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androidhere-api

Are there any thread restrictions on performing operations on the Here SDK Map object?

The way I understand the HERE Android SDK is that there's a MapView that has a backing Map object. Adding objects, setting the center, zooming etc should be performed on the Map object and this eventually reflects on the MapView.

Question:

Are there any restrictions on what thread the operations on the Map object must be performed? For example, must they all be called on the UI thread? Also, should multiple subsequent calls be synchronized?

I ask this because I want to make multiple changes in a Map (resize the map view, change some visible layers, change the scheme, add a MapRoute and zoom out to the bounding box of the route). When I try this, it sometimes works but sometimes doesn't. Sometimes, only some of the operations are applied. For example, everything works except the zoom is not applied.

I know there are some listeners that can help me:

  1. Map.OnTransformListener - this I can use to let me know when a zooming operation has ended
  2. Map.OnSchemeChangedListener - this I can use to know when a scheme change event has ended

What is not clear to me from the documentation is what other operations constitute a "transform"? Which of these operations must be performed in a synchronized fashion?

For example, is the following code expected to behave correctly?

map.setCenter(coordinate, Animation.BOW, 18, 0f, 60f);
map.addMapObject(routeObject);
map.setVisibleLayers(layersToShow, true);
map.setScheme(Map.Scheme.NORMAL_DAY)

Note that in the above example, I'm proceeding to make changes immediately after setCenter even before the animation is complete. Is this the expected way to use the API?

Solution

  • There is no restriction on what thread you call the API from. Internally, all calls are synchronized and thread safe.

    What you are looking for is the MapView#executeSynchronized API. [link] This will batch up a few operations into one screen redraw. [At least when I wrote that API a few years ago]

    What you are experiencing happens because the underlying rendering thread started drawing some of the commands from the calling thread. This caused subsequent calls to lose effect.