diff --git a/core/lib/Drupal/Core/Config/Schema/Mapping.php b/core/lib/Drupal/Core/Config/Schema/Mapping.php
index c09d9ad..e958f07 100644
--- a/core/lib/Drupal/Core/Config/Schema/Mapping.php
+++ b/core/lib/Drupal/Core/Config/Schema/Mapping.php
@@ -9,6 +9,7 @@
 
 use Drupal\Component\Utility\NestedArray;
 use Drupal\Core\TypedData\ComplexDataInterface;
+use Drupal\Core\TypedData\TypedDataInterface;
 use \InvalidArgumentException;
 
 /**
@@ -122,4 +123,14 @@ public function isEmpty() {
     return empty($this->value);
   }
 
+  /**
+   * Implements \Drupal\Core\TypedData\ComplexDataInterface::onChange().
+   */
+  public function onChange($property_name) {
+    // Notify the parent of changes.
+    if (isset($this->parent)) {
+      $this->parent->onChange($this->name);
+    }
+  }
+
 }
diff --git a/core/lib/Drupal/Core/Entity/Entity.php b/core/lib/Drupal/Core/Entity/Entity.php
index 49d2933..0b976c5 100644
--- a/core/lib/Drupal/Core/Entity/Entity.php
+++ b/core/lib/Drupal/Core/Entity/Entity.php
@@ -466,9 +466,9 @@ public function validate() {
   }
 
   /**
-   * Implements \Drupal\Core\TypedData\ComplexDataInterface::handleChanges().
+   * Implements \Drupal\Core\TypedData\ComplexDataInterface::onChange().
    */
-  public function handleChanges($property_name, TypedDataInterface $property, $new_value) {
+  public function onChange($property_name) {
     // Nothing to do.
   }
 
diff --git a/core/lib/Drupal/Core/Entity/EntityBCDecorator.php b/core/lib/Drupal/Core/Entity/EntityBCDecorator.php
index 3b8a069..497621e 100644
--- a/core/lib/Drupal/Core/Entity/EntityBCDecorator.php
+++ b/core/lib/Drupal/Core/Entity/EntityBCDecorator.php
@@ -513,7 +513,7 @@ public function getExportProperties() {
   /**
    * Forwards the call to the decorated entity.
    */
-  public function handleChanges($property_name, TypedDataInterface $property, $new_value) {
-    $this->decorated->handleChanges($property_name, $property, $new_value);
+  public function onChange($property_name) {
+    $this->decorated->onChange($property_name, $property, $new_value);
   }
 }
diff --git a/core/lib/Drupal/Core/Entity/Field/FieldItemBase.php b/core/lib/Drupal/Core/Entity/Field/FieldItemBase.php
index 701b461..ce1a98d 100644
--- a/core/lib/Drupal/Core/Entity/Field/FieldItemBase.php
+++ b/core/lib/Drupal/Core/Entity/Field/FieldItemBase.php
@@ -31,7 +31,7 @@ public function setValue($values, $notify = TRUE) {
     // Treat the values as property value of the first property, if no array is
     // given.
     if (!is_array($values)) {
-      $keys = array_keys($this->properties);
+      $keys = array_keys($this->getPropertyDefinitions());
       $values = array($keys[0] => $values);
     }
     parent::setValue($values, $notify);
@@ -52,11 +52,29 @@ public function __get($name) {
   }
 
   /**
+   * Overrides \Drupal\Core\TypedData\Type\Map::set().
+   */
+  public function set($property_name, $value) {
+    if (isset($this->properties[$property_name])) {
+      $this->properties[$property_name]->setValue($value);
+    }
+    else {
+      // Notify the parent of any changes to be made.
+      if (isset($this->parent)) {
+        $this->parent->onChange($this->name);
+      }
+      // Just set the plain value, which allows adding a new entry to the map.
+      $this->values[$property_name] = $value;
+    }
+  }
+
+  /**
    * Implements \Drupal\Core\Entity\Field\FieldItemInterface::__set().
    */
   public function __set($name, $value) {
-    // Support setting values via property objects.
-    if ($value instanceof TypedDataInterface) {
+    // Support setting values via property objects, but take care in as the
+    // value of the 'entity' property is typed data also.
+    if ($value instanceof TypedDataInterface && !($value instanceof \Drupal\Core\Entity\EntityInterface)) {
       $value = $value->getValue();
     }
     $this->set($name, $value);
@@ -66,7 +84,7 @@ public function __set($name, $value) {
    * Implements \Drupal\Core\Entity\Field\FieldItemInterface::__isset().
    */
   public function __isset($name) {
-    return isset($this->values[$name]) || isset($this->properties[$name]);
+    return isset($this->values[$name]) || (isset($this->properties[$name]) && $this->properties[$name]->getValue() !== NULL);
   }
 
   /**
@@ -77,12 +95,12 @@ public function __unset($name) {
   }
 
   /**
-   * Overrides \Drupal\Core\TypedData\Map::handleChanges().
+   * Overrides \Drupal\Core\TypedData\Map::onChange().
    */
-  public function handleChanges($property_name, TypedDataInterface $property, $new_value) {
+  public function onChange($property_name) {
     // Notify the parent of changes.
     if (isset($this->parent)) {
-      $this->parent->handleChanges($this->name, $property, $new_value);
+      $this->parent->onChange($this->name);
     }
     // Remove the plain value, such that any further __get() calls go via the
     // updated property object.
diff --git a/core/lib/Drupal/Core/Entity/Field/Type/EntityReferenceItem.php b/core/lib/Drupal/Core/Entity/Field/Type/EntityReferenceItem.php
index 330eb99..6971e39 100644
--- a/core/lib/Drupal/Core/Entity/Field/Type/EntityReferenceItem.php
+++ b/core/lib/Drupal/Core/Entity/Field/Type/EntityReferenceItem.php
@@ -8,6 +8,7 @@
 namespace Drupal\Core\Entity\Field\Type;
 
 use Drupal\Core\Entity\Field\FieldItemBase;
+use Drupal\Core\TypedData\TypedDataInterface;
 
 /**
  * Defines the 'entity_reference' entity field item.
@@ -69,37 +70,6 @@ public function getPropertyDefinitions() {
   }
 
   /**
-   * Overrides \Drupal\Core\Entity\Field\FieldItemBase::setValue().
-   */
-  public function setValue($values, $notify = TRUE) {
-    // Treat the values as property value of the entity field, if no array
-    // is given. That way we support setting the field by entity ID or object.
-    if (!is_array($values)) {
-      $values = array('entity' => $values);
-    }
-    // Notify the parent of any changes to be made.
-    if ($notify && isset($this->parent)) {
-      $this->parent->handleChanges($this->name, $this, $values);
-    }
-
-    // Entity is computed out of the ID, so we only need to update the ID. Only
-    // set the entity field if no ID is given.
-    if (isset($values['target_id'])) {
-      $this->properties['target_id']->setValue($values['target_id'], FALSE);
-    }
-    elseif (isset($values['entity'])) {
-      $this->properties['entity']->setValue($values['entity'], FALSE);
-    }
-    else {
-      $this->properties['entity']->setValue(NULL, FALSE);
-    }
-    unset($values['entity'], $values['target_id']);
-    if ($values) {
-      throw new \InvalidArgumentException('Property ' . key($values) . ' is unknown.');
-    }
-  }
-
-  /**
    * Overrides \Drupal\Core\Entity\Field\FieldItemBase::__get().
    */
   public function __get($name) {
@@ -116,22 +86,39 @@ public function get($property_name) {
   }
 
   /**
-   * Overrides \Drupal\Core\Entity\Field\FieldItemBase::__set().
-   */
-  public function __set($name, $value) {
-    // Support setting values via property objects, but take care in as the
-    // value of the 'entity' property is typed data also.
-    if ($value instanceof TypedDataInterface && !($value instanceof \Drupal\Core\Entity\EntityInterface)) {
-      $value = $value->getValue();
-    }
-    $this->set($name, $value);
-  }
-
-  /**
    * Implements \Drupal\Core\Entity\Field\FieldItemInterface::__isset().
    */
   public function __isset($property_name) {
     $property_name = ($property_name == 'value') ? 'target_id' : $property_name;
     return parent::__isset($property_name);
   }
+
+  /**
+   * Overrides \Drupal\Core\Entity\Field\FieldItemBase::get().
+   */
+  public function setValue($values, $notify = TRUE) {
+    // Treat the values as property value of the first property, if no array is
+    // given.
+    if (!is_array($values)) {
+      $keys = array_keys($this->getPropertyDefinitions());
+      $values = array($keys[0] => $values);
+    }
+
+    // Notify the parent of any changes to be made.
+    if ($notify && isset($this->parent)) {
+      $this->parent->onChange($this->name);
+    }
+    $this->values = $values;
+
+    // Update any existing property objects, except of 'entity'.
+    foreach ($this->properties as $name => $property) {
+      if ($name != 'entity') {
+        $value = NULL;
+        if (isset($values[$name])) {
+          $value = $values[$name];
+        }
+        $property->setValue($value, FALSE);
+      }
+    }
+  }
 }
diff --git a/core/lib/Drupal/Core/Entity/Field/Type/EntityTranslation.php b/core/lib/Drupal/Core/Entity/Field/Type/EntityTranslation.php
index 134e91d..4765a54 100644
--- a/core/lib/Drupal/Core/Entity/Field/Type/EntityTranslation.php
+++ b/core/lib/Drupal/Core/Entity/Field/Type/EntityTranslation.php
@@ -11,6 +11,7 @@
 use Drupal\Core\TypedData\ComplexDataInterface;
 use Drupal\Core\TypedData\TypedData;
 use ArrayIterator;
+use Drupal\Core\TypedData\TypedDataInterface;
 use IteratorAggregate;
 use InvalidArgumentException;
 
@@ -74,7 +75,7 @@ public function getValue() {
   public function setValue($values, $notify = TRUE) {
     // Notify the parent of any changes to be made.
     if ($notify && isset($this->parent)) {
-      $this->parent->handleChanges($this->name, $this, $values);
+      $this->parent->onChange($this->name);
     }
     $this->fields = $values;
   }
@@ -197,6 +198,16 @@ public function isEmpty() {
   }
 
   /**
+   * Implements \Drupal\Core\TypedData\ComplexDataInterface::onChange().
+   */
+  public function onChange($property_name) {
+    // Notify the parent of changes.
+    if (isset($this->parent)) {
+      $this->parent->onChange($this->name);
+    }
+  }
+
+  /**
    * Implements \Drupal\Core\TypedData\AccessibleInterface::access().
    */
   public function access($operation = 'view', \Drupal\user\Plugin\Core\Entity\User $account = NULL) {
diff --git a/core/lib/Drupal/Core/Entity/Field/Type/EntityWrapper.php b/core/lib/Drupal/Core/Entity/Field/Type/EntityWrapper.php
index 071ddb0..10492e6 100644
--- a/core/lib/Drupal/Core/Entity/Field/Type/EntityWrapper.php
+++ b/core/lib/Drupal/Core/Entity/Field/Type/EntityWrapper.php
@@ -8,7 +8,6 @@
 namespace Drupal\Core\Entity\Field\Type;
 
 use Drupal\Core\Entity\EntityInterface;
-use Drupal\Core\Entity\EntityNG;
 use Drupal\Core\TypedData\ComplexDataInterface;
 use Drupal\Core\TypedData\TypedData;
 use Drupal\Core\TypedData\TypedDataInterface;
@@ -74,18 +73,10 @@ public function getValue() {
     if (isset($this->newEntity)) {
       return $this->newEntity;
     }
-    $source = $this->getIdSource();
-    $id = $source ? $source->getValue() : $this->id;
-    return $id ? entity_load($this->entityType, $id) : NULL;
-  }
-
-  /**
-   * Helper to get the typed data object holding the source entity ID.
-   *
-   * @return \Drupal\Core\TypedData\TypedDataInterface|FALSE
-   */
-  protected function getIdSource() {
-    return !empty($this->definition['settings']['id source']) ? $this->parent->get($this->definition['settings']['id source']) : FALSE;
+    if (!empty($this->definition['settings']['id source'])) {
+      $this->id = $this->parent->__get($this->definition['settings']['id source']);
+    }
+    return $this->id ? entity_load($this->entityType, $this->id) : NULL;
   }
 
   /**
@@ -109,12 +100,15 @@ public function setValue($value, $notify = TRUE) {
     elseif (isset($value) && !(is_scalar($value) && !empty($this->definition['constraints']['EntityType']))) {
       throw new InvalidArgumentException('Value is not a valid entity.');
     }
-    // Now update the value in the source or the local id property.
-    $source = $this->getIdSource();
-    if ($source) {
-      $source->setValue($value);
+    // Update the 'id source' property, if given.
+    if (!empty($this->definition['settings']['id source'])) {
+      $this->parent->__set($this->definition['settings']['id source'], $value);
     }
     else {
+      // Notify the parent of any changes to be made.
+      if ($notify && isset($this->parent)) {
+        $this->parent->onChange($this->name);
+      }
       $this->id = $value;
     }
   }
@@ -214,12 +208,12 @@ public function isEmpty() {
   }
 
   /**
-   * Implements \Drupal\Core\TypedData\ComplexDataInterface::handleChanges().
+   * Implements \Drupal\Core\TypedData\ComplexDataInterface::onChange().
    */
-  public function handleChanges($property_name, TypedDataInterface $property, $new_value) {
+  public function onChange($property_name) {
     // Notify the parent of changes.
     if (isset($this->parent)) {
-      $this->parent->handleChanges($this->name, $property, $new_value);
+      $this->parent->onChange($this->name);
     }
   }
 }
diff --git a/core/lib/Drupal/Core/Entity/Field/Type/Field.php b/core/lib/Drupal/Core/Entity/Field/Type/Field.php
index b39e9a5..8c5451a 100644
--- a/core/lib/Drupal/Core/Entity/Field/Type/Field.php
+++ b/core/lib/Drupal/Core/Entity/Field/Type/Field.php
@@ -66,7 +66,11 @@ public function getValue() {
   /**
    * Overrides \Drupal\Core\TypedData\ItemList::setValue().
    */
-  public function setValue($values) {
+  public function setValue($values, $notify = TRUE) {
+    // Notify the parent of any changes to be made.
+    if ($notify && isset($this->parent)) {
+      $this->parent->onChange($this->name);
+    }
     if (!isset($values) || $values === array()) {
       $this->list = $values;
     }
@@ -114,7 +118,7 @@ public function getPropertyDefinitions() {
    * Implements \Drupal\Core\Entity\Field\FieldInterface::__get().
    */
   public function __get($property_name) {
-    return $this->offsetGet(0)->get($property_name)->getValue();
+    return $this->offsetGet(0)->__get($property_name);
   }
 
   /**
diff --git a/core/lib/Drupal/Core/Entity/Field/Type/LanguageItem.php b/core/lib/Drupal/Core/Entity/Field/Type/LanguageItem.php
index b3765b1..4f16384 100644
--- a/core/lib/Drupal/Core/Entity/Field/Type/LanguageItem.php
+++ b/core/lib/Drupal/Core/Entity/Field/Type/LanguageItem.php
@@ -8,7 +8,7 @@
 namespace Drupal\Core\Entity\Field\Type;
 
 use Drupal\Core\Entity\Field\FieldItemBase;
-use InvalidArgumentException;
+use Drupal\Core\TypedData\TypedDataInterface;
 
 /**
  * Defines the 'language_field' entity field item.
@@ -25,6 +25,16 @@ class LanguageItem extends FieldItemBase {
   static $propertyDefinitions;
 
   /**
+   * Overrides \Drupal\Core\TypedData\TypedData::__construct().
+   */
+  public function __construct(array $definition, $name = NULL, TypedDataInterface $parent = NULL) {
+    $this->definition = $definition;
+    $this->setContext($name, $parent);
+    // Initialize the language property by default.
+    $this->properties['language'] = typed_data()->getPropertyInstance($this, 'language');
+  }
+
+  /**
    * Implements \Drupal\Core\TypedData\ComplexDataInterface::getPropertyDefinitions().
    */
   public function getPropertyDefinitions() {
@@ -47,30 +57,31 @@ public function getPropertyDefinitions() {
   }
 
   /**
-   * Overrides FieldItemBase::setValue().
+   * Overrides \Drupal\Core\Entity\Field\FieldItemBase::get().
    */
-  public function setValue($values) {
-    // Treat the values as property value of the object property, if no array
-    // is given. That way we support setting the field by language code or
-    // object.
+  public function setValue($values, $notify = TRUE) {
+    // Treat the values as property value of the first property, if no array is
+    // given.
     if (!is_array($values)) {
-      $values = array('language' => $values);
+      $keys = array_keys($this->getPropertyDefinitions());
+      $values = array($keys[0] => $values);
     }
 
-    // Language is computed out of the langcode, so we only need to update the
-    // langcode. Only set the language property if no langcode is given.
-    if (!empty($values['value'])) {
-      $this->properties['value']->setValue($values['value']);
+    // Notify the parent of any changes to be made.
+    if ($notify && isset($this->parent)) {
+      $this->parent->onChange($this->name);
     }
-    elseif (isset($values['language'])) {
-      $this->properties['language']->setValue($values['language']);
-    }
-    else {
-      $this->properties['language']->setValue(NULL);
-    }
-    unset($values['language'], $values['value']);
-    if ($values) {
-      throw new InvalidArgumentException('Property ' . key($values) . ' is unknown.');
+    $this->values = $values;
+
+    // Update any existing property objects, except of 'entity'.
+    foreach ($this->properties as $name => $property) {
+      if ($name != 'language') {
+        $value = NULL;
+        if (isset($values[$name])) {
+          $value = $values[$name];
+        }
+        $property->setValue($value, FALSE);
+      }
     }
   }
 }
diff --git a/core/lib/Drupal/Core/TypedData/ComplexDataInterface.php b/core/lib/Drupal/Core/TypedData/ComplexDataInterface.php
index 132212a..e3a540b 100644
--- a/core/lib/Drupal/Core/TypedData/ComplexDataInterface.php
+++ b/core/lib/Drupal/Core/TypedData/ComplexDataInterface.php
@@ -122,19 +122,12 @@ public function getPropertyDefinitions();
   public function isEmpty();
 
   /**
-   * Handle changes to a child property or item, if any.
+   * React to changes to a child property.
    *
-   * For example, if the 'value' property of a child 'body' property is changed
-   * the body property would be passed along with property path 'body.value'.
+   * Note that this is invoked before any changes are applied.
    *
    * @param $property_name
-   *   The name of the property which has been changed.
-   * @param \Drupal\Core\TypedData\TypedDataInterface $changed
-   *   The typed data object being the source of the changes. This might be the
-   *   direct child property notifying the parent of changes, or any other
-   *   descendent item.
-   * @param mixed $new_value
-   *   The new value being set on the changed object.
+   *   The name of the property which is changed.
    */
-  public function handleChanges($property_name, TypedDataInterface $changed, $new_value);
+  public function onChange($property_name);
 }
diff --git a/core/lib/Drupal/Core/TypedData/ItemList.php b/core/lib/Drupal/Core/TypedData/ItemList.php
index 24a7d72..88af366 100644
--- a/core/lib/Drupal/Core/TypedData/ItemList.php
+++ b/core/lib/Drupal/Core/TypedData/ItemList.php
@@ -41,7 +41,11 @@ public function getValue() {
    * @param array|null $values
    *   An array of values of the field items, or NULL to unset the field.
    */
-  public function setValue($values) {
+  public function setValue($values, $notify = TRUE) {
+    // Notify the parent of any changes to be made.
+    if ($notify && isset($this->parent)) {
+      $this->parent->onChange($this->name);
+    }
     if (!isset($values) || $values === array()) {
       $this->list = $values;
     }
@@ -197,6 +201,16 @@ public function isEmpty() {
   }
 
   /**
+   * Implements \Drupal\Core\TypedData\ListInterface::onChange().
+   */
+  public function onChange($delta) {
+    // Notify the parent of changes.
+    if (isset($this->parent)) {
+      $this->parent->onChange($this->name);
+    }
+  }
+
+  /**
    * Magic method: Implements a deep clone.
    */
   public function __clone() {
diff --git a/core/lib/Drupal/Core/TypedData/ListInterface.php b/core/lib/Drupal/Core/TypedData/ListInterface.php
index 5bca254..2711cd4 100644
--- a/core/lib/Drupal/Core/TypedData/ListInterface.php
+++ b/core/lib/Drupal/Core/TypedData/ListInterface.php
@@ -20,7 +20,7 @@
  * When implementing this interface which extends Traversable, make sure to list
  * IteratorAggregate or Iterator before this interface in the implements clause.
  */
-interface ListInterface extends ArrayAccess, Countable, Traversable, TypedDataInterface {
+interface ListInterface extends TypedDataInterface, ArrayAccess, Countable, Traversable {
 
   /**
    * Determines whether the list contains any non-empty items.
@@ -37,4 +37,14 @@ public function isEmpty();
    *   The data definition of contained items.
    */
   public function getItemDefinition();
+
+  /**
+   * React to changes to a child item.
+   *
+   * Note that this is invoked before any changes are applied.
+   *
+   * @param $delta
+   *   The delta of the item which is changed.
+   */
+  public function onChange($delta);
 }
diff --git a/core/lib/Drupal/Core/TypedData/Type/Binary.php b/core/lib/Drupal/Core/TypedData/Type/Binary.php
index 3e4c312..f9c4985 100644
--- a/core/lib/Drupal/Core/TypedData/Type/Binary.php
+++ b/core/lib/Drupal/Core/TypedData/Type/Binary.php
@@ -53,7 +53,7 @@ public function getValue() {
   public function setValue($value, $notify = TRUE) {
     // Notify the parent of any changes to be made.
     if ($notify && isset($this->parent)) {
-      $this->parent->handleChanges($this->name, $this, $value);
+      $this->parent->onChange($this->name);
     }
     if (!isset($value)) {
       $this->handle = NULL;
diff --git a/core/lib/Drupal/Core/TypedData/Type/Date.php b/core/lib/Drupal/Core/TypedData/Type/Date.php
index dcf661a..c9b8c6b 100644
--- a/core/lib/Drupal/Core/TypedData/Type/Date.php
+++ b/core/lib/Drupal/Core/TypedData/Type/Date.php
@@ -34,7 +34,7 @@ class Date extends TypedData {
   public function setValue($value, $notify = TRUE) {
     // Notify the parent of any changes to be made.
     if ($notify && isset($this->parent)) {
-      $this->parent->handleChanges($this->name, $this, $value);
+      $this->parent->onChange($this->name);
     }
     // Don't try to create a date from an empty value.
     // It would default to the current time.
diff --git a/core/lib/Drupal/Core/TypedData/Type/Duration.php b/core/lib/Drupal/Core/TypedData/Type/Duration.php
index f91fcb9..52ba97d 100644
--- a/core/lib/Drupal/Core/TypedData/Type/Duration.php
+++ b/core/lib/Drupal/Core/TypedData/Type/Duration.php
@@ -34,7 +34,7 @@ class Duration extends TypedData {
   public function setValue($value, $notify = TRUE) {
     // Notify the parent of any changes to be made.
     if ($notify && isset($this->parent)) {
-      $this->parent->handleChanges($this->name, $this, $value);
+      $this->parent->onChange($this->name);
     }
     // Catch any exceptions thrown due to invalid values being passed.
     try {
diff --git a/core/lib/Drupal/Core/TypedData/Type/Language.php b/core/lib/Drupal/Core/TypedData/Type/Language.php
index c16fbc4..0127314 100644
--- a/core/lib/Drupal/Core/TypedData/Type/Language.php
+++ b/core/lib/Drupal/Core/TypedData/Type/Language.php
@@ -38,33 +38,21 @@ class Language extends TypedData {
    * Overrides TypedData::getValue().
    */
   public function getValue() {
-    $source = $this->getLanguageCodeSource();
-    $langcode = $source ? $source->getValue() : $this->langcode;
-    if ($langcode) {
-      $language = language_load($langcode);
+    if (!empty($this->definition['settings']['langcode source'])) {
+      $this->langcode = $this->parent->__get($this->definition['settings']['langcode source']);
+    }
+   if ($this->langcode) {
+      $language = language_load($this->langcode);
       return $language ?: new LanguageObject(array('langcode' => $this->langcode));
     }
   }
 
   /**
-   * Helper to get the typed data object holding the source language code.
-   *
-   * @return \Drupal\Core\TypedData\TypedDataInterface|FALSE
-   */
-  protected function getLanguageCodeSource() {
-    return !empty($this->definition['settings']['langcode source']) ? $this->parent->get($this->definition['settings']['langcode source']) : FALSE;
-  }
-
-  /**
    * Overrides TypedData::setValue().
    *
    * Both the langcode and the language object may be passed as value.
    */
   public function setValue($value, $notify = TRUE) {
-    // Notify the parent of any changes to be made.
-    if ($notify && isset($this->parent)) {
-      $this->parent->handleChanges($this->name, $this, $value);
-    }
     // Support passing language objects.
     if (is_object($value)) {
       $value = $value->langcode;
@@ -72,12 +60,15 @@ public function setValue($value, $notify = TRUE) {
     elseif (isset($value) && !is_scalar($value)) {
       throw new InvalidArgumentException('Value is no valid langcode or language object.');
     }
-    // Now update the value in the source or the local langcode property.
-    $source = $this->getLanguageCodeSource();
-    if ($source) {
-      $source->setValue($value);
+    // Update the 'langcode source' property, if given.
+    if (!empty($this->definition['settings']['langcode source'])) {
+      $this->parent->__set($this->definition['settings']['langcode source'], $value);
     }
     else {
+      // Notify the parent of any changes to be made.
+      if ($notify && isset($this->parent)) {
+        $this->parent->onChange($this->name);
+      }
       $this->langcode = $value;
     }
   }
diff --git a/core/lib/Drupal/Core/TypedData/Type/Map.php b/core/lib/Drupal/Core/TypedData/Type/Map.php
index 2464c23..a05497d 100644
--- a/core/lib/Drupal/Core/TypedData/Type/Map.php
+++ b/core/lib/Drupal/Core/TypedData/Type/Map.php
@@ -58,7 +58,13 @@ public function getValue() {
     foreach ($this->properties as $name => $property) {
       $definition = $property->getDefinition();
       if (empty($definition['computed'])) {
-        $this->values[$name] = $property->getValue();
+        $value = $property->getValue();
+        if (isset($value)) {
+          $this->values[$name] = $property->getValue();
+        }
+        else {
+          unset($this->values[$name]);
+        }
       }
     }
     return $this->values;
@@ -76,20 +82,17 @@ public function setValue($values, $notify = TRUE) {
     }
     // Notify the parent of any changes to be made.
     if ($notify && isset($this->parent)) {
-      $this->parent->handleChanges($this->name, $this, $value);
+      $this->parent->onChange($this->name);
     }
     $this->values = $values;
 
     // Update any existing property objects.
     foreach ($this->properties as $name => $property) {
-      $definition = $property->getDefinition();
-      if (empty($definition['computed'])) {
-        $value = NULL;
-        if (isset($values[$name])) {
-          $value = $values[$name];
-        }
-        $property->setValue($value, FALSE);
+      $value = NULL;
+      if (isset($values[$name])) {
+        $value = $values[$name];
       }
+      $property->setValue($value, FALSE);
     }
   }
 
@@ -110,8 +113,12 @@ public function getString() {
    */
   public function get($property_name) {
     if (!isset($this->properties[$property_name])) {
+      $value = NULL;
+      if (isset($this->values[$property_name])) {
+        $value = $this->values[$property_name];
+      }
       // If the property is unknown, this will throw an exception.
-      $this->properties[$property_name] = typed_data()->getPropertyInstance($this, $property_name);
+      $this->properties[$property_name] = typed_data()->getPropertyInstance($this, $property_name, $value);
     }
     return $this->properties[$property_name];
   }
@@ -198,19 +205,19 @@ public function isEmpty() {
    * Magic method: Implements a deep clone.
    */
   public function __clone() {
-    foreach ($this->getProperties() as $name => $property) {
+    foreach ($this->properties as $name => $property) {
       $this->properties[$name] = clone $property;
       $this->properties[$name]->setContext($name, $this);
     }
   }
 
   /**
-   * Implements \Drupal\Core\TypedData\ComplexDataInterface::handleChanges().
+   * Implements \Drupal\Core\TypedData\ComplexDataInterface::onChange().
    */
-  public function handleChanges($property_name, TypedDataInterface $property, $new_value) {
+  public function onChange($property_name) {
     // Notify the parent of changes.
     if (isset($this->parent)) {
-      $this->parent->handleChanges($this->name, $property, $new_value);
+      $this->parent->onChange($this->name);
     }
   }
 }
diff --git a/core/lib/Drupal/Core/TypedData/TypedData.php b/core/lib/Drupal/Core/TypedData/TypedData.php
index 1ea98c2..e9558f3 100644
--- a/core/lib/Drupal/Core/TypedData/TypedData.php
+++ b/core/lib/Drupal/Core/TypedData/TypedData.php
@@ -52,7 +52,8 @@
    */
   public function __construct(array $definition, $name = NULL, TypedDataInterface $parent = NULL) {
     $this->definition = $definition;
-    $this->setContext($name, $parent);
+    $this->parent = $parent;
+    $this->name = $name;
   }
 
   /**
@@ -82,7 +83,7 @@ public function getValue() {
   public function setValue($value, $notify = TRUE) {
     // Notify the parent of any changes to be made.
     if ($notify && isset($this->parent)) {
-      $this->parent->handleChanges($this->name, $this, $value);
+      $this->parent->onChange($this->name);
     }
     $this->value = $value;
   }
diff --git a/core/lib/Drupal/Core/TypedData/TypedDataManager.php b/core/lib/Drupal/Core/TypedData/TypedDataManager.php
index 098be1f..195e32d 100644
--- a/core/lib/Drupal/Core/TypedData/TypedDataManager.php
+++ b/core/lib/Drupal/Core/TypedData/TypedDataManager.php
@@ -145,7 +145,7 @@ public function createInstance($plugin_id, array $configuration, $name = NULL, $
   public function create(array $definition, $value = NULL, $name = NULL, $parent = NULL) {
     $wrapper = $this->factory->createInstance($definition['type'], $definition, $name, $parent);
     if (isset($value)) {
-      $wrapper->setValue($value);
+      $wrapper->setValue($value, FALSE);
     }
     return $wrapper;
   }
@@ -249,7 +249,7 @@ public function getPropertyInstance($object, $property_name, $value = NULL) {
     $property = clone $this->prototypes[$key];
     $property->setContext($property_name, $object);
     if (isset($value)) {
-      $property->setValue($value);
+      $property->setValue($value, FALSE);
     }
     return $property;
   }
diff --git a/core/modules/file/lib/Drupal/file/Type/FileItem.php b/core/modules/file/lib/Drupal/file/Type/FileItem.php
index e1c7d24..a4dd7e5 100644
--- a/core/modules/file/lib/Drupal/file/Type/FileItem.php
+++ b/core/modules/file/lib/Drupal/file/Type/FileItem.php
@@ -8,6 +8,7 @@
 namespace Drupal\file\Type;
 
 use Drupal\Core\Entity\Field\FieldItemBase;
+use Drupal\Core\TypedData\TypedDataInterface;
 
 /**
  * Defines the 'file_field' entity field item.
@@ -24,6 +25,16 @@ class FileItem extends FieldItemBase {
   static $propertyDefinitions;
 
   /**
+   * Overrides \Drupal\Core\TypedData\TypedData::__construct().
+   */
+  public function __construct(array $definition, $name = NULL, TypedDataInterface $parent = NULL) {
+    $this->definition = $definition;
+    $this->setContext($name, $parent);
+    // Initialize the entity property by default.
+    $this->properties['entity'] = typed_data()->getPropertyInstance($this, 'entity');
+  }
+
+  /**
    * Implements \Drupal\Core\TypedData\ComplexDataInterface::getPropertyDefinitions().
    */
   public function getPropertyDefinitions() {
@@ -57,37 +68,31 @@ public function getPropertyDefinitions() {
   }
 
   /**
-   * Overrides \Drupal\Core\Entity\Field\FieldItemBase::setValue().
+   * Overrides \Drupal\Core\Entity\Field\FieldItemBase::get().
    */
-  public function setValue($values) {
-    // Treat the values as property value of the entity field, if no array
-    // is given.
+  public function setValue($values, $notify = TRUE) {
+    // Treat the values as property value of the first property, if no array is
+    // given.
     if (!is_array($values)) {
-      $values = array('entity' => $values);
+      $keys = array_keys($this->getPropertyDefinitions());
+      $values = array($keys[0] => $values);
     }
 
-    if (isset($values['display'])) {
-      $this->properties['display']->setValue($values['display']);
-    }
-    if (isset($values['description'])) {
-      $this->properties['description']->setValue($values['description']);
+    // Notify the parent of any changes to be made.
+    if ($notify && isset($this->parent)) {
+      $this->parent->onChange($this->name);
     }
+    $this->values = $values;
 
-    // Entity is computed out of the ID, so we only need to update the ID. Only
-    // set the entity field if no ID is given.
-    if (isset($values['fid'])) {
-      $this->properties['fid']->setValue($values['fid']);
-    }
-    elseif (isset($values['entity'])) {
-      $this->properties['entity']->setValue($values['entity']);
-    }
-    else {
-      $this->properties['entity']->setValue(NULL);
-    }
-    unset($values['entity'], $values['fid'], $values['display'], $values['description']);
-    if ($values) {
-      throw new \InvalidArgumentException('Property ' . key($values) . ' is unknown.');
+    // Update any existing property objects, except of 'entity'.
+    foreach ($this->properties as $name => $property) {
+      if ($name != 'entity') {
+        $value = NULL;
+        if (isset($values[$name])) {
+          $value = $values[$name];
+        }
+        $property->setValue($value, FALSE);
+      }
     }
   }
-
 }
diff --git a/core/modules/taxonomy/lib/Drupal/taxonomy/Type/TaxonomyTermReferenceItem.php b/core/modules/taxonomy/lib/Drupal/taxonomy/Type/TaxonomyTermReferenceItem.php
index 7f7ab02..4029e90 100644
--- a/core/modules/taxonomy/lib/Drupal/taxonomy/Type/TaxonomyTermReferenceItem.php
+++ b/core/modules/taxonomy/lib/Drupal/taxonomy/Type/TaxonomyTermReferenceItem.php
@@ -8,6 +8,7 @@
 namespace Drupal\taxonomy\Type;
 
 use Drupal\Core\Entity\Field\FieldItemBase;
+use Drupal\Core\TypedData\TypedDataInterface;
 
 /**
  * Defines the 'taxonomy_term_reference' entity field item.
@@ -24,6 +25,16 @@ class TaxonomyTermReferenceItem extends FieldItemBase {
   static $propertyDefinitions;
 
   /**
+   * Overrides \Drupal\Core\TypedData\TypedData::__construct().
+   */
+  public function __construct(array $definition, $name = NULL, TypedDataInterface $parent = NULL) {
+    $this->definition = $definition;
+    $this->setContext($name, $parent);
+    // Initialize the entity property by default.
+    $this->properties['entity'] = typed_data()->getPropertyInstance($this, 'entity');
+  }
+
+  /**
    * Implements \Drupal\Core\TypedData\ComplexDataInterface::getPropertyDefinitions().
    */
   public function getPropertyDefinitions() {
@@ -49,30 +60,31 @@ public function getPropertyDefinitions() {
   }
 
   /**
-   * Overrides \Drupal\Core\Entity\Field\FieldItemBase::setValue().
+   * Overrides \Drupal\Core\Entity\Field\FieldItemBase::get().
    */
-  public function setValue($values) {
-    // Treat the values as property value of the entity field, if no array
-    // is given.
+  public function setValue($values, $notify = TRUE) {
+    // Treat the values as property value of the first property, if no array is
+    // given.
     if (!is_array($values)) {
-      $values = array('entity' => $values);
+      $keys = array_keys($this->getPropertyDefinitions());
+      $values = array($keys[0] => $values);
     }
 
-    // Entity is computed out of the ID, so we only need to update the ID. Only
-    // set the entity field if no ID is given.
-    if (isset($values['tid'])) {
-      $this->properties['tid']->setValue($values['tid']);
+    // Notify the parent of any changes to be made.
+    if ($notify && isset($this->parent)) {
+      $this->parent->onChange($this->name);
     }
-    elseif (isset($values['entity'])) {
-      $this->properties['entity']->setValue($values['entity']);
-    }
-    else {
-      $this->properties['entity']->setValue(NULL);
-    }
-    unset($values['entity'], $values['tid']);
-    if ($values) {
-      throw new \InvalidArgumentException('Property ' . key($values) . ' is unknown.');
+    $this->values = $values;
+
+    // Update any existing property objects, except of 'entity'.
+    foreach ($this->properties as $name => $property) {
+      if ($name != 'entity') {
+        $value = NULL;
+        if (isset($values[$name])) {
+          $value = $values[$name];
+        }
+        $property->setValue($value, FALSE);
+      }
     }
   }
-
 }
diff --git a/core/modules/views/views_ui/lib/Drupal/views_ui/ViewUI.php b/core/modules/views/views_ui/lib/Drupal/views_ui/ViewUI.php
index 83abb4b..9114a6a 100644
--- a/core/modules/views/views_ui/lib/Drupal/views_ui/ViewUI.php
+++ b/core/modules/views/views_ui/lib/Drupal/views_ui/ViewUI.php
@@ -1069,9 +1069,9 @@ public function setContext($name = NULL, TypedDataInterface $parent = NULL) {
   }
 
   /**
-   * Implements \Drupal\Core\TypedData\TypedDataInterface::handleChanges().
+   * Implements \Drupal\Core\TypedData\TypedDataInterface::onChange().
    */
-  public function handleChanges($property_name, TypedDataInterface $property, $new_value) {
+  public function onChange($property_name) {
     return $this->__call(__FUNCTION__, func_get_args());
   }
 }