geoview

LegendsLayerSet Class

The LegendsLayerSet class is used to create objects that will keep legends associated with layer paths. It uses internally an instance of the LayerSet class to keep track of the layers loaded on the map. The property list of the LayerSet remains synchronized with all layer paths on the map at all times. However, the LayerSet has a registration condition function that filter out XYZ layers since they do not have an associated legend. If you delete or add a layer to the map, the LayerSet will be updated accordingly. The values associated with layer paths are of one of the following types: null, undefined or TypeLegend. A nullvalue means the getLegend call did not get the expected legend due to an error. The undefinedvalue is used to identify the layer paths that need to return there legend. A value of TypeLegend is the layer path legend. The structure of TypeLegend is shown below:

export type TypeLegend = {
  layerPath: string,
  layerName?: string,
  type: TypeGeoviewLayerType,
  styleConfig?: TypeStyleConfig,
  legend: TypeVectorLayerStyles | HTMLCanvasElement | null,
};

The layerPath parameter is used to link the legend to the layer entry configuration in the map. The layerName is a bilingual string for display information. The type tells us how to handle the legend. The styleConfig parameter contains the configuration settings that describe the style of the legend. This can be a simple, a unique value, or a class break configuration. Finally, we have the legend, whose null value indicates that it is impossible to get a legend for the layer. When the type is ogcWms, the legend is a HTMLCanvasElement. Otherwise, it is a TypeVectorLayerStyles.

 

The class can be instantiated using the constructor or the create method. At creation time, the constructor instantiates a LayerSet object which will send a LAYER_SET.REQUEST_LAYER_INVENTORY event using a mapId/LayerSetId handler in order to get the list of all the layerPaths existing on the map. Throughout its existence, the LegendsLayerSet instance listens, through its LayerSet property, to the LAYER_SET.LAYER_REGISTRATION events that are emitted when a layer is created/destroyed on the map or in response to the inventory request to update its ResultSet property. It also listens to the GET_LEGENDS.LEGEND_INFO event. This listener receives the legend information returned by the layer’s getLegend call and store it in the LayerSet. If all the registered layers have their legend information, a GET_LEGENDS.LEGEND_LAYERSET_UPDATED event is triggered with a mapId/LayerSetId handler.

When the LegendsLayerSet is created, a LAYER_SET.UPDATED listener is attached to the instance to wait for LayerSet modifications. Then, a GET_LEGENDS.QUERY_LEGEND event will be emited to all undefined legend of the LayerSet to obtain the legends.

The LAYER_SET.UPDATED listener will catch layer add/remove applied to the map. If a layer is added, a GET_LEGENDS.QUERY_LEGEND event will be emited for it and when all the registered layers have received their legend information, a GET_LEGENDS.LEGEND_LAYERSET_UPDATED event is emited using the mapId/LayerSetId as handler. The GET_LEGENDS.LEGEND_LAYERSET_UPDATED event is also emited when a layer is removed from the map to signal that a legend has been removed.

To see how you can use the FeatureInfoLayerSet, you can analyse the code of the following files:

• the constructor of the DetailsAPI class defined in packages/geoview-core/src/core/components/details/details/details-api.ts and its createDetails function; DEPRECATED
• the GET_FEATURE_INFO.ALL_QUERIES_DONE listener in the DetailsItem JSX.Element defined in packages\geoview-details-panel\src\details-item.tsx and the createDetails API call near the end of the file;
• the GET_FEATURE_INFO.ALL_QUERIES_DONE listener in the DetailsItem JSX.Element defined in packages\geoview-footer-panel\src\details-item.tsx and the createDetails API call near the end of the file.

LegendsLayerSet State Diagram

The life cycle of the LegendsLayerSet starts with the creation of a LayerSet object. This means that all the state transitions explained in the LayerSet state diagram are performed at creation time. To summarize what happens at this time, we must consider two cases:

• The LegendsLayerSet is instantiated before the associated map has created its layers and the layers will be added at the time of their creation.
• The LegendsLayerSet is instantiated when the associated map already has layers enabled and these will be added as a result of the inventory request made by the LegendsLayerSet when it is created.

All map layers added to the LegendsLayerSet will fetch their legend, but only when the LegendsLayerSet process has been triggered. As long as the TRIGGER event is not emitted, the collection of legends is not done.

Let’s follow the thread of events for the first case. We create a LegendsLayerSet. As a result, a LayerSet is instanciated to associate each layer path with its legend. The REQUEST_LAYER_INVENTORY event that is thrown at this point in time is done for nothing, because the map does not contain a layer. However, each time a layer is added to the map, a LAYER_REGISTRATION event is emited to add its layer path to the LayerSet. This action will trigger a LAYER_SET.UPDATED event to tell the LegendsLayerSet instance that its LayerSet has been modified. If the LegendsLayerSet has received its TRIGGER event, It will react to the Layer_set.updated and request the legend for the newly added layer path. It is the code of the layer path of the GeoView layer instance that will request the legend and when it is obtained, a LEGEND_INFO event will be emitted for the layer path of the map. This will update the LayerSet and if all legends are fetched, an LEGEND_LAYERSET_UPDATED event is emited to signal to all listening object that the legends has changed.

The second case differs from the previous one only in the way the REQUEST_LAYER_INVENTORY event is handled. Since layers already exist on the map, they will identify themselves for registration. The rest of the logic is the same.

 

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