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Join local JSON data with vector tile geometries

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This page uses v9.7.1 of the Mapbox Maps SDK. A newer version of the SDK is available. Learn about the latest version, v11.7.0, in the Maps SDK documentation.
Note

This example is a part of the Mapbox Android Demo app. You can find the values for all referenced resources in the res directory. For example, see res/values/activity_strings.xml for R.string.* references used in this example. The dependencies can be found here.The examples use View binding.See setup documention if necessary.

activity_choropleth_json_vector_mix
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:mapbox="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.mapbox.mapboxandroiddemo.examples.dds.ChoroplethJsonVectorMixActivity">

<com.mapbox.mapboxsdk.maps.MapView
android:id="@+id/mapView"
android:layout_width="match_parent"
android:layout_height="match_parent"
mapbox:mapbox_cameraTargetLat="38.00312"
mapbox:mapbox_cameraTargetLng="-98.398423"
mapbox:mapbox_cameraZoom="1"/>

</FrameLayout>
ChoroplethJsonVectorMixActivity.java
package com.mapbox.mapboxandroiddemo.examples.dds;

import android.os.AsyncTask;
import android.os.Bundle;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;

import com.mapbox.mapboxandroiddemo.R;
import com.mapbox.mapboxsdk.Mapbox;
import com.mapbox.mapboxsdk.maps.MapView;
import com.mapbox.mapboxsdk.maps.MapboxMap;
import com.mapbox.mapboxsdk.maps.OnMapReadyCallback;
import com.mapbox.mapboxsdk.maps.Style;
import com.mapbox.mapboxsdk.style.expressions.Expression;
import com.mapbox.mapboxsdk.style.layers.FillLayer;
import com.mapbox.mapboxsdk.style.sources.VectorSource;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.io.InputStream;
import java.lang.ref.WeakReference;
import java.util.Scanner;

import timber.log.Timber;

import static com.mapbox.mapboxsdk.style.expressions.Expression.get;
import static com.mapbox.mapboxsdk.style.expressions.Expression.match;
import static com.mapbox.mapboxsdk.style.expressions.Expression.rgba;
import static com.mapbox.mapboxsdk.style.expressions.Expression.stop;
import static com.mapbox.mapboxsdk.style.expressions.Expression.toNumber;
import static com.mapbox.mapboxsdk.style.layers.PropertyFactory.fillColor;

/**
* Style a choropleth map by merging local JSON data with vector tile geometries
*/
public class ChoroplethJsonVectorMixActivity extends AppCompatActivity implements OnMapReadyCallback {

private static final String STATE_UNEMPLOYMENT_INFO_JSON_FILE = "state_unemployment_info.json";
private static final String VECTOR_SOURCE_NAME = "states";
private static final String DATA_MATCH_PROP = "STATE_ID";
private static final String DATA_STYLE_UNEMPLOYMENT_PROP = "unemployment";

private MapView mapView;
private MapboxMap mapboxMap;
private JSONArray statesArray;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);

// Mapbox access token is configured here. This needs to be called either in your application
// object or in the same activity which contains the mapview.
Mapbox.getInstance(this, getString(R.string.access_token));

// This contains the MapView in XML and needs to be called after the account manager
setContentView(R.layout.activity_choropleth_json_vector_mix);

mapView = findViewById(R.id.mapView);
mapView.onCreate(savedInstanceState);
mapView.getMapAsync(this);
}

@Override
public void onMapReady(@NonNull final MapboxMap map) {

this.mapboxMap = map;
map.setStyle(Style.LIGHT, new Style.OnStyleLoaded() {
@Override
public void onStyleLoaded(@NonNull Style style) {

// Add Mapbox-hosted vector source for state polygons
style.addSource(new VectorSource(VECTOR_SOURCE_NAME, "mapbox://mapbox.us_census_states_2015"));

new LoadJson(ChoroplethJsonVectorMixActivity.this).execute();
}
});
}

/**
* Create layer from the vector tile source with data-driven style
*
* @param stops the array of stops to use in the FillLayer
*/
private void addDataToMap(@NonNull Expression.Stop[] stops) {

FillLayer statesJoinLayer = new FillLayer("states-join", VECTOR_SOURCE_NAME);
statesJoinLayer.setSourceLayer(VECTOR_SOURCE_NAME);
statesJoinLayer.withProperties(
fillColor(match(toNumber(get(DATA_MATCH_PROP)),
rgba(0, 0, 0, 1), stops))
);

// Add layer to map below the "waterway-label" layer
if (mapboxMap != null) {
mapboxMap.getStyle(style -> style.addLayerAbove(statesJoinLayer, "waterway-label"));
}
}

private static class LoadJson extends AsyncTask<Void, Void, Expression.Stop[]> {

private WeakReference<ChoroplethJsonVectorMixActivity> weakReference;
private static final String TAG = "ChJSonVectorMix";

LoadJson(ChoroplethJsonVectorMixActivity activity) {
this.weakReference = new WeakReference<>(activity);
}

@Override
protected Expression.Stop[] doInBackground(Void... voids) {
try {
ChoroplethJsonVectorMixActivity activity = weakReference.get();
if (activity != null) {

InputStream inputStream = activity.getAssets().open(STATE_UNEMPLOYMENT_INFO_JSON_FILE);

activity.statesArray = new JSONArray(convertStreamToString(inputStream));

// Create stops array
Expression.Stop[] stops = new Expression.Stop[activity.statesArray.length()];

for (int x = 0; x < activity.statesArray.length(); x++) {
try {
// Generate green color value for each state/stop
JSONObject singleState = activity.statesArray.getJSONObject(x);
double green = singleState.getDouble(DATA_STYLE_UNEMPLOYMENT_PROP) / 14 * 255;

// Add new stop to array of stops
stops[x] = stop(
Double.parseDouble(singleState.getString(DATA_MATCH_PROP)),
rgba(0, green, 0, 1)
);

} catch (JSONException exception) {
throw new RuntimeException(exception);
}
}

return stops;
}
} catch (Exception exception) {
Timber.d("Exception Loading GeoJSON: %s", exception.toString());
}
return null;
}

static String convertStreamToString(InputStream is) {
Scanner scanner = new Scanner(is).useDelimiter("\\A");
return scanner.hasNext() ? scanner.next() : "";
}

@Override
protected void onPostExecute(@Nullable Expression.Stop[] stopsArray) {
super.onPostExecute(stopsArray);
ChoroplethJsonVectorMixActivity activity = weakReference.get();
if (activity != null && stopsArray != null) {
activity.addDataToMap(stopsArray);
}
}
}

@Override
protected void onStart() {
super.onStart();
mapView.onStart();
}

@Override
public void onResume() {
super.onResume();
mapView.onResume();
}

@Override
public void onPause() {
super.onPause();
mapView.onPause();
}

@Override
protected void onStop() {
super.onStop();
mapView.onStop();
}

@Override
public void onLowMemory() {
super.onLowMemory();
mapView.onLowMemory();
}

@Override
protected void onDestroy() {
super.onDestroy();
mapView.onDestroy();
}

@Override
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
mapView.onSaveInstanceState(outState);
}
}