HERE Android SDK Developer's Guide

Map Download by Specifying a Bounding Box or Route

Map data can be fetched into a persistent 256 MB cache to enable offline map capabilities by specifying a bounding box or radius around a route. This can be done through the MapDataPrefetcher and associated classes. The MapDataPrefetcher provides a set of methods to estimate the size of fetches (in KB), initiate fetches, cancel fetches, and clear the map data cache.

MapDataPrefetcher and MapDataPrefetcher.Listener Interfaces

MapDataPrefetcher is a singleton that can be obtained using the MapDataPrefetcher.getInstance() method. MapEngine must be successfully initialized before this method can be used. The next examples shows basic MapDataPrefetcher use.

To check for the size of the data in advance, use the estimateMapDataSize(GeoBoundingBox) or estimateMapDataSize(Route, int) methods:
GeoBoundingBox bbox = ...
MapDataPrefetcher.Request request =
  MapDataPrefetcher.getInstance( ).estimateMapDataSize(bbox);
...

To start MapDataPrefetcher fetch, use fetchMapData(GeoBoundingBox) or fetchMapData(Route, int):

GeoBoundingBox bbox = ...
MapDataPrefetcher.Request.Error error = MapDataPrefetcher .Request.Error.None;
MapDataPrefetcher.Request request = MapDataPrefetcher.getInstance( ).fetchMapData(bbox);
...

To cancel MapDataPrefetcher fetch, call cancelRequest(id)

MapDataPrefetcher.Request request = ...
MapDataPrefetcher.getInstance( ).cancelRequest(request.requestId);
...

MapDataPrefetcher operations are performed asynchronously. When available, the results of these operations are passed on to MapDataPrefetcher’s listeners. Listeners must implement the MapDataPrefetcher.Listener interface to receive notifications while fetches are progressing. Below is a code snippet on adding a listener to the MapDataPrefetcher:

MapDataPrefetcher.Listener mapDataPrefetcherListener = new MapDataPrefetcher.Listener( ) {
  public void onProgress(final int requestId, final float progress) {
  }
  public void onStatus(final int requestId, final PrefetchStatus status) {
  }
  public void onCachePurged(final boolean success) {
  }
  public void onDataSizeEstimated(final int requestId, final Boolean success, final long dataSizeKB) {
  }
};
MapDataPrefetcher.getInstance( ).addListener(mapDataPrefetcherListener);
Note: We provide MapDataPrefetcher.Adapter so you do not need to implement every method in MapDataPrefetcher.Listener.

MapDataPrefetcher.Listener.PrefetchStatus Enum

MapDataPrefetcher.Listener.PrefetchStatus is an enum data type, representing the status of MapDataPrefetcher fetch operations. The status is returned through the MapDataPrefetcher.Listener interface.

  • PREFETCH_IN_PROGRESS - Fetch operation is still in progress.
  • PREFETCH_SUCCESS - Fetch completed successfully.
  • PREFETCH_FAILURE - Fetch operation had failed to complete.
  • PREFETCH_CANCELLED - Fetch operation was cancelled.

MapDataPrefetcher.Request.Error Enum

MapDataPrefetcher.Request.Error is an enum data type, representing any errors encountered when initiating a MapDataPrefetcher fetch operation.

  • NONE – No errors in dispatching the request.
  • UNKNOWN – An unknown error has occurred during request submission.
  • BUSY – The number of requests is at max capacity.
  • INVALID_PARAMETERS – The request was invalid due to invalid parameters.
  • OPERATION_NOT_ALLOWED – ODML prefetching permission is missing.

Check the network connectivity at the application level to ensure MapDataPrefetcher operations are only performed when the device has a connection.

MapDataPrefetcher.Request

MapDataPrefetcher.Request is an object that is returned when a map data fetch is dispatched. It holds the ID of the request and a MapDataPrefetcher.Request.Error to indicate any errors that occurred.

Incremental Updates

Map data downloaded by specifying a bounding box or a route can be updated to the latest version using MapLoader APIs. Map data version is consistent for all map data across the entire system, whether the map data is downloaded or not. It is not possible to have some data from one map version and some from another version simutaneously in the cache. Therefore, it is important to keep the map version of the system up to date.

You can perform incremental updates if you are updating to the latest map data release from the two previous releases. Incremental updates are typically small downloads, as only the changes are downloaded. For example, when updating to the Q1 2018 map data release from the Q4 2017 or Q3 2017 release, an incremental update or patch is used. Where a patch is not available (such as updating from Q2 2017 to Q1 2018), using the MapLoader APIs to update to the latest version results in the removal of all downloaded map data, whether the data was downloaded on-demand or by specifying a bounding box/route.

Data Groups

Map packages are made up of several groups, each of which contains a different type of map data. Some of these groups may be selected or deselected before map packages are downloaded for offline use, depending on the needs of the application. The optional data groups are given in the SelectableDataGroup enum. To select or deselect a data group for download, pass the appropriate enum value to the MapLoader.selectDataGroup(SelectableDataGroup) or deselectDataGroup(SelectableDataGroup) method.