Adds isApplied feature for Binding

flow-data/src/main/java/com/vaadin/flow/data/binder/Binder.java

@@ -294,6 +294,44 @@ default BindingValidationStatus<TARGET> validate() {
          *         changes, otherwise {@literal false}.
          */
         boolean hasChanges();
+
+        /**
+         * Checks whether this binding should be processed during validation and
+         * writing to bean.
+         *
+         * @return {@literal true} if this binding should be processed,
+         *         {@literal false} if this binding should be ignored
+         */
+        default boolean isApplied() {
+            return getIsAppliedPredicate().test(this);
+        }
+
+        /**
+         * Gets predicate for testing {@link #isApplied()}. By default,
+         * non-visible components are ignored during validation and bean
+         * writing.
+         *
+         * @return predicate for testing {@link #isApplied()}
+         */
+        default SerializablePredicate<Binding<BEAN, TARGET>> getIsAppliedPredicate() {
+            return binding -> {
+                if (binding.getField() instanceof Component) {
+                    return ((Component) binding.getField()).isVisible();
+                } else {
+                    return true;
+                }
+            };
+        }
+
+        /**
+         * Sets a custom predicate for testing {@link #isApplied()}. Set to
+         * {@literal null} to restore default functionality.
+         *
+         * @param isAppliedPredicate
+         *            custom predicate for testing {@link #isApplied()}
+         */
+        void setIsAppliedPredicate(
+                SerializablePredicate<Binding<BEAN, TARGET>> isAppliedPredicate);
     }
 
     /**
@@ -1238,6 +1276,8 @@ protected static class BindingImpl<BEAN, FIELDVALUE, TARGET>
 
         private Registration onValidationStatusChange;
 
+        private SerializablePredicate<Binding<BEAN, TARGET>> isAppliedPredicate;
+
         public BindingImpl(BindingBuilderImpl<BEAN, FIELDVALUE, TARGET> builder,
                 ValueProvider<BEAN, TARGET> getter,
                 Setter<BEAN, TARGET> setter) {
@@ -1611,6 +1651,19 @@ public boolean hasChanges() throws IllegalStateException {
 
             return this.binder.hasChanges(this);
         }
+
+        @Override
+        public SerializablePredicate<Binding<BEAN, TARGET>> getIsAppliedPredicate() {
+            return isAppliedPredicate == null
+                    ? Binding.super.getIsAppliedPredicate()
+                    : isAppliedPredicate;
+        }
+
+        @Override
+        public void setIsAppliedPredicate(
+                SerializablePredicate<Binding<BEAN, TARGET>> isAppliedPredicate) {
+            this.isAppliedPredicate = isAppliedPredicate;
+        }
     }
 
     /**
@@ -2344,13 +2397,13 @@ private BinderValidationStatus<BEAN> doWriteIfValid(BEAN bean,
 
         // make a copy of the incoming bindings to avoid their modifications
         // during validation
-        Collection<Binding<BEAN, ?>> currentBindings = new ArrayList<>(
-                bindings);
+        Collection<Binding<BEAN, ?>> currentBindings = bindings.stream()
+                .filter(Binding::isApplied).collect(Collectors.toList());
 
         // First run fields level validation, if no validation errors then
         // update bean
         List<BindingValidationStatus<?>> bindingResults = currentBindings
-                .stream().map(b -> b.validate(false))
+                .stream().filter(Binding::isApplied).map(b -> b.validate(false))
                 .collect(Collectors.toList());
 
         if (bindingResults.stream()
@@ -2413,13 +2466,15 @@ private void doWriteDraft(BEAN bean, Collection<Binding<BEAN, ?>> bindings,
         Objects.requireNonNull(bean, "bean cannot be null");
 
         if (!forced) {
-            bindings.forEach(binding -> ((BindingImpl<BEAN, ?, ?>) binding)
-                    .writeFieldValue(bean));
+            bindings.stream().filter(Binding::isApplied)
+                    .forEach(binding -> ((BindingImpl<BEAN, ?, ?>) binding)
+                            .writeFieldValue(bean));
         } else {
             boolean isDisabled = isValidatorsDisabled();
             setValidatorsDisabled(true);
-            bindings.forEach(binding -> ((BindingImpl<BEAN, ?, ?>) binding)
-                    .writeFieldValue(bean));
+            bindings.stream().filter(Binding::isApplied)
+                    .forEach(binding -> ((BindingImpl<BEAN, ?, ?>) binding)
+                            .writeFieldValue(bean));
             setValidatorsDisabled(isDisabled);
         }
     }
@@ -2653,7 +2708,8 @@ public boolean isValid() {
      * @return an immutable list of validation results for bindings
      */
     private List<BindingValidationStatus<?>> validateBindings() {
-        return getBindings().stream().map(BindingImpl::doValidation)
+        return getBindings().stream().filter(Binding::isApplied)
+                .map(BindingImpl::doValidation)
                 .collect(Collectors.collectingAndThen(Collectors.toList(),
                         Collections::unmodifiableList));
     }

flow-data/src/test/java/com/vaadin/flow/data/binder/BinderTest.java

@@ -39,6 +39,7 @@
 import org.junit.Test;
 import org.junit.rules.ExpectedException;
 
+import com.vaadin.flow.component.Component;
 import com.vaadin.flow.component.HasValue;
 import com.vaadin.flow.component.UI;
 import com.vaadin.flow.data.binder.Binder.Binding;
@@ -754,6 +755,37 @@ public void withValidator_doesNotDisablesDefaulNullRepresentation() {
         Assert.assertEquals(newValue, item.getFirstName());
     }
 
+    @Test
+    public void withValidator_isAppliedIsEvaluated() {
+        // Binding has validator which always fails
+        Binding<Person, String> nameBinding = binder.forField(nameField)
+                .withValidator(name -> false, "")
+                .bind(Person::getFirstName, Person::setFirstName);
+        binder.setBean(item);
+
+        // Base state -> not valid
+        Assert.assertFalse(binder.isValid());
+
+        // Default -> non-visible field -> valid
+        ((Component) nameBinding.getField()).setVisible(false);
+        Assert.assertTrue(binder.isValid());
+
+        // isApplied = false -> valid
+        ((Component) nameBinding.getField()).setVisible(true);
+        nameBinding.setIsAppliedPredicate(p -> false);
+        Assert.assertTrue(binder.isValid());
+
+        // isApplied = true -> not valid
+        nameBinding.setIsAppliedPredicate(p -> true);
+        Assert.assertFalse(binder.isValid());
+
+        // Check removing predicate and restoring default behavior
+        nameBinding.setIsAppliedPredicate(null);
+        Assert.assertFalse(binder.isValid());
+        ((Component) nameBinding.getField()).setVisible(false);
+        Assert.assertTrue(binder.isValid());
+    }
+
     @Test
     public void setRequired_withErrorMessage_fieldGetsRequiredIndicatorAndValidator() {
         TestTextField textField = new TestTextField();