How to download GeoJSON file in Kotlin?

Question

So the GeoJSON file will be created with the following code:

val coordinates = listOf(
Coordinate(4.5165132153, 99.651681683),
Coordinate(4.5163152153, 99.878981683),
Coordinate(4.3584532153, 99.021481683),
Coordinate(4.1578132153, 99.698781683),
Coordinate(4.3655132153, 99.321481683),
Coordinate(4.8795132153, 99.874581683)
)

val geometry = mapOf(
    "type" to "Polygon",
    "coordinates" to listOf(listOf(coordinates.map { listOf(it.lon, it.lat) }))
)

val properties = mapOf(
    "name" to "Your Polygon Name",
    // Add other properties as needed
)

val feature = mapOf(
    "type" to "Feature",
    "geometry" to geometry,
    "properties" to properties
)

val featureCollection = mapOf(
    "type" to "FeatureCollection",
    "features" to listOf(feature)
)

Then serialise the GeoJSON data into JSON string

val gson = Gson()
val geoJsonString = gson.toJson(featureCollection)

Then write the JSON string in the app's internal storage

val fileName = "my_polygon.geojson"
val file = File(context.filesDir, fileName)

file.writeText(geoJsonString)

So I would like to download this data and save it into the phone storage by clickling a button, for example: binding.downloadButton.setOnClickListener{ }

Does anyone know how to perform this task?

Thank you!

Answer 1

First, define the required permissions.

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

Check permissions.

if (checkSelfPermission(Manifest.permission.WRITE_EXTERNAL_STORAGE)
       == PackageManager.PERMISSION_DENIED) {
    requestPermissions(
        arrayOf(Manifest.permission.WRITE_EXTERNAL_STORAGE),
        PERMISSION_REQUEST_CODE
    )
}

And save file operation

try {
    val root =  Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOCUMENTS)
    if (!root.exists()) {
        root.mkDirs()
    }
    val file = File(root, "fileName.json")
    val writer = FileWriter(file)
    writer.append(geoJsonString)
    writer.flush()
    writer.close()
} catch (e: Exception) {
    e.printStackTrace()
}

Your case

binding.downloadButton.setOnClickListener {
    if (checkSelfPermission(Manifest.permission.WRITE_EXTERNAL_STORAGE)
            == PackageManager.PERMISSION_DENIED) {
        requestPermissions(
            arrayOf(Manifest.permission.WRITE_EXTERNAL_STORAGE),
            PERMISSION_REQUEST_CODE
        )
    } else {
        try {
            val root =  Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOCUMENTS)
            if (!root.exists()) {
                root.mkdirs()
            }
            val file = File(root, "fileName.json")
            val writer = FileWriter(file)
            writer.append(geoJsonString)
            writer.flush()
            writer.close()
        } catch (e: IOException) {
            e.printStackTrace()
        }
    }
}