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GEF/GEF4/MVC

< GEF‎ | GEF4

Note to non-wiki readers: This documentation is generated from the Eclipse wiki - if you have corrections or additions it would be awesome if you added them in the original wiki page.


Introduction

The GEF4 MVC component provides support for building up graphical editors and views based on a model-view-controller architecture and is the intended replacement for GEF (MVC) 3.x. It is internally composed out of four modules, which provide toolkit-independent base abstractions and implementations (MVC), JavaFX-specific specializations (MVC.FX), and Eclipse UI-integration for both (MVC.UI, MVC.FX.UI). In addition there is a deployed MVC Logo Example.

GEF4-Components-MVC.png


MVC

  • feature: org.eclipse.gef4.mvc
  • bundle: org.eclipse.gef4.mvc

The MVC plug-in offers those core concepts that are independent of any concrete rendering toolkit as well as of the Eclipse UI. As indicated by its name, the module provides a model-view-controller architecture that can be used to build up graphical editors and views. In good tradition with GEF (MVC) 3.x, 'controllers' are referred to as 'parts' (while the term 'visual part' instead of 'edit part' is used here, to depict that the MVC framework is not limited to editors alone).

A graphical application is thus composed of one or more viewers, where each viewer (IViewer) is populated by a set of visual parts (IVisualPart), which control the visuals that are rendered inside the viewer's controls. Those of the visual parts, which are responsible of controlling to be visualized contents, are referred to as content parts (IContentPart). They are accompanied by feedback parts (IFeedbackPart) and handle parts (IHandlePart), which do not control visualized contents but feedback or handle visuals that are needed for user interaction. All visual parts are arranged in a hierarchy (which resembles the hierarchy of visuals), which is rooted by a 'root part' (IRootPart).

Besides the parent-child relationship that establishes the hierarchy, visual parts may also be related to each other by means of an anchorage-anchor relationship. That is, a visual part that is placed at an arbitrary location within the hierarchy may be anchored on another anchorage part. As the visual part hierarchy has to correspond to the visual hierarchy, this mechanism is very useful when parts that control visuals that are placed in arbitrary places within the visual hierarchy have to be related to each other. In a graphical application that usually organizes visuals into layers, it can for instance be intensively used to update feedback or handles. By explicitly anchoring a feedback part on an underlying (anchorage) target content part, the feedback part inter alia obtains the necessary hooks to listen for changes of the content part visual (e.g. a position change) and to update its own feedback visual accordingly.

Tools (ITool) are used to interact with the parts inside a viewer. Each tool should be responsible of handling a certain interaction gesture (e.g. mouse click/drag or touch-based pinch/spread), by locating respective target parts (e.g. via hit-testing on the visual) and forwarding the interaction to them. While a tool should not have own interaction logic, it is responsible of handling the interaction, to which several parts may contribute e.g. by updating their contents, as a whole. That is, the tool has to ensure that all content modifying operations that result from a certain interaction, are executed in a single (undoable) transaction. As an interaction may span several viewers (e.g. a drag/drop operation), tools are bound to a domain (IDomain), to which also all viewers that make up a graphical application are bound, that maintains a global operation history and facilities to initialize and commit transactions.

The handling of an interaction is not performed directly by the target visual parts themselves, but by respective (interaction) policies (IPolicy) that are bound to them. An interaction policy is a strategy that encapsulates a certain (exchangeable) interaction logic, related to a gesture (e.g. what to do on click/drag). The active tool that handles an interaction takes this into account when forwarding the interaction, as it locates target parts also by evaluating their supported policies, and interacts with these policies directly. An (interaction) policy may handle an interaction directly, e.g. by manipulating the viewer state (e.g. changing the current selection when the target part gets clicked). It may also delegate to certain (transaction) policies that manipulate the contents as a result of an interaction (and have to do this by means of executing operations within the currently active transaction, the respective interaction tool has opened via the domain).

The viewer state (e.g. the current selection), which might be manipulated as the result of an interaction, is represented by means of dedicated models (ContentModel, SelectionModel, ViewportModel, etc.), which are bound to each viewer. As changes to the viewer state, as well as to the visualized contents, may lead to necessary viewer updates as well, behaviors (Behavior) may be bound to parts similar to policies. In contrast to policies, behaviors are active themselves, that is they will actively listen for changes (e.g. newly added content). Behaviors are also responsible of creating and disposing respective visual parts as needed (e.g. to update selection feedback as a result of changes to the selection model).


{Root}

  • package: org.eclipse.gef4.mvc

The root package contains a Guice Module which defines the default bindings for MVC.

MvcModule

The MvcModule defines methods to register bindings for different types (IBehavior, IVisualPart, etc.) which can be refined (overridden) by sub-classes. Additionally, it registers bindings for the ContentModel, ViewportModel, and GridModel.


Behaviors

  • package: org.eclipse.gef4.mvc.behaviors

The behaviors package contains the IBehavior and AbstractBehavior definitions. Additionally, it provides various IBehavior implementations and a utility class for IBehaviors.

IBehavior & AbstractBehavior

Every IBehavior is bound to an IVisualPart, referred to as the host of the behavior. A behavior is meant to be registering change listeners on a model (e.g. SelectionModel, ContentModel, etc.) during its activation (and unregistering them during its deactivation). It will then update another model (e.g. the visualization) based on the changes to the first model. For example, the SelectionBehavior registers a listener on the SelectionModel and generates (or removes) selection feedback based on the changes reported by the listener.

The AbstractBehavior handles activation and provides methods to add/remove feedback and handle parts using the IFeedbackPartFactory and IHandlePartFactory of the viewer.

BehaviorUtils

The BehaviorUtils class provides utility methods for establishing/unestablishing anchored-anchorage relations. These methods are used by the AbstractBehavior when adding/removing feedback or handles.

ContentBehavior

The ContentBehavior is listening for ContentModel changes to initiate a content synchronization upon changes. During a content synchronization, the currently active content parts are checked against the current content objects, i.e. content parts are created or removed based on the parent-child and anchored-anchorage relations between the content objects as defined by the content parts.

A content part that is removed is stored in a ContentPartPool, so that it can be re-used if it is needed later, and does not have to be re-created.

HoverBehavior

The HoverBehavior reacts to HoverModel changes. It can be bound to all content parts that should generate feedback/handles when the mouse hovers the part.

SelectionBehavior

The SelectionBehavior reacts to SelectionModel changes. It can be bound to all content parts that should generate feedback/handles when the part is selected.


Domain

  • package: org.eclipse.gef4.mvc.domain

The domain package contains the IDomain abstraction and its related AbstractDomain realization.

GEF4-MVC-domain.png

IDomain & AbstractDomain

The IDomain represents the collective state of an MVC application, i.e. it is composed of all viewers and tools. Additionally, the domain provides an operation history and undo context, which are used by policies to change the state of the application.



Models

  • package: org.eclipse.gef4.mvc.models

The models package contains all viewer models, i.e. the data constituting a viewer state.

GEF4-MVC-models.png

ContentModel

The ContentModel stores the viewer's contents, i.e. the data that is processed by your application.

FocusModel

The FocusModel stores the IVisualPart with keyboard focus, i.e. the part that will receive all keyboard input.

GridModel

The GridModel stores the viewer's background grid settings:

  • snap-to-grid, true or false, indicates whether the visualization should snap to grid points.
  • show-grid, true or false, indicates whether to show the grid, or not.
  • zoom-grid, true or false, indicates whether to zoom the grid, or not.
  • grid-cell-width, Double, specifies the width of grid cells.
  • grid-cell-height, Double, specifies the height of grid cells.

HoverModel

The HoverModel stores the currently hovered IVisualPart.

SelectionModel

The SelectionModel stores all currently selected IContentParts.

ViewportModel

The ViewportModel stores the current viewport information, i.e. a scroll offset and a viewport transformation.


Operations

  • package: org.eclipse.gef4.mvc.operations

The operations package contains implementations of IUndoableOperation which can be used to manipulate the default models, especially content creation and removal.

AbstractCompositeOperation

The AbstractCompositeOperation is the base class for the two composite operation implementations: ForwardUndoCompositeOperation and ReverseUndoCompositeOperation. A composite operation is composed of a number of IUndoableOperations.

AddContentChildOperation

The AddContentChildOperation can be used to add a content child to an IContentPart. It relies on the IContentPart#addContentChild() method for doing this.

This operation is the counterpart of the RemoveContentChildOperation.

AttachToContentAnchorageOperation

The AttachToContentAnchorageOperation can be used to attach an IContentPart to a content anchorage. It relies on the IContentPart#attachToContentAnchorage() method for doing this.

This operation is the counterpart of the DetachFromContentAnchorageOperation.

ChangeFocusOperation

The ChangeFocusOperation can be used to set the currently focused part by manipulating the FocusModel.

ChangeHoverOperation

The ChangeHoverOperation can be used to set the currently hovered part by manipulating the HoverModel.

ChangeSelectionOperation

The ChangeSelectionOperation can be used to set the currently selected parts by manipulating the SelectionModel.

ClearHoverFocusSelectionOperation

The ClearHoverFocusSelectionOperation can be used to clear the HoverModel, FocusModel, and SelectionModel, i.e. no parts will be focused, hovered, or selected after executing this operation.

DetachFromContentAnchorageOperation

The DetachFromContentAnchorageOperation can be used to detach an IContentPart from a content anchorage. It relies on the IContentPart#detachFromContentAnchorage() method for doing this.

This operation is the counterpart of the AttachToContentAnchorageOperation.

ForwardUndoCompositeOperation

The ForwardUndoCompositeOperation extends the AbstractCompositeOperation. It will execute(), redo(), and undo() its operations in the order they were added to the composite operation.

RemoveContentChildOperation

The RemoveContentChildOperation can be used to remove a content child from an IContentPart. It relies on the IContentPart#removeContentChild() method for doing this.

This operation is the counterpart of the AddContentChildOperation.

ReverseUndoCompositeOperation

The ReverseUndoCompositeOperation extends the AbstractCompositeOperation. It will execute() and redo() its operations in the order they were added to the composite operation, however it will undo() its operations in reverse order.

SetRefreshVisualOperation

The SetRefreshVisualOperation can be used to enable/disable the IVisualPart#refreshVisual() method for a specific IVisualPart.

SynchronizeContentAnchoragesOperation

The SynchronizeContentAnchoragesOperation can be used to initiate a synchronization of the content anchorages and currently active IContentParts for a given anchored IContentPart.

SynchronizeContentChildrenOperation

The SynchronizeContentChildrenOperation can be used to initiate a synchronization of the content children and currently active IContentParts for a given parent IContentPart.

UnexecutableOperation

The UnexecutableOperation is an "empty" operation, i.e. it will not do anything. However, since it is unexecutable, every composite operation containing an UnexecutableOperation is unexecutable, too.

ITransactional

The ITransactional interface defines two methods init() and commit() : IUndoableOperation which enclose a transaction. Therefore, an ITransactional can be used to retrieve an operation which performs specific changes. For example, an IPolicy that implements ITransactional would probably create an IUndoableOperation within init(), manipulate that operation within other methods, and finally return it from commit().


Parts

  • package: org.eclipse.gef4.mvc.parts

This package contains all abstractions related to controllers (aka parts) in a model-view-controller architecture. For each abstraction, a corresponding (abstract) realization is provided, from which specific controllers can be sub-classed.

GEF4-MVC-parts-abstractions.png

IVisualPart & AbstractVisualPart

The IVisualPart interface is the main MVC abstraction for controller objects, and therefore, controls a visual and handles user interaction. Visual parts are organized in a hierarchy, i.e. every part (except the root part) is associated with a parent part, and can control a number of children parts. Additional to the parent-child relations, visual parts can be part of anchored-anchorage relations, which are independent to the hierarchy, i.e. anchoreds and anchorages can be located at arbitrary places within the hierarchy.

Visual parts are adaptable, so that you can adapt policies and behaviors to them (as well as anything else if needed). This is an integral part of user interaction, because the tools will delegate input events to corresponding policies of the visual part which controls the event target (visual). Visual parts are also activatable. During activation/deactivation they will activate/deactivate their adapters.

Moreover, a visual part is an IPropertyChangeNotifier, i.e. it will notify all registered listeners about the following property changes:

  • "active": This visual part was activated/deactivated.
  • "adapters": The adapters (policies, behaviors, etc.) of this visual part changed.
  • "parent": The parent of this visual part changed.
  • "children": The children of this visual part changed.
  • "anchorages": The anchorages of this visual part changed.
  • "anchoreds": The anchoreds of this visual part changed.

IRootPart & AbstractRootPart

The IRootPart interface is a specialization of the IVisualPart interface. There is exactly one root part per viewer, and it manages the content parts, feedback parts, and handle parts, as well as the root visuals.

IContentPart & AbstractContentPart

The IContentPart interface is a specialization of the IVisualPart interface. Content parts are bound to content model elements, i.e. they provide a link to the model, and allow manipulations of the model via IContentPart#addContentChild(), IContentPart#removeContentChild(), IContentPart#attachToContentAnchorage(), and IContentPart#detachFromContentAnchorage().

IFeedbackPart & AbstractFeedbackPart

The IFeedbackPart interface is a specialization of the IVisualPart interface. Feedback parts are used to give visual feedback to the user during interactions. They are usually rendered on top of the content parts.

IHandlePart & AbstractHandlePart

The IHandlePart interface is a specialization of the IVisualPart interface. Handle parts are used for visual handles, which can be used for interaction, i.e. to manipulate elements. They are usually rendered on top of the feedback parts.

IContentPartFactory

The IContentPartFactory interface is part of a default mechanic in MVC: It is used during the content synchronization within the ContentBehavior to create new content parts. Therefore, if you want to use this default mechanic, you have to supply an IContentPartFactory suitable to your content model.

IFeedbackPartFactory

The IFeedbackPartFactory interface is part of a default mechanic in MVC: It is used for creating feedback parts within the default behaviors, i.e. in response to mouse hover or selection changes.

IHandlePartFactory

The IHandlePartFactory interface is part of a default mechanic in MVC: It is used for creating handle parts within the default behaviors, i.e. in response to mouse hover or selection changes.

PartUtils

The PartUtils class is a collection of utility methods when working with visual parts.


Policies

  • package: org.eclipse.gef4.mvc.policies

The policies package contains the IPolicy (and AbstractPolicy) abstraction and concrete implementations for the manipulation of the ContentModel: ContentPolicy, CreationPolicy, and DeletionPolicy.

IPolicy & AbstractPolicy

The IPolicy interface is similar to the IBehavior interface in that it is bound to an IVisualPart. However, behaviors start actions by themselves (they are active), while policies are always called from the outside (they are passive). Policies can be used to contribute arbitrary functionality to a visual part, which can then be used by other parts of the application. For example, tools usually delegate input events to suitable policies on the visual part which controls the visual which received the input event.

ContentPolicy

The ContentPolicy is a transactional (see ITransactional) policy to handle content changes, i.e. adding/removing of content children, as well as attaching/detaching to/from content anchorages. Therefore, it can be used to retrieve an operation which performs the desired content changes.

CreationPolicy

The CreationPolicy is a transactional (see ITransactional) policy that handles the creation of new content objects using the ContentPolicy. Therefore, it can be used to retrieve an operation which performs the desired creations.

DeletionPolicy

The DeletionPolicy is a transactional (see ITransactional) policy that handles the deletion of existing content objects using the ContentPolicy. Therefore, it can be used to retrieve an operation which performs the desired deletions.


Tools

  • package: org.eclipse.gef4.mvc.tools

The tools package contains the ITool abstraction and its related AbstractTool realization.

GEF4-MVC-tools.png

ITool & AbstractTool

An ITool delegates certein input events or model changes to a corresponding (interaction) policy.


Viewer

  • package: org.eclipse.gef4.mvc.viewer

The viewer package contains the IViewer abstraction and the related AbstractViewer realization.

GEF4-MVC-viewer.png

IViewer & AbstractViewer

An IViewer is the container for a visual part hierarchy and provides a link to the domain.


MVC.FX

  • feature: org.eclipse.gef4.mvc.fx
  • bundle: org.eclipse.gef4.mvc.fx

The MVC.FX module provides specializations of the abstractions and implementations provided by MVC, which are bound to JavaFX-based visualizations.


{Root}

  • package: org.eclipse.gef4.mvc.fx

The root pacakge contains a Guice Module with default bindings for MVC.FX.

MvcFxModule

The MvcFxModule extends the MvcModule. It defines methods to register bindings for the JavaFX-specific extensions to MVC (AbstractFXVisualPart, FXViewer, etc.) which can be refined (overridden) by sub-classes. Additionally, it registers the following bindings per default:

  • AbstractFXContentPart adapter bindings: FXTransformProvider, ContentBehavior, HoverBehavior, SelectionBehavior, FXFocusBehavior, and ContentPolicy.
  • AbstractFXHandlePart adapter bindings: FXHoverOnHoverPolicy and HoverBehavior.
  • FXDomain adapter bindings: FXHoverTool, FXClickDragTool, FXTypeTool, FXRotateTool, FXPinchSpreadTool, FXScrollTool, and FXFocusTool.
  • FXRootPart adapter bindings: FXFocusAndSelectOnClickPolicy, FXMarqueeOnDragPolicy, FXHoverOnHoverPolicy, FXZoomOnScrollPolicy, FXZoomOnPinchSpreadPolicy, FXPanOnScrollPolicy, FXPanOnTypePolicy, FXRotateSelectedOnRotatePolicy, FXChangeViewportPolicy, ContentBehavior, SelectionBehavior, FXGridBehavior, and FXViewportBehavior.
  • FXViewer adapter bindings: IRootPart, FocusModel, HoverModel, and SelectionModel.

Behaviors

  • package: org.eclipse.gef4.mvc.fx.behaviors

The behaviors package contains JavaFX/MVC.FX-specific IBehavior implementations.

FXCursorBehavior

The FXCursorBehavior is listening for mouse and keyboard input, so that it can change the JavaFX mouse cursor when the user presses/releases a key while moving the mouse.

FXFocusBehavior

The FXFocusBehavior is listening for FocusModel changes and transfers them over to JavaFX.

FXGridBehavior

The FXGridBehavior is listening for GridModel changes in order to apply those changes to the GridLayout of the viewer.

FXHoverBehavior

The FXHoverBehavior is listening for HoverModel changes in order to generate feedback/handles when hovering a part.

FXViewportBehavior

The FXViewportBehavior is listening for ViewportModel changes and transfers them over to the ScrollPaneEx of the viewer.


Domain

  • package: org.eclipse.gef4.mvc.fx.domain

org.eclipse.gef4.mvc.fx.domain contains a JavaFX-specific IDomain implementation.

FXDomain

The FXDomain parameterizes the AbstractDomain with JavaFX Node, but does not extend it further.


Operations

  • package: org.eclipse.gef4.mvc.fx.operations

org.eclipse.gef4.mvc.fx.operations contains all IUndoableOperation implementations contributed by MVC.FX.

FXBendOperation

The FXBendOperation can be used to manipulate the points constituting an {@link FXConnection}, i.e. its start point, way points, and end point. When manipulating the start or end point, it does also connect it to the IVisualPart under mouse when applicable.

FXChangeViewportOperation

The FXChangeViewportOperation can be used to manipulate the ViewportModel, i.e. the scroll offset and content transformation.

FXResizeNodeOperation

The FXResizeNodeOperation can be used to resize a JavaFX Node.

FXRevealOperation

The FXRevealOperation can be used to reveal an IVisualPart in its IViewer.

FXTransformOperation

The FXTransformOperation can be used to manipulate the transformation associated with an IVisualPart due to FXTransformProvider.


Parts

  • package: org.eclipse.gef4.mvc.fx.parts

org.eclipse.gef4.mvc.fx.parts contains all IContentPart, IVisualPart, IFeedbackPart, and IHandlePart implementations and related classes.

AbstractFXContentPart

AbstractFXFeedbackPart

FXHoverFeedbackPart

FXSelectionFeedbackPart

FXSelectionLinkFeedbackPart

AbstractFXHandlePart

AbstractFXSegmentHandlePart

FXCircleSegmentHandlePart

FXRectangleSegmentHandlePart

AbstractFXRootPart

FXRootPart

FXDefaultFeedbackPartFactory

FXDefaultHandlePartFactory

ChopBoxAnchorProvider

FXTransformProvider

VisualBoundsGeometryProvider

VisualOutlineGeometryProvider


Policies

  • package: org.eclipse.gef4.mvc.fx.policies

org.eclipse.gef4.mvc.fx.policies contains all IPolicy implementations contributed by MVC.FX.

AbstractFXOnClickPolicy

AbstractFXOnDragPolicy

AbstractFXOnHoverPolicy

AbstractFXOnPinchSpreadPolicy

AbstractFXOnRotatePolicy

AbstractFXOnScrollPolicy

AbstractFXOnTypePolicy

FXBencOnSegmentHandleDragPolicy

FXBendPolicy

FXChangeViewportPolicy

FXDeleteSelectedOnTypePolicy

FXFocusAndSelectOnClickPolicy

FXHoverOnHoverPolicy

FXMarqueeOnDragPolicy

FXPanOnScrollPolicy

FXPanOnTypePolicy

FXRelocateConnectionPolicy

FXRelocateOnDragPolicy

FXResizePolicy

FXResizeRelocateOnHandleDragPolicy

FXResizeRelocatePolicy

FXRotatePolicy

FXRotateSelectedOnHandleDragPolicy

FXRotateSelectedOnRotatePolicy

FXScaleRelocateOnHandleDragPolicy

FXScaleRelocatePolicy

FXTransformPolicy

FXZoomOnPinchSpreadPolicy

FXZoomOnScrollPolicy


Tools

  • package: org.eclipse.gef4.mvc.fx.tools

org.eclipse.gef4.mvc.fx.tools contains JavaFX-specific ITool implementations for different interactions (e.g. mouse drag).

FXClickDragTool

FXFocusTool

FXHoverTool

FXPinchSpreadTool

FXRotateTool

FXScrollTool

FXTypeTool


Viewer

  • package: org.eclipse.gef4.mvc.fx.viewer

org.eclipse.gef4.mvc.fx.viewer contains a JavaFX-specific IViewer implementation.

FXViewer

ISceneContainer

FXStageSceneContainer


MVC.UI

  • feature: org.eclipse.gef4.mvc.ui
  • bundle: org.eclipse.gef4.mvc.ui

The MVC.UI module provides aspects for an integration into the Eclipse UI:

  • Binding the operation history from the Eclipse Workbench.
  • An UndoablePropertySheetPage for contribution to the "Properties View".

MVC.FX.UI

  • feature: org.eclipse.gef4.mvc.fx.ui
  • bundle: org.eclipse.gef4.mvc.fx.ui

The MVC.FX.UI module provides JavaFX-specific aspects for an integration into the Eclipse UI:

  • org.eclipse.gef4.mvc.fx.ui contains a Guice Module which binds an Eclipse ISelectionProvider and handles the construction of an FXCanvas to render the JavaFX scene graph.
  • org.eclipse.gef4.mvc.fx.ui.parts contains spcific Eclipse ViewPart and EditorPart implementations which wrap an FXCanvas.
  • org.eclipse.gef4.mvc.fx.ui.properties contains helper classes for the integration and manipulation of properties within the Eclipse "Properties View".
  • org.eclipse.gef4.mvc.fx.ui.viewer provides an ISceneContainer implementation for the propagation of a JavaFX Scene to an FXCanvas.

Migration from GEF (MVC) 3.x to MVC, MVC.FX, MVC.UI, MVC.FX.UI

GEF4 MVC was written completely from scratch. While some proven concepts have been transferred from GEF (MVC) 3.x, central concepts and mechanisms have been reworked. The most notable differences are:

  • More modularity, separating out Eclipse Workbench UI dependencies: While GEF (MVC) 3.x provided a single bundle (with Eclipse UI dependencies), GEF4 MVC clearly separates out those dependencies into the MVC.UI and MVC.FX.UI bundles, so that standalone graphical applications can be realized based on MVC and MVC.FX alone. Furthermore, rendering toolkit independent abstractions (provided by MVC) are now clearly separated from rendering toolkit (i.e. JavaFX) specific concretizations (provided by MVC.FX.
  • Usage of JavaFX instead of SWT/Draw2d.
  • Usage of adapter pattern throughout: While GEF (MVC) 3.x only used the Eclipse Platform provided adaptable pattern for Eclipse Workbench UI integration tasks (e.g. integration with properties view), this mechanism is used intensively within GEF4 MVC to configure the complete graphical application. That is, tools and viewers are adapted to the domain, viewer models and the root part are adapted to the viewer, policies and behaviors are adapted to visual parts.
  • Usage of dependency injection
  • Own visual parts for feedback and handles (compared to 'lightweight' feedback)
  • Separation of policies (passive, invoked by tools) and behaviors (active, listening for changes)
  • Separation of interaction policies (directly invoked by tools, related to interaction) and transaction policies (called by interaction policies, realize the content manipulation)
  • Pure interaction-gesture-based tools without own transactional logic (compared to monolithic 'selection tool'): In contrast to GEF (MVC) 3.x, where tools were dedicated to certain semantic operations (creation, selection, etc.), tools are now pretty dumb and dedicated to interaction gestures (click/drag, scroll, etc.), and forward all interactions to respective interaction policies. While the tools provides the transactional context (i.e. it opens and closes a respective operation via the domain, so that all operations that are executed as a result of the interaction can be undone together) they do not translate the gesture-based interaction into semantical operations themselves. This responsibility lies with the interaction policies alone. Where a GEF (MVC) 3.x application had thus to specialize one of the default tools to add different semantic behavior, this can now be achieved by registering different interaction policies, which is much more lightweight.