Note to non-wiki readers: This documentation is generated from the GEF@github.com wiki - if you have corrections or additions it would be awesome if you could contribute them to the original wiki page .

## Introduction

The Common component provides key concepts and infrastructure to be potentially used by all other GEF components. It is internally comprised out of a single Common module.

## Common

- feature: org.eclipse.gef.common
- bundle: org.eclipse.gef.common

The Common module of Common provides basic abstractions and related support classes within the following packages:

- Activate: A general abstraction for activatable objects and a related support class
- Adapt: A general abstraction for adaptable objects and related support classes
- Adapt.Inject: Google Guice-based support for injecting and scoping adapters at adaptable objects
- Attributes: A general abstraction of an attribute store
- Beans.Binding: JavaFX-style bindings for the properties provided by Beans.Property.
- Beans.Property: JavaFX-style properties for Google Guava's com.google.common.collect.Multiset and com.google.common.collect.SetMultimap as well as replacements for JavaFX's Set, List, and Map collection properties
- Beans.Value: Observable value abstraction related to the collections offered by Collections as well as writable value abstractions related to the properties offered by Beans.Property.
- Collections: JavaFX-style observable collections for Google Guava's com.google.common.collect.Multiset and com.google.common.collect.SetMultimap collections and related listener abstractions.
- Dispose: A general abstraction for disposable objects
- Reflect: A utility class for working with Java Reflection

### Activate

- package: org.eclipse.gef.common.activate

The Activate package provides a general abstraction for objects that maintain an active state ( IActivatable) as well as a support-class ( ActivatableSupport) that can be used as a delegate to simply implement IActivatable conferment to its contract.

#### IActivatable

An `IActivatable` maintains an 'active' state and can be activated and deactivated. The active state of an `IActivatable` is exposed via an (observable) javafx.beans.property.ReadOnlyBooleanProperty, so listeners can easily observe the active state.

#### ActivatableSupport

To enforce that implementers of IActivatable properly follow the above outlined contract, `ActivatableSupport` may be used. It does not formally implement the IActivatable interface but provides implementations for all its methods and can thus be simply used as a delegate, as follows:

    public class MyActivatable implements IActivatable {

      // create delegate
      private ActivatableSupport acs = new ActivatableSupport(this);

      public void activate() {
        acs.activate(null /* pre-activation hook */, this::doActivate /* post-activation hook */);
      }

      ...
    }

### Adapt

- package: org.eclipse.gef.common.adapt

The Adapt package provides a modernized interpretation of org.eclipse.core.runtime.IAdaptable. The motivation behind this extension and a short overview is given in IAdaptable - GEF's Interpretation of a Classic. In detail, the enhancements provided by Adapt are:

1. Adapters may be registered and retrieved by means of a com.google.common.reflect.TypeToken key as an alternative to a Class key, which ensures that adapters with parameterized types may also be registered and retrieved in a type-safe manner, not only via their raw type. For instance, an adapter instance a1 of parameterized type A<T1> and an instance a2 of type A<T2> can both be registered at an IAdaptable. The MVC component makes use of this intensively, when registering providers, i.e. a Provider<? extends IGeometry> and a Provider<? extends IFXAnchor> can both be registered at an IVisualPart simultaneously.
2. Adapters may (optionally) be registered and retrieved by providing an additional role key, which allows to register multiple adapters of the same type (using different roles) at an IAdaptable. For instance, adapter instances a1 and a2 of type A can both be registered at an adaptable using different roles. The MVC component again makes use of this, when registering providers. Different geometry providers (Provider<? extends IGeometry>) are e.g. registered for selection and hover feedback, by registering respective providers with respective roles.
3. Adapters may request a back-reference to the respective IAdaptable they get registered at, by implementing a respective back-interface ( IAdaptable.Bound). Again, this is intensively used within MVC, where an IBehavior or IPolicy for instance needs to be aware of the host IVisualPart it is registered at.
4. IAdaptable provides support for registering property change listeners, to be notified whenever adapters are registered or unregistered.

Besides the IAdaptable, IAdaptable.Bound, and AdapterKey abstractions that formalize the modernized adaptable pattern, the package also provides a supporting class ( AdaptableSupport) to implement IAdaptable in compliance with its contract, as well as a standalone implementation ( AdapterStore).

#### IAdaptable, AdapterKey

An `IAdaptable` provides facilities to register adapters and to retrieve them via a combination of a type key ( java.lang.Class or com.google.common.reflect.TypeToken) and an (optional) java.lang.String role, which are combined in an `AdapterKey`. Having the option to use a com.google.common.reflect.TypeToken instead of a simple java.lang.Class key, enables the type-safe retrieval of adapters with parameterized types. The combination with an additional (optional) role enables that multiple adapters of the same type may be registered at an `IAdaptable`.

The 'traditional' getAdapter(Class<T>) method provided by the Eclipse Core Runtime org.eclipse.core.runtime.IAdaptable here is a mere convenience operation that will retrieve the single adapter registered with the respective java.lang.Class key and the default role (or the only adapter registered under the given java.lang.Class key, if there is only one adapter for that type key).

Before retrieving adapters from an `IAdaptable`, they have to be registered. The registration again includes a role (while a 'default' role is used in case no role is provided) and might require additional information about the actual adapter type by means of a com.google.common.reflect.TypeToken. The additional type information is required in case it cannot be inferred from the registered adapter instance itself (which is the case for parameterized types).

An adapter can thus now be registered and retrieved in various ways:

      // register and retrieve adapter 'a' of raw type 'A' under 'default' role (type info not required)
      adaptable.setAdapter(a);
      A a = adaptable.getAdapter(A.class);

      // register and retrieve adapter 'a' of parameterized type 'A<T>' under 'default' role (type info required)
      adaptable.setAdapter(new TypeToken<A<T>>(){}, a);
      A<T> a = adaptable.getAdapter(new TypeToken<A<T>>(){});

      // register and retrieve adapter 'a' of raw type 'A' under role 'a1' (type info not required)
      adaptable.setAdapter(a, "a1");
      A a = adaptable.getAdapter(AdapterKey.get(A.class, "a1"));

      // register and retrieve adapter 'a' of parameterized type 'A<T>' under role 'a1' (type info required)
      adaptable.setAdapter(new TypeToken<A<T>>(){}, a, "a1");
      A a = adaptable.getAdapter(AdapterKey.get(new TypeToken<A<T>>(){}, "a1"));

To formalize support for notifying listeners about registration and unregistration of adapters, `IAdaptable` provides its adapters via an javafx.collections.ObservableMap and an (unmodifiable) javafx.beans.property.ReadOnlyMapProperty.

#### IAdaptable.Bound

To formalize that an adapter may need to obtain a back reference to an IAdaptable, the `IAdaptable.Bound` interface was introduced. If an adapter implements this interface, the adaptable at which the adapter is registered is responsible of providing a back reference to the adapter as follows:

    public class MyAdaptable implements IAdaptable {

      public <T> void setAdapter(T adapter) {
        ...
        if (adapter instanceof IAdaptable.Bound) {
          ((IAdaptable.Bound<A>) adapter).setAdaptable(this);
        ...
      }

      public <T> void unsetAdapter(T adapter) {
        ...
        if (adapter instanceof IAdaptable.Bound) {
          ((IAdaptable.Bound<A>) adapter).setAdaptable(null);
        }
        ...
      }

      ...
    }

#### AdaptableSupport

To enforce that implementers of IAdaptable properly follow the above outlined contract, `AdaptableSupport` may be used. It does not formally implement the IAdaptable interface but provides implementations for all its methods and can thus be simply used as a delegate, as follows:

    public class MyAdaptable implements IAdaptable {

      // create delegate
      private AdaptableSupport<MyAdaptable> ads = new AdaptableSupport<MyAdaptable>(this);

      public <T> T getAdapter(AdapterKey<T> key){
        return ads.getAdapter(key);
      }

      ...
    }

#### AdapterStore

An `AdaptableStore` is an IAdaptable implementation that can be used standalone.

### Adapt.Inject

- package: org.eclipse.gef.common.adapt.inject

The Adapt.Inject package contains Google Guice-based support for injecting adapters into an IAdaptable. That is, if an IAdaptable implementation provides an @InjectAdapters annotation on its <T> setAdapter(TypeToken<T>, T, String) method, and if corresponding adapter (map) bindings qualified with an @AdapterMap annotation are provided within a com.google.inject.Module, adapter instances can automatically be injected into instances of the IAdaptable. It needs to be pointed out that respective adapter (map) bindings are evaluated polymorphically, i.e. a concrete adaptable will also be injected with all adapters that registered for super types of it.

In addition to basic injection support for adapters, the package also provides support for scoping all objects that are injected in the (transitive) context of an IAdaptable by means of a dedicated com.google.inject.Scope ( AdaptableScope).

#### AdapterInjectionSupport, AdaptableTypeListener, AdapterInjector

To enable injection of adapters to an IAdaptable, a specific com.google.inject.spi.TypeListener ( `AdaptableTypeListener`) needs to be registered in the com.google.inject.Module. To ensure this is done properly, a respective support com.google.inject.Module is provided, namely `AdapterInjectionSupport`, which can easily be integrated into a custom com.google.inject.Module as follows:

    public class MyModule extends AbstractModule {

      @Override
      protected void configure() {
        // register adapter map injection support
        install(new AdapterInjectionSupport());

        ...
      }
    }

This will ensure that the `AdaptableTypeListener` is properly registered (and itself injected). The `AdaptableTypeListener` will register a dedicated com.google.inject.MembersInjector ( `AdapterInjector`) on all suitable IAdaptable implementations it encounters.

#### @InjectAdapters

Specifying the injection point (i.e. the <T> setAdapter(TypeToken<T>, T, String) method within a respective IAdaptable implementation is achieved by adding an @InjectAdapters annotation as follows:

    public class MyAdaptable implements IAdaptable {

      @InjectAdapters
      public <T> void setAdapter(TypeToken<T> adapterType, T adapter, String role) {
        ...
      }
    }

#### AdapterMap, AdapterMaps

Specifying the to be injected adapters is performed by means of map bindings in the com.google.inject.Module, which are qualified with an @AdapterMap annotation. In case the actual type of the to be registered adapter cannot be inferred from the adapter instance itself, or from the respective binding, information about the actual adapter type has to be provided via the AdapterKey used in all bindings. Where the type of an adapter can be inferred from the instance or the binding itself, it may be omitted.

    public class MyModule extends AbstractModule {

      @Override
      protected void configure() {
        ...

       // obtain a map binder to bind adapters for the respective IAdaptable type.
       MapBinder<AdapterKey<?>, Object> adapterMapBinder = AdapterMaps.getAdapterMapBinder(binder(), MyAdaptable.class);

       // add adapter (map) binding for binding adapter 'a' of raw type 'A' with 'default' role to each MyAdaptable instance;
       // type information can be omitted, as it can be inferred from the adapter instance
       adapterMapBinder.addBinding(AdapterKey.defaultRole()).toInstance(a);

       // add adapter (map) binding for binding an instance of raw type 'A' with role 'r' to each MyAdaptable instance;
       // type information can be omitted, as it can be inferred from the binding
       adapterMapBinder.addBinding(AdapterKey.role("r").to(A.class);

       // add adapter (map) binding for binding adapter 'a' of parameterized type 'A<T>' with 'default' role to each MyAdaptable instance;
       // type information is required, as it cannot be inferred from the adapter instance, nor from the binding
       adapterMapBinder.addBinding(AdapterKey.get(new TypeToken<A<T>>(){})).toInstance(a);

       ...
      }
    }

When adapter map injection is properly enabled in the com.google.inject.Module, all suitable IAdaptable instances that are created through an com.google.inject.Injector, which is aware of the respective com.google.inject.Module, will be injected.

To this extend, the `@AdapterMap`-bindings can be compared to the Guice @Named-bindings, only that a java.lang.Class instead of a java.lang.String key is used. However, `@AdapterMap`-bindings are more powerful, as they are evaluated polymorphically. That is, if a binding is specified for a specific IAdaptable, let's say 'A', it will be evaluated for instances of all subtypes of 'A' as well, as long as they are suitable for injection (i.e. they directly or via inheritance provide a respective method eligible for adapter injection). This is a very powerful mechanism that is used intensively by the MVC component. It allows to register certain adapters already for some abstract base type, so that each concrete sub-type will be injected with a respective adapter instance.

In addition, adapter map bindings can be conditional, by qualifying them with a (transitive) adaptable type and role. The respective binding will then only be evaluated in case an adaptable of specified type (which is itself adapted under a specific role) exists in the adaptable-adapter chain of the adaptable that is to be injected. A potential use case is to bind different behaviors and policies for visual parts within respective viewers:

      // bindings related to GeometricShapePart within content viewer
      bindGeometricShapePartAdaptersInContentViewerContext(AdapterMaps.getAdapterMapBinder(
        binder(),
        GeometricShapePart.class,
        AdapterKey.get(IViewer.class, CONTENT_VIEWER_ROLE)));

      // bindings related to GeometricShapePart within palette viewer
      bindGeometricShapePartAdapterInPaletteViewerContext(AdapterMaps.getAdapterMapBinder(
        binder(),
        GeometricShapePart.class,
        AdapterKey.get(IViewer.class, PALETTE_VIEWER_ROLE)));

In case an adapter map binding is conditional, the AdapterInjector defers its injection until the complete adaptable-adapter chain has been established.

#### AdaptableScope, AdaptableScopes

An `AdaptableScope` is a Guice com.google.inject.Scope that is bound to an IAdaptable instance. It can be used to scope the object instances (not limited to adapters) during injection. To enable this, bindings have to be 'scoped' and the scope has to be entered for the respective IAdaptable instance before injection of adapters is triggered (which is supported best by using the `AdaptableScopes` support class).

Scoping bindings can simply be performed in a Guice com.google.inject.Module as follows:

    public class MyModule extends AbstractModule {

      @Override
      protected void configure() {
        ...

        // within the context of IAdaptable 'A', reuse a single instance of type 'B'
        binder().bind(B.class).in(AdaptableScopes.typed(A.class));

        ...
      }
    }

Entering the respective AdaptableScope is internally performed by the AdapterInjector.

### Attributes

- package: org.eclipse.gef.common.attributes

The Attributes package provides abstractions around string-key based (object) properties.

#### IAttributeStore

The `IAttributeStore` is a general abstraction that provides support for storing and retrieving java.lang.Object attributes via java.lang.String keys in the form of an (observable) map property.

#### IAttributeCopier

The `IAttributeCopier` is a general abstraction for a copier that can transfer/copy attributes from one IAttributeStore to another. It provides static `NULL_COPY` and `SHALLOW_COPY` default copier implementations.

### Beans.Binding

- package: org.eclipse.gef.common.beans.binding

The Beans.Binding package provides binding implementations for Google Guava's com.google.common.collect.Multiset and com.google.common.collect.SetMultimap collections, as well as replacements for JavaFX's (internal) expression helper classes, which are used by the JavaFX property replacement classes provided by Beans.Property.

### Beans.Property

- package: org.eclipse.gef.common.beans.property

The Beans.Property package provides (observable) property abstractions and implementations for Google Guava's com.google.common.collect.Multiset and com.google.common.collect.SetMultimap collections, as well as replacements for JavaFX's list, set, and map property base classes ( javafx.beans.property.ReadOnlyMapPropertyBase, javafx.beans.property.ReadOnlyListPropertyBase, javafx.beans.property.ReadOnlySetPropertyBase, javafx.beans.property.SimpleMapProperty, javafx.beans.property.SimpleListProperty, javafx.beans.property.SimpleSetProperty).

A good overview about how to use the properties provided by Beans.Property is given in GEF Common Collections and Properties - Guava goes FX.

### Beans.Value

- package: org.eclipse.gef.common.beans.value

The Beans.Value package provides ObservableValue and WritableValue abstractions related to Google Guava's com.google.common.collect.Multiset and com.google.common.collect.SetMultimap collections. These are implemented by the observable collections and properties provided by Collections and Beans.Property.

### Collections

- package: org.eclipse.gef.common.collections

The Collections package provides observable variants of Google Guava's com.google.common.collect.Multiset and com.google.common.collect.SetMultimap collections as well as a utility class via which these observable collection as well replacements for JavaFX's observable collections (that fix some issues) can be instantiated.

A good overview about how to use the collections provided by Collections and some insight about the additions and workarounds for the JavaFX provided collections is given in GEF Common Collections and Properties - Guava goes FX.

#### CollectionUtils

`CollectionUtils` is a utility class that augments javafx.collections.FXCollections. It provides static utility methods to create the observable equivalents for com.google.common.collect.Multiset and com.google.common.collect.SetMultimap, as well as the replacement classes for the JavaFX collections that are provided.

#### ObservableMultiset, ObservableMultisetWrapper, UnmodifiableObservableMultisetWrapper

`ObservableMultiset` is an observable variant of Google Guava's com.google.common.collect.Multiset in the style of a JavaFX observable collection. There are two concrete (internal) implementations, `ObservableMultisetWrapper` as well as `UnmodifiableObservableMultisetWrapper`, which should not be accessed directly but can be created using the utility operations provided by CollectionUtils.

#### ObservableSetMultimap, ObservableSetMultimapWrapper, UnmodifiableObservableSetMultimapWrapper

`ObservableSetMultimap` is an observable variant of com.google.common.collect.SetMultimap in the style of a JavaFX observable collection. There are two concrete (internal) implementations, `ObservableSetMultimapWrapper` as well as `UnmodifiableObservableSetMultimapWrapper`, which should not be accessed directly but can be created using the utility operations provided by CollectionUtils.

#### MultisetListenerHelper, SetMultimapListenerHelper

The `MultisetListenerHelper` and `SetMultimapListenerHelper` are (internal) delegate classes that are used internally by ObservableMultiset and \#ObservableSetMultimap, ObservableSetMultimapWrapper, UnmodifiableObservableSetMultimapWrapper |ObservableSetMultimap]], as well as the related properties and bindings within [Beans.Binding and Beans.Property to maintain and notify registered listeners.

#### ObservableListWrapperEx

`ObservableListWrapperEx` is an (internal) replacement class for the ObservableListWrapper returned by javafx.collections.FXCollections in its utility functions related to observable lists. It can be constructed using respective utility methods provided by CollectionUtils.

#### ListListenerHelperEx, SetListenerHelperEx, MapListenerHelperEx

The `ListListenerHelperEx`, `SetListenerHelperEx`, and `MapListenerHelperEx` are (internal) delegate classes that replace the respective delegate classes used internally by the JavaFX implementations provided for javafx.collections.ObservableList, javafx.collections.ObservableSet, and javafx.collections.ObservableMap. They are used by the ObservableListWrapperEx as well as the replacements provided by Beans.Binding and Beans.Property .

### Dispose

- package: org.eclipse.gef.common.dispose

The Dispose package provides an abstraction ( IDisposable) for objects that need to be notified when being disposed.

#### IDisposable

An `IDisposable` needs to be disposed. While the `IDisposable` encapsulates the necessary steps that have to be performed when being disposed, the initiation of the disposal is left to its clients.

### Reflect

- package: org.eclipse.gef.common.reflect

The Reflect package provides a utility class ( ReflectionUtils) that offers convenience operations in the context of Java reflection.

#### Types

The `Types` utilities provide support for handling different TypeToken implementations.

#### ReflectionUtils

The `ReflectionUtils` utilities provide support for getting and setting values of private fields by means of Java reflection.