import com.vaadin.flow.component.virtuallist.VirtualList;
+import com.vaadin.flow.function.SerializableFunction;
 
 public class VirtualListTest {
 
@@ -49,4 +50,20 @@ public void paging_setPagingEnabled_throws() {
         exceptionRule.expectMessage("VirtualList does not support paging");
         virtualList.getDataCommunicator().setPagingEnabled(true);
     }
+
+    @Test
+    public void setItemAccessibleNameGenerator_get() {
+        VirtualList<String> virtualList = new VirtualList<>();
+        SerializableFunction<String, String> itemAccessibleNameGenerator = item -> "Accessible "
+                + item;
+        virtualList.setItemAccessibleNameGenerator(itemAccessibleNameGenerator);
+        Assert.assertEquals(itemAccessibleNameGenerator,
+                virtualList.getItemAccessibleNameGenerator());
+    }
+
+    @Test(expected = NullPointerException.class)
+    public void setItemAccessibleNameGenerator_nullThrows() {
+        VirtualList<String> virtualList = new VirtualList<>();
+        virtualList.setItemAccessibleNameGenerator(null);
+    }
 }