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feat: Add bindRequiredIndicatorVisible to HasValue / HasValueAndElement (#23589)
Allow all HasValueAndElement components to bind the required indicator visible state to a Signal, following the same pattern as bindReadOnly.
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‎flow-server/src/main/java/com/vaadin/flow/component/HasValue.java‎

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@@ -342,4 +342,38 @@ default void bindReadOnly(Signal<Boolean> readOnlySignal) {
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"Binding read only state to a Signal is not supported by "
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+ getClass().getSimpleName());
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}
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/**
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* Binds a {@link Signal}'s value to the required indicator visible state of
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* this component and keeps the state synchronized with the signal value
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* while the component is in attached state. When the component is in
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* detached state, signal value changes have no effect.
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* <p>
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* While a Signal is bound to the required indicator visible state, any
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* attempt to set the state manually with
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* {@link #setRequiredIndicatorVisible(boolean)} throws
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* {@link com.vaadin.flow.signals.BindingActiveException}. Same happens when
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* trying to bind a new Signal while one is already bound.
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* <p>
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* Example of usage:
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*
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* <pre>
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* ValueSignal&lt;Boolean&gt; signal = new ValueSignal&lt;&gt;(false);
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* Input component = new Input();
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* add(component);
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* component.bindRequiredIndicatorVisible(signal);
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* signal.set(true); // The required indicator becomes visible
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* </pre>
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*
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* @param requiredSignal
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* the signal to bind, not <code>null</code>
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* @throws com.vaadin.flow.signals.BindingActiveException
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* thrown when there is already an existing binding
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* @see #setRequiredIndicatorVisible(boolean)
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*/
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default void bindRequiredIndicatorVisible(Signal<Boolean> requiredSignal) {
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throw new UnsupportedOperationException(
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"Binding required indicator visible state to a Signal is not supported by "
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+ getClass().getSimpleName());
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}
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}

‎flow-server/src/main/java/com/vaadin/flow/component/HasValueAndElement.java‎

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@@ -55,4 +55,9 @@ default boolean isReadOnly() {
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default void bindReadOnly(Signal<Boolean> readOnlySignal) {
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getElement().bindProperty("readonly", readOnlySignal, null);
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}
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@Override
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default void bindRequiredIndicatorVisible(Signal<Boolean> requiredSignal) {
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getElement().bindProperty("required", requiredSignal, null);
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}
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}

‎flow-server/src/test/java/com/vaadin/flow/component/HasValueBindRequiredIndicatorVisibleTest.java‎

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/*
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* Copyright 2000-2026 Vaadin Ltd.
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*
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* Licensed under the Apache License, Version 2.0 (the "License"); you may not
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* use this file except in compliance with the License. You may obtain a copy of
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* the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations under
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* the License.
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*/
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package com.vaadin.flow.component;
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import org.junit.jupiter.api.Test;
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import com.vaadin.flow.dom.SignalsUnitTest;
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import com.vaadin.flow.signals.BindingActiveException;
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import com.vaadin.flow.signals.Signal;
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import com.vaadin.flow.signals.local.ValueSignal;
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import static org.junit.jupiter.api.Assertions.assertFalse;
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import static org.junit.jupiter.api.Assertions.assertThrows;
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import static org.junit.jupiter.api.Assertions.assertTrue;
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/**
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* Tests for {@link HasValue#bindRequiredIndicatorVisible(Signal)}.
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*/
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class HasValueBindRequiredIndicatorVisibleTest extends SignalsUnitTest {
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@Test
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public void bindRequired_elementAttachedBefore_bindingActive() {
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TestComponent component = new TestComponent();
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UI.getCurrent().add(component);
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assertFalse(component.isRequiredIndicatorVisible());
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ValueSignal<Boolean> signal = new ValueSignal<>(true);
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component.bindRequiredIndicatorVisible(signal);
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assertTrue(component.isRequiredIndicatorVisible());
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}
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@Test
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public void bindRequired_elementAttachedAfter_bindingActive() {
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TestComponent component = new TestComponent();
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assertFalse(component.isRequiredIndicatorVisible());
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ValueSignal<Boolean> signal = new ValueSignal<>(true);
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component.bindRequiredIndicatorVisible(signal);
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UI.getCurrent().add(component);
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assertTrue(component.isRequiredIndicatorVisible());
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}
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@Test
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public void bindRequired_elementAttached_bindingActive() {
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TestComponent component = new TestComponent();
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UI.getCurrent().add(component);
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ValueSignal<Boolean> signal = new ValueSignal<>(true);
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component.bindRequiredIndicatorVisible(signal);
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// initially true
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assertTrue(component.isRequiredIndicatorVisible());
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// true -> false
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signal.set(false);
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assertFalse(component.isRequiredIndicatorVisible());
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// false -> true
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signal.set(true);
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assertTrue(component.isRequiredIndicatorVisible());
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}
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@Test
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public void bindRequired_elementNotAttached_bindingInactive() {
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TestComponent component = new TestComponent();
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ValueSignal<Boolean> signal = new ValueSignal<>(true);
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component.bindRequiredIndicatorVisible(signal);
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signal.set(false);
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assertFalse(component.isRequiredIndicatorVisible());
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}
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@Test
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public void bindRequired_elementDetached_bindingInactive() {
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TestComponent component = new TestComponent();
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UI.getCurrent().add(component);
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ValueSignal<Boolean> signal = new ValueSignal<>(true);
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component.bindRequiredIndicatorVisible(signal);
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component.removeFromParent();
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signal.set(false); // ignored
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assertTrue(component.isRequiredIndicatorVisible());
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}
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@Test
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public void bindRequired_elementReAttached_bindingActivate() {
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TestComponent component = new TestComponent();
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UI.getCurrent().add(component);
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ValueSignal<Boolean> signal = new ValueSignal<>(true);
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component.bindRequiredIndicatorVisible(signal);
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component.removeFromParent();
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signal.set(false);
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UI.getCurrent().add(component);
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assertFalse(component.isRequiredIndicatorVisible());
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}
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@Test
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public void bindRequired_bindOrSetRequiredWhileBindingIsActive_throwException() {
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TestComponent component = new TestComponent();
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UI.getCurrent().add(component);
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component.bindRequiredIndicatorVisible(new ValueSignal<>(true));
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assertThrows(BindingActiveException.class, () -> component
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.bindRequiredIndicatorVisible(new ValueSignal<>(false)));
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assertThrows(BindingActiveException.class,
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() -> component.setRequiredIndicatorVisible(false));
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assertTrue(component.isRequiredIndicatorVisible());
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}
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@Test
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public void bindRequired_nullSignal_throwsNPE() {
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TestComponent component = new TestComponent();
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UI.getCurrent().add(component);
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assertThrows(NullPointerException.class,
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() -> component.bindRequiredIndicatorVisible(null));
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}
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@Test
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public void bindRequired_nullSignalValue_setsRequiredToFalse() {
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TestComponent component = new TestComponent();
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UI.getCurrent().add(component);
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ValueSignal<Boolean> signal = new ValueSignal<>(true);
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component.bindRequiredIndicatorVisible(signal);
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assertTrue(component.isRequiredIndicatorVisible());
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// null transforms to false (default value for boolean property)
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signal.set(null);
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assertFalse(component.isRequiredIndicatorVisible());
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}
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@Test
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public void bindRequired_toggleSignalValue_requiredUpdates() {
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TestComponent component = new TestComponent();
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UI.getCurrent().add(component);
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ValueSignal<Boolean> signal = new ValueSignal<>(false);
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component.bindRequiredIndicatorVisible(signal);
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assertFalse(component.isRequiredIndicatorVisible());
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signal.set(true);
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assertTrue(component.isRequiredIndicatorVisible());
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signal.set(false);
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assertFalse(component.isRequiredIndicatorVisible());
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signal.set(true);
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assertTrue(component.isRequiredIndicatorVisible());
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}
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/**
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* Test component implementing {@link HasValueAndElement}.
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*/
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@Tag(Tag.INPUT)
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private static class TestComponent
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extends AbstractField<TestComponent, String> {
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public TestComponent() {
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super("");
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}
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@Override
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protected void setPresentationValue(String newPresentationValue) {
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// NOP
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}
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}
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}

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