Kotlin：如何获取经度和纬度以故意调用Google地图？

Question

i have a code like this

//onCreate()

btnmap.setOnClickListener{
 viewMap()
}

//end of onCreate()

var MyLongitude:Double? = null
var Mylatitude:Double? = null

fun location(){
 var locationListener = object : LocationListener {
        override fun onLocationChanged(locationn: Location?) {

            Mylongitude = locationn!!.longitude //i want to take this value
            Mylatitude = locationn.latitude //i want to take this value

        }
      ....
    }
}

fun viewMap(){
    Log.i(LOG, "$MyLongitude, $Mylatitude") //the output is null, null
    val gmmIntentUri = Uri.parse("google.streetview:cbll=$MyLatitude,$MyLongitude")
    val mapIntent = Intent(Intent.ACTION_VIEW, gmmIntentUri)
    mapIntent.setPackage("com.google.android.apps.maps");
    startActivity(mapIntent)
}

i wanna call a google map with intent to know where is my location now, to do that i need a value of latitude and longitude in location(), if you see my code when i call in Log MyLatitude and MyLongitude in viewMap() the output is always null even though it has been given a value in location() before

i've try to call viewMap() inside onLocationChanged() in location() and i get the value of latitude and longitude, but that is makes my app always call google map automatically every time the location changed

normally my app will call google map when i press the button btnmap

so, how to take a value of latitude and longitude from location() function for the intent in viewMap()?

Answer 1

You can learn more about user location from here . To get current location you have to ask user permission and define it in your AndroidManifest.xml file:

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

In your Activity's onCreate() method define the following:

val permissionState = ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION)
if (permissionState != PackageManager.PERMISSION_GRANTED) {
    ActivityCompat.requestPermissions(this, arrayOf(Manifest.permission.ACCESS_COARSE_LOCATION), REQUEST_PERMISSIONS_REQUEST_CODE)
}

and override onRequestPermissionsResult function like here:

override fun onRequestPermissionsResult(requestCode: Int, permissions: Array<out String>, grantResults: IntArray) {
    when (requestCode) {
        REQUEST_PERMISSIONS_REQUEST_CODE -> {
            if (grantResults.size > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED)
                getLocation()
        }
    }
}

So, that was the main part of getting user location. For the simplicity here is full code:

class MainActivity : AppCompatActivity() {

    companion object {
        private const val REQUEST_PERMISSIONS_REQUEST_CODE = 1
    }

    private lateinit var txtView: TextView
    private lateinit var fusedLocationClient: FusedLocationProviderClient

    private var myLongitude: Double? = null
    private var myLatitude: Double? = null

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

        txtView = findViewById(R.id.txtView)
        txtView.setOnClickListener {
            viewMap()
        }

        fusedLocationClient = LocationServices.getFusedLocationProviderClient(this)

        val permissionState = ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION)
        if (permissionState != PackageManager.PERMISSION_GRANTED) {
            ActivityCompat.requestPermissions(this, arrayOf(Manifest.permission.ACCESS_COARSE_LOCATION), REQUEST_PERMISSIONS_REQUEST_CODE)
        }

        if (myLatitude == null || myLatitude == null)
            getLocation()
    }

    override fun onRequestPermissionsResult(requestCode: Int, permissions: Array<out String>, grantResults: IntArray) {
        when (requestCode) {
            REQUEST_PERMISSIONS_REQUEST_CODE -> {
                if (grantResults.size > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED)
                    getLocation()
            }
        }
    }

    private fun viewMap() {
        Log.i("LOG", "$myLongitude, $myLatitude")

        val gmmIntentUri = Uri.parse("google.streetview:cbll=$myLatitude,$myLongitude")
        val mapIntent = Intent(Intent.ACTION_VIEW, gmmIntentUri)

        mapIntent.setPackage("com.google.android.apps.maps");
        startActivity(mapIntent)
    }

    @SuppressLint("MissingPermission")
    private fun getLocation() {
        fusedLocationClient.lastLocation.addOnSuccessListener { location : Location? ->
            location?.let {
                myLongitude = it.longitude
                myLatitude = it.latitude
            }
        }
    }
}

For more detailed information about user location just refer to the link above, there are a lot of learning materials.