geoview

FeatureInfoLayerSet Class

The FeatureInfoLayerSet class is used to create objects that will keep query results 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 all layers that are not queryable as defined in their metadata or configuration. If you delete or add a layer to the map, the LayerSet will be updated. The feature information is stored in the resultSet property and has a TypeFeatureInfoResultSet type which is an object whose properties are layer paths and the values are of one of the following types: null, undefined or TypeArrayOfFeatureInfoEntries. A nullvalue means the getLgetFeatureInfo call did not get the expected data due to an error. The undefinedvalue is used to identify the layer paths that need to return there result set. A value of TypeArrayOfFeatureInfoEntries is the layer path result set. The structure of TypeArrayOfFeatureInfoEntries is shown below:

export type TypeArrayOfFeatureInfoEntries = TypeFeatureInfoEntry[];

export type TypeFeatureInfoEntry = {
  featureKey: number,
  geoviewLayerType: TypeGeoviewLayerType,
  extent: Extent,
  geometry: Feature | null,
  featureIcon: HTMLCanvasElement,
  fieldInfo: Partial<Record<string, TypeFieldEntry>>,
  nameField: string | null,
};

export type TypeFieldEntry = {
  fieldKey: number,
  value: unknown,
  dataType: "string" | "date" | "number",
  alias: string,
  domain: null | codedValueType | rangeDomainType,
};

The featureKey property is a sequence number assigned to the row in the array. The geoviewLayerType property identifies the of GeoView layer type that returned the information. The extent property is the bounding box for the feature stored in the array row. The geometry is the feature object used to draw on the layer. The featureIcon is a snippet representation of the feature. Finally, the fieldInfo is an object whose properties are the field name as used internally and whose values are records of type TypeFieldEntry.

In a field entries, the fieldKey property is a sequence number assigned to the field. The value property is the actual value assigned to the field. The dataType property is the type of the value property. The alias is an alternative name for the field. Finally, domain is an object used by ESRI layers to describe the domain of values that can be assigned to the field value. When the value of geoviewLayerType is esriDynamic or esriFeature, you can use the domain property. Otherwise, you cannot.

 

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 layer paths already placed on the map. Throughout its existence, the FeatureInfoLayerSet 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_FEATURE_INFO.QUERY_RESULT event. This listener receives the feature information returned by the layer’s getFeatureInfo calls and store it in the LayerSet. If all the registered layers have their feature information, a GET_FEATURE_INFO.ALL_QUERIES_DONE event is triggered with a mapId/LayerSetId handler.

When created, the FeatureInfoLayerSet start listening for MAP.EVENT_MAP_SINGLE_CLICK events. When the user click on the map, a GET_FEATURE_INFO.QUERY_LAYER event is thrown to the map with the click position as a payload. This event will trigger the get feature info on the listening layers and when the query result is returned, it is relayed to the FeatureInfoLayerSet using a GET_FEATURE_INFO.QUERY_RESULT event.

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

FeatureInfoLayerSet State Diagram

The life cycle of the FeatureInfoLayerSet 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:

All map layers added to the FeatureInfoLayerSet will fetch their feature information on user map click.

Let’s follow the thread of events for the first case. We create a FeatureInfoLayerSet. As a result, a LayerSet is instanciated to associate each layer path with its feature info result set array. 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 FeatureInfoLayerSet instance that its LayerSet has been modified. It is the code of the layer path of the GeoView layer instance that will request the feature information when the users issue a click on the map and when the query result is obtained, a QUERY_RESULT event will be emitted for the layer path of the map. This will update the LayerSet and if all feature info array are fetched, an ALL_QUERIES_DONE event is emited to signal to all listening object that all feature info layer sets are received.

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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