arcgis-explorer-team

The Customizing ArcGIS Explorer Desktop Part 3 post introduced you to the steps you should follow to learn how to create add-ins. In this post we will run through a scenario in which we build an ArcGIS Explorer add-in, highlighting some common activities with the ArcGIS Explorer API along the way.

The scenario is that we would like to write an add-In which allows the user to draw a polygon on the map then use that shape to perform a spatial query against a layer in the map, and finally display the results as a new layer.

The first task is to decide which type of add-in will provide the right user experience for our users. Since the only interaction required from the user in this add-in is to draw a new polygon on the map, a Button add-in will be perfect.

The Button add-in class has an OnClick method which we override allowing us to implement some code which will respond to the user clicking our button on the ribbon. The first piece of code we write (in almost every add-in we create) will retrieve the ActiveMapDisplay. This can easily be done via the activeMapDisplay snippet provided with the ArcGIS explorer SDK in Visual Studio.

Next we will use the TrackPolygon() method on the MapDisplay class. This method puts the application into digitise mode and waits for the user to click on the map two or more times ending with a double click to create a polygon which is returned from the TrackPolygon call.

In order to perform the spatial query against the USA States layer we need to find that layer in the map. This is easily done with the convenient FindByName() method on the Map object (accessed via the MapDisplay). In this case we know it will definitely be a FeatureLayer and can safely cast it as such. FeatureLayers have a Table property which provides access to a Table object containing the actual data underlying the FeatureLayer.

The Table.Search() method is the reason we’re interested in the Table. In order to successfully use the Search() method we must provide a Filter object.  One of the options for creating a Filter object allows us to pass in a geometry to act as a spatial filter. In this case the user defined polygon has been provided as the input Geometry and the type Intersects as the FilterSearchOption. This will return all the features in the USA States layer which intersect the polygon the user drew on the map.

The Search() method returns a RowCollection which can be processed in a number of ways depending on your scenario. However, we would like to explore a new area of the API in the 1500 which provides support for filtering FeatureLayers directly via a new QueryDefinition property. In this scenario we loop through all the rows in the RowCollection to build up a comma separated string of ObjectIDs which can then be used with the “IN” SQL operator in a query string set as the QueryDefinition property.

Once the QueryDefinition property has been set on the FeatureLayer the SetSymbol() method can be used to define how the layer will appear in the map, in this case we chose a simple red outline. Finally we use the Connect() method on the FeatureLayer to check we can successfully connect to the underlying data source and if the response is true we add the layer to the map, inserting as the topmost layer.

In this blog post we have covered the process of implementing an ArcGIS Explorer Add-in right from choosing the right type of Visual Studio Add-in project appropriate for our purpose and overriding the OnClick method as the entry point for our code to writing some code which demonstrates several  activities commonly undertaken with the ArcGIS Explorer API. More information about the various pieces of the API we have used can be found in the SDK help: http://help.arcgis.com/en/arcgisexplorer/1500/sdk/index.html

Source code for this example can be downloaded from ArcGIS Online.

(Mike Branscomb & Mike Rudden - ArcGIS Explorer product engineers)