14.2. NextGIS Android SDK

14.2.1. Intro

NextGIS Android SDK is a set of libraries used to support work with geodata in mobile applications for Android OS. The SDK includes:

nextgis_datastore library
android_maplib library

The nextgis_datastore library is written in С++11 and based on GDAL. The library supports the following functionality:

create, modify and delete geodata (raster and vector)
edit vector geodata (modify geometry and attributes)
geodata management (copy, move, various formats import/export, etc.)
geodata rendering as maps using OpenGL/OpenGL ES
utility functions (network requests, oAuth2, json)
nextgis.com/NextGIS Web integration (under development)

The library has С API and bindings to android java/kotlin programming languages using jni.

android_maplib library is written on Kotlin and acts as easy wrapper around C API nextgis_datastore.

14.2.2. Install

To use SDK the Android Studio required. You need to add SDK to your project.

14.2.3. Add to project

To add NextGIS Mobile SDK to your project follow these steps:

Launch Android Studio.
Open you application build.gradle file.
Make sure that the parameter minSdkVersion has API level 14 or higher.
Add following line to dependency block:

dependencies {
  implementation 'com.nextgis.maplib:maplib:3.0.+'
}

14.2.4. Add map

You need to add map into your application:

As soon as possible initialize the library:

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)

    API.init(this@MainActivity)
}

Add MapView into the application layout:

<com.nextgis.maplib.MapView
     android:id="@+id/mapView"
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
     app:layout_constraintBottom_toBottomOf="parent"
     app:layout_constraintLeft_toLeftOf="parent"
     app:layout_constraintRight_toRightOf="parent"
     app:layout_constraintTop_toTopOf="parent" />

Create or open map document file:
```
val map = API.getMap("main")
```

Link map with view and enable rendering (rendering is frozen by default):

val mapView = findViewById<MapView>(R.id.mapView)
if(mapView != null) {
    mapView.setMap(map)
}
mapView.freeze = false

14.2.5. Create feature class

To create feature class in datastore follow these steps:

Get or create datastore. You can select any name for a datastore (i.e., store).
```
val dataStore = API.getStore("store")
```

Create feature class in a datastore with needed definitions.

val options = mapOf(
  "CREATE_OVERVIEWS" to "ON",
  "ZOOM_LEVELS" to "2,3,4,5,6,7,8,9,10,11,12,13,14"
)

val fields = listOf(
  Field("long", "long", Field.Type.REAL),
  Field("lat", "lat", Field.Type.REAL),
  Field("datetime", "datetime", Field.Type.DATE, "CURRENT_TIMESTAMP"),
  Field("name", "name", Field.Type.STRING)
)

val pointsFC = dataStore.createFeatureClass("points", Geometry.Type.POINT, fields, options)

Load spatial data to the feature class.

// create coordinates list
data class PtCoord(val name: String, val x: Double, val y: Double)
val coordinates = listOf(
  PtCoord("Moscow", 37.616667, 55.75),
  PtCoord("London", -0.1275, 51.507222),
  PtCoord("Washington", -77.016389, 38.904722),
  PtCoord("Beijing", 116.383333, 39.916667)
)

// Project from EPSG:4326 to EPSG:3857
val coordTransform = CoordinateTransformation.new(4326, 3857)

for(coordinate in coordinates) {
  val feature = pointsFC.createFeature()
  if(feature != null) {
    val geom = feature.createGeometry() as? GeoPoint
    if(geom != null) {
      val point = Point(coordinate.x, coordinate.y)
      val transformPoint = coordTransform.transform(point)
      geom.setCoordinates(transformPoint)
      feature.geometry = geom
      feature.setField(0, coordinate.x)
      feature.setField(1, coordinate.y)
      feature.setField(3, coordinate.name)
      pointsFC.insertFeature(feature)
    }
  }
}

14.2.6. Load feature class to datastore

To load feature class from GIS file format to datastore follow these steps:

Get or create datastore. You can select any name for a datastore (i.e., store).
```
val dataStore = API.getStore("store")
```

From catalog get a feature class object if GIS file format and copy it to the datastore.

val tmpDir = API.getTmpDirectory()
val testGeojsonObj = tmpDir?.child("test.geojson")
val copyOptions = mapOf(
  "CREATE_OVERVIEWS" to "ON",
  "NEW_NAME" to "trees"
)

val createResult = testGeojsonObj?.copy(Object.Type.FC_GPKG, store!!, true, copyOptions) ?: false
val treesFC = Object.forceChildToFeatureClass(store?.child("trees")!!)

14.2.7. Create raster

To create raster set following settings:

raster extent
name
XYZ source URL
minimum and maximum zoom levels

raster spatial reference in EPSG code

val bbox = Envelope(-20037508.34, 20037508.34, -20037508.34, 20037508.34)
val baseMap = dataDir.createTMS("osm.wconn", "http://tile.openstreetmap.org/{z}/{x}/{y}.png",
              3857, 0, 18, bbox, bbox, 14)

14.2.8. Add layer to a map with style

To add new layer to the map you need:

Add vector layer to a map

val pointsLayer = map.addLayer("Points", pointsFC)

Set style name
```
pointsLayer.styleName = "pointsLayer"
```

Setup style

val style = pointsLayer.style
style.setString("color", colorToHexString(Color.rgb(0, 190,120)))
style.setDouble("size", 8.0)
style.setInteger("type", 6) // Star symbol

Apply modified style to the layer
```
pointsLayer.style = style
```

14.2.9. SDK API References

The SDK API can be found in documentation.

14.2.10. Demo projects

See demo projects at this page.