# Extensible Persistent State

Editor pages are able to persist user interface state between sessions independent of the data that is being edited. What state is persisted is dependent on editor page type. Two common examples of persistent state are sizing of resizable elements and selection. The persistent state is now extensible, allowing adopters to persist custom data.

The recommended approach is to extend the page's persistent state element type to add custom properties. The custom element type for persistent state is specified in sdef.

Example

In the catalog sample, a toggle action controls whether the manufacturer name is shown in the catalog item label. The state of this toggle is persisted by extending the state of the editor page. The persistent state is also used for communication between the toggle and the item label.

    public interface CatalogEditorPageState extends MasterDetailsEditorPageState
    {
        ElementType TYPE = new ElementType( CatalogEditorPageState.class );

        // *** ShowManufacturer ***

        @Type( base = Boolean.class )
        @DefaultValue( text = "false" )

        ValueProperty PROP_SHOW_MANUFACTURER = new ValueProperty( TYPE, "ShowManufacturer" );

        Value<Boolean> getShowManufacturer();
        void setShowManufacturer( String value );
        void setShowManufacturer( Boolean value );
    }

The custom state element type is attached to the editor page in sdef.

    <editor-page>
        <persistent-state-element-type>org.eclipse.sapphire.samples.catalog.CatalogEditorPageState</persistent-state-element-type>
    </editor-page>

The toggle action handler only interacts with the editor page state.

    public final class ShowManufacturerActionHandler extends SapphireActionHandler
    {
        private CatalogEditorPageState state;

        @Override
        public void init( final SapphireAction action, final ActionHandlerDef def )
        {
            super.init( action, def );

            this.state = (CatalogEditorPageState) getPart().nearest( SapphireEditorPagePart.class ).state();

            final Listener listener = new FilteredListener<PropertyContentEvent>()
            {
                @Override
                protected void handleTypedEvent( final PropertyContentEvent event )
                {
                    setChecked( ShowManufacturerActionHandler.this.state.getShowManufacturer().getContent() );
                }
            };

            this.state.attach( listener, CatalogEditorPageState.PROP_SHOW_MANUFACTURER );

            setChecked( this.state.getShowManufacturer().getContent() );

            attach
            (
                new FilteredListener<DisposeEvent>()
                {
                    @Override
                    protected void handleTypedEvent( final DisposeEvent event )
                    {
                        ShowManufacturerActionHandler.this.state.detach( listener, CatalogEditorPageState.PROP_SHOW_MANUFACTURER );
                    }
                }
            );
        }

        @Override
        protected Object run( final SapphireRenderingContext context )
        {
            this.state.setShowManufacturer( ! this.state.getShowManufacturer().getContent() );

            return null;
        }
    }

The toggle action and its handler are defined in sdef.

    <editor-page>
        <action>
            <id>Sample.ShowManufacturer</id>
            <label>Show Manufacturer</label>
            <image>ShowManufacturer.png</image>
            <type>TOGGLE</type>
            <context>Sapphire.EditorPage</context>
            <location>before:Sapphire.Outline.Hide</location>
        </action>
        <action-handler>
            <action>Sample.ShowManufacturer</action>
            <id>Sample.ShowManufacturer</id>
            <impl>ShowManufacturerActionHandler</impl>
        </action-handler>
    </editor-page>

Finally, the content outline node label for a catalog item is defined using an expression that reads the editor page state to determine whether to include the manufacturer in the label. The label automatically updates when any of the properties utilized in the expression are changed.

    <node-factory>
        <property>Items</property>
        <case>
            <label>${ Name == null ? "<item>" : ( State().ShowManufacturer && Manufacturer != null ? Concat( Manufacturer, " ", Name ) : Name ) }</label>
        </case>
    </node-factory>

Alternatively, custom state can be stored as arbitrary key-value pairs without extending the persistent state element. All of the system-provided state element types include an Attributes property for this purpose. To make it easier to work with the Attributes property, methods are provided to read and write attributes by name. These methods leverage all conversions known to Sapphire, so it is typically not necessary to manually convert the values to and from a string.

This approach should only be used in situations when extending the persistent state element is not practical or possible. State stored as attributes is harder to access. For instance, unlike actual properties, attributes cannot be directly accessed from EL.

Example

In the catalog sample, a toggle action controls whether the catalog items are color-coded by manufacturer. The state of this toggle is persisted as an attribute.

    public final class ShowManufacturerColorActionHandler extends SapphireActionHandler
    {
        public static final String ATTRIBUTE = "ColorCode";

        private CatalogEditorPageState state;

        @Override
        public void init( final SapphireAction action, final ActionHandlerDef def )
        {
            super.init( action, def );

            this.state = (CatalogEditorPageState) getPart().nearest( SapphireEditorPagePart.class ).state();

            final Listener listener = new FilteredListener<PropertyContentEvent>()
            {
                @Override
                protected void handleTypedEvent( final PropertyContentEvent event )
                {
                    setChecked( ShowManufacturerColorActionHandler.this.state.getAttribute( ATTRIBUTE, false ) );
                }
            };

            this.state.attach( listener, CatalogEditorPageState.PROP_ATTRIBUTES.getName() + "/*" );

            setChecked( this.state.getAttribute( ATTRIBUTE, false ) );

            attach
            (
                new FilteredListener<DisposeEvent>()
                {
                    @Override
                    protected void handleTypedEvent( final DisposeEvent event )
                    {
                        ShowManufacturerColorActionHandler.this.state.detach( listener, CatalogEditorPageState.PROP_ATTRIBUTES.getName() + "/*" );
                    }
                }
            );
        }

        @Override
        protected Object run( final SapphireRenderingContext context )
        {
            this.state.setAttribute( ATTRIBUTE, ! this.state.getAttribute( ATTRIBUTE, false ) );

            return null;
        }
    }

The toggle action and its handler are defined in sdef.

    <editor-page>
        <action>
            <id>Sample.ShowManufacturerColor</id>
            <label>Color Code Manufacturers</label>
            <image>ItemPurple.png</image>
            <type>TOGGLE</type>
            <context>Sapphire.EditorPage</context>
            <location>after:Sample.ShowManufacturer</location>
            <location>before:Sapphire.Outline.Hide</location>
        </action>
        <action-handler>
            <action>Sample.ShowManufacturerColor</action>
            <id>Sample.ShowManufacturerColor</id>
            <impl>ShowManufacturerColorActionHandler</impl>
        </action-handler>
    </editor-page>

A custom EL function is used to read the state attribute and to derive a color code item image based on the manufacturer.

    public final class ItemImageFunction extends Function
    {
        private final ImageData IMAGE_GENERIC = ImageData.createFromClassLoader( ItemImageFunction.class, "Item.png" );

        private final ImageData[] IMAGES =
        {
            ImageData.createFromClassLoader( ItemImageFunction.class, "ItemBlue.png" ),
            ImageData.createFromClassLoader( ItemImageFunction.class, "ItemGreen.png" ),
            ImageData.createFromClassLoader( ItemImageFunction.class, "ItemOrange.png" ),
            ImageData.createFromClassLoader( ItemImageFunction.class, "ItemPurple.png" ),
            ImageData.createFromClassLoader( ItemImageFunction.class, "ItemRed.png" ),
            ImageData.createFromClassLoader( ItemImageFunction.class, "ItemTurquoise.png" ),
            ImageData.createFromClassLoader( ItemImageFunction.class, "ItemYellow.png" )
        };

        @Override
        public String name()
        {
            return "CatalogItemImage";
        }

        @Override
        public FunctionResult evaluate( final FunctionContext context )
        {
            if( context instanceof PartFunctionContext )
            {
                final SapphirePart part = ( (PartFunctionContext) context ).part();
                final MasterDetailsEditorPagePart page = part.nearest( MasterDetailsEditorPagePart.class );

                if( page != null )
                {
                    final Element element = part.getLocalModelElement();

                    if( element instanceof Item )
                    {
                        final Item item = (Item) element;
                        final MasterDetailsEditorPageState state = page.state();

                        return new FunctionResult( this, context )
                        {
                            private Listener listener;

                            @Override
                            protected void init()
                            {
                                this.listener = new FilteredListener<PropertyContentEvent>()
                                {
                                    @Override
                                    protected void handleTypedEvent( final PropertyContentEvent event )
                                    {
                                        refresh();
                                    }
                                };

                                state.attach( this.listener, MasterDetailsEditorPageState.PROP_ATTRIBUTES.getName() + "/*" );
                                element.attach( this.listener, Item.PROP_MANUFACTURER );
                            }

                            @Override
                            protected Object evaluate()
                            {
                                final boolean color = state.getAttribute( ShowManufacturerColorActionHandler.ATTRIBUTE, false );

                                if( color )
                                {
                                    final String manufacturer = item.getManufacturer().getContent();
                                    final int hashCode = ( manufacturer == null ? 0 : manufacturer.hashCode() );
                                    final int index = abs( hashCode ) % IMAGES.length;

                                    return IMAGES[ index ];
                                }
                                else
                                {
                                    return IMAGE_GENERIC;
                                }
                            }

                            @Override
                            public void dispose()
                            {
                                super.dispose();

                                if( this.listener != null )
                                {
                                    state.detach( this.listener, MasterDetailsEditorPageState.PROP_ATTRIBUTES.getName() + "/*" );
                                    element.detach( this.listener, Item.PROP_MANUFACTURER );

                                    this.listener = null;
                                }
                            }
                        };
                    }
                }
            }

            throw new FunctionException( "CatalogItemImage() function cannot be used in this context.");
        }
    }

The CatalogItemImage() function is registered as a Sapphire extension.

    <extension>
        <function>
            <name>CatalogItemImage</name>
            <impl>org.eclipse.sapphire.samples.catalog.ItemImageFunction</impl>
        </function>
    </extension>

Finally, the content outline node image for a catalog item is defined using a simple expression that references the CatalogItemImage() function.

    <node-factory>
        <property>Items</property>
        <case>
            <image>${ CatalogItemImage() }</image>
        </case>
    </node-factory>

Copyright (c) 2015 Oracle
Content made available under the terms of Eclipse Public License.