Efficient Way To Get JSON Data To Wearable

Question

I am attempting to read a feed from a URL in the form of a JSON Object, and pass that feed to a Wearable device to display as a list using the Data API. This JSON Object contains an array of objects, each object containing a few elements. Something like this:

{ "items":[
    { "title":"item 1", "element_1":"element 1", "element_2":"element 2" }
    { "title":"item 2", "element_1":"element 1", "element_2":"element 2" }
    { "title":"item 3", "element_1":"element 1", "element_2":"element 2" }
]}

I can get these items into an ArrayList of objects using GSON, or Jackson (though I think I prefer GSON), but I do not know how I would be able to that ArrayList of objects to the wearable. From what I can tell, I cannot. I would like to know if there is a way to do this, or if not, some sort of best practices on how I should go about this? Should I just get the JSON as a string, pass the string to the wearable, and parse it afterwards? I do not know if this would be inefficient if the string were very large though, considering I do not know how large the list of JSON objects could get. Also I know it is possible to parse a string with GSON, but I do not know if this is inefficient as well.

Answer 1

I found the Android Wear Sample XYZTouristAttractions, and this is my current code based on that example. Firstly, I created a shared library to reduce duplicate code. This shared library contains the Item class that holds the JSON data. I use this class in my DownloadArrayListTask on the handheld, which takes the JSON Object from the input stream and puts the data in an ArrayList of Item objects.

@Override
protected ArrayList<Item> doInBackground(URL... params) {
    URL url = params[0];
    ArrayList<Item> items = new ArrayList<>();

    try {
        HttpURLConnection connection = (HttpURLConnection) url.openConnection();
        try {
            InputStreamReader input = new InputStreamReader(connection.getInputStream());

            Type listType = new TypeToken<Map<String, ArrayList<Item>>>(){}.getType();
            Gson gson = new GsonBuilder().create();
            Map<String, ArrayList<Item>> treeMap = gson.fromJson(input, listType);
            items = treeeMap.get("items");

            input.close();
        } finally {
            connection.disconnect();
        }
    } catch (IOException exception) {
        exception.printStackTrace();
    }

    return items
}

This ArrayList is broken apart into strings in the DataLayerListenerService and placed in an ArrayList of DataMap objects for the wearable to receive.

@Override
public void onMessageReceived(MessageEvent messageEvent) {
    GoogleApiClient googleApiClient = new GoogleApiClient.Builder(this)
            .addApi(Wearable.API).build();

    ConnectionResult connectionResult = googleApiClient.blockingConnect(30, TimeUnit.SECONDS);
    if(!connectionResult.isSuccess()) {
        Log.e(TAG, "Failed to connect to Google API Client");
        return;
    }

    if(messageEvent.getPath().equals("/update_path") {
        ArrayList<Item> items = new ArrayList<>()
        try {
            items = new DownloadArrayListTask().execute(new URL("http://my_url")).get();
        } catch (MalformedURLException | InterruptedException | ExecutionException exception) {
            exception.printStackTrace();
        }

        ArrayList<DataMap> itemMaps = new ArrayList<>(items.size());

        for(Item item : items) {
            DataMap dataMap = new DataMap();
            dataMap.putString("title", item.getTitle());
            dataMap.putString("element1", item.getElement1());
            dataMap.putString("element2", item.getElement2());

            itemMaps.add(dataMap);
        }

        new Thread(new Runnable() {
            @Override
            public void run() {
                NodeApi.GetConnectedNodesResult nodes = Wearable.NodeApi.getConnectedNodes(googleApiClient).await();

                for(Node node : nodes.getNodes()) {
                    PutDataMapRequest dataMapRequest = PutDataMapRequest.create("/item_path");
                    dataMapRequest.getDataMap().putDataMapArrayList("item_key", itemMaps);

                    PutDataRequest request = dataMapRequest.asPutDataRequest();
                    DataApi.DataItemResult result = Wearable.DataApi.putDataItem(googleApiClient, request).await();

                    if(!result.getStatus().isSuccess()) {
                        Log.d(TAG, "Failed to send data");
                    }
                } 
            }
        }).start();
    }
}

Then the wearable device receives this ArrayList of DataMap objects, and uses its own AsyncTask to put them back into an ArrayList of Item objects.

@Override
protected ArrayList<Item> doInBackground(Uri... params) {
    Uri uri = params[0];
    ArrayList<Item> items = new ArrayList<>();

    GoogleApiClient googleApiClient = new GoogleApiClient.Builder(this)
            .addApi(Wearable.API).build();

    ConnectionResult connectionResult = googleApiClient.blockingConnect(30, TimeUnit.SECONDS);
    if(!connectionResult.isSuccess()) {
        Log.e(TAG, "Failed to connect to Google API Client");
        return;
    }

    DataItemBuffer results = Wearable.DataApi.getDataItems(googleApiClient).await();

    if(results.getStatus().isSuccess() && results.getCount() != 0) {
        DataMapItem dataMapItem = DataMapItem.fromDataItem(results.get(0);

        List<DataMap> data = dataMapItem.getDataMap().getDataMapArrayList("item_key");

        for(DataMap dataItem : data) {
            Item item = new Item(dataItem.getString("title"),
                    dataItem.getString("element1"),
                    dataItem.getString("element2"));
            items.add(item);
        }
    } else {
        Log.d(TAG, "Failed to obtain data");
    } return items;
}