我正在将我的应用程序连接到传感器，每次传感器发送数据时，标记都放在信息窗口内的数据的地图上。
当我第一次开始活动时。 mMap的ID：21319。在我的onLocationChanged()method中，我使用ID 21319向地图添加标记。然后，如果我按下后退按钮并恢复活动。 mMap再次创建并且现在有另一个ID，让我们说ID 22431.用我的方法addMapPoints()我将旧标记添加到ID为22431的mMap和mMap.addMarker(markerOptions)，我可以在屏幕上看到标记。但是这次发送新数据并在onLocationChanged()中添加标记时，屏幕上不会出现新标记。当我调试我可以看到在onLocationChanged()我的mMap有旧ID：21319我没有得到任何错误。所以我想新标记会添加到旧地图中，但我的屏幕会显示新地图。
为什么会这样？我该如何解决这个问题？
更新我想我找到了问题。目前mMap == null发送新数据时。我现在想知道的是如何在OnLocationUpdate()或OnResume()中获取地图？
这是我的MapsActivity代码
public class MapsActivity extends FragmentActivity implements OnMapReadyCallback, GoogleApiClient.ConnectionCallbacks, GoogleApiClient.OnConnectionFailedListener, LocationListener
{
public GoogleMap mMap;
GoogleApiClient mGoogleApiClient;
Location mLastLocation;
Marker mCurrLocationMarker;
private int co_mV;
private int no2_mV;
LocationRequest mLocationRequest;
private boolean initiateApp;
String currentTime;
TcpClient mTcpClient;
ArrayList<Marker> markerArrayList;
static ArrayList<Double> markerLat = new ArrayList<>();
static ArrayList<Double> markerLng = new ArrayList<>();
static ArrayList<String> markerSnippet = new ArrayList<>();
static ArrayList<String> markerTitle = new ArrayList<>();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_maps);
if (android.os.Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
checkLocationPermission();
}
// Obtain the SupportMapFragment and get notified when the map is ready to be used.
SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
.findFragmentById(R.id.map);
mapFragment.getMapAsync(this);
initiateApp = true;
markerArrayList = new ArrayList<>();
}
@Override
protected void onResume() {
super.onResume();
}
@Override
protected void onPause() {
super.onPause();
markerArrayList.clear();
}
/**
* Manipulates the map once available.
* This callback is triggered when the map is ready to be used.
* This is where we can add markers or lines, add listeners or move the camera. In this case,
* we just add a marker near Sydney, Australia.
* If Google Play services is not installed on the device, the user will be prompted to install
* it inside the SupportMapFragment. This method will only be triggered once the user has
* installed Google Play services and returned to the app.
*/
@Override
public void onMapReady(GoogleMap googleMap) {
mMap = googleMap;
mMap.setMapType(GoogleMap.MAP_TYPE_HYBRID);
mMap.setMyLocationEnabled(true);
//Initialize Google Play Services
if (android.os.Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
if (ContextCompat.checkSelfPermission(this,
Manifest.permission.ACCESS_FINE_LOCATION)
== PackageManager.PERMISSION_GRANTED) {
buildGoogleApiClient();
}
}
else {
buildGoogleApiClient();
}
if (markerLat != null) {
addMapPoints();
}
}
/* Here we create the infoWindow **/
protected synchronized void buildGoogleApiClient() {
mGoogleApiClient = new GoogleApiClient.Builder(this)
.addConnectionCallbacks(this)
.addOnConnectionFailedListener(this)
.addApi(LocationServices.API)
.build();
mGoogleApiClient.connect();
}
@Override
public void onConnected(Bundle bundle) {
getNewLocation();
new ConnectTask().execute("");
}
public void newData(JSONObject d) {
try {
co_mV = d.getInt("co_mV");
no2_mV = d.getInt("no2_mV");
} catch (JSONException e) {
e.printStackTrace();
}
getNewLocation();
}
public void getTime() {
Calendar cal = Calendar.getInstance();
currentTime = new SimpleDateFormat("HH:mm:ss").format(cal.getTime());
}
public void getNewLocation() {
mLocationRequest = new LocationRequest();
mLocationRequest.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY);
if (ContextCompat.checkSelfPermission(this,
Manifest.permission.ACCESS_FINE_LOCATION)
== PackageManager.PERMISSION_GRANTED) {
LocationServices.FusedLocationApi.requestLocationUpdates(mGoogleApiClient, mLocationRequest, this);
}
}
public void addMapPoints() {
markerArrayList = new ArrayList<>();
for (int i = 0; i < markerLat.size(); i++) {
LatLng latLng = new LatLng(markerLat.get(i), markerLng.get(i));
MarkerOptions markerOptions = new MarkerOptions();
markerOptions.position(latLng);
markerOptions.title(markerTitle.get(i));
markerOptions.snippet(markerSnippet.get(i));
markerOptions.icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_MAGENTA));
Marker marker = mMap.addMarker(markerOptions);
markerArrayList.add(marker);
}
}
@Override
public void onConnectionSuspended(int i) {
}
@Override
public void onLocationChanged(Location location) {
if (markerArrayList.size()>1) {
if(location.distanceTo(mLastLocation) < 30) {
markerArrayList.get(markerArrayList.size()-1).remove();
markerArrayList.remove(markerArrayList.size()-1);
markerSnippet.remove(markerSnippet.size()-1);
markerTitle.remove(markerTitle.size()-1);
markerLat.remove(markerTitle.size()-1);
markerLng.remove(markerTitle.size()-1);
Toast.makeText(
getApplicationContext(),
"Reading to close to last reading, replaces last reading", Toast.LENGTH_SHORT).show();
}
}
if (markerArrayList.size() == 8) {
markerArrayList.get(0).remove();
markerArrayList.remove(0);
markerSnippet.remove(0);
markerTitle.remove(0);
markerLat.remove(0);
markerLng.remove(0);
}
//Place current location marker
LatLng latLng = new LatLng(location.getLatitude(), location.getLongitude());
if (co_mV != 0) {
MarkerOptions markerOptions = new MarkerOptions();
markerOptions.position(latLng);
markerLat.add(location.getLatitude());
markerLng.add(location.getLongitude());
markerOptions.title("Time of reading: " + currentTime);
markerTitle.add("Time of reading: " + currentTime);
markerOptions.snippet("co: " + String.valueOf(co_mV) + " mV, " + "no2: " + String.valueOf(no2_mV) + " mV");
markerSnippet.add("co: " + String.valueOf(co_mV) + " mV, " + "no2: " + String.valueOf(no2_mV) + " mV");
markerOptions.icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_MAGENTA));
mCurrLocationMarker = mMap.addMarker(markerOptions);
markerArrayList.add(mCurrLocationMarker);
}
mLastLocation = location;
Log.d("ADebugTag", "Value: " + Double.toString(location.getLatitude()));
Log.d("ADebugTag", "Value: " + Double.toString(location.getLongitude()));
//move map camera
if(initiateApp){
mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(latLng, 15));
}
boolean contains = mMap.getProjection()
.getVisibleRegion()
.latLngBounds
.contains(latLng);
if(!contains){
mMap.moveCamera(CameraUpdateFactory.newLatLng(latLng));
}
initiateApp = false;
}
@Override
public void onConnectionFailed(ConnectionResult connectionResult) {
}
public static final int MY_PERMISSIONS_REQUEST_LOCATION = 99;
public boolean checkLocationPermission() {
if (ContextCompat.checkSelfPermission(this,
Manifest.permission.ACCESS_FINE_LOCATION)
!= PackageManager.PERMISSION_GRANTED) {
// Asking user if explanation is needed
if (ActivityCompat.shouldShowRequestPermissionRationale(this,
Manifest.permission.ACCESS_FINE_LOCATION)) {
// Show an explanation to the user *asynchronously* -- don't block
// this thread waiting for the user's response! After the user
// sees the explanation, try again to request the permission.
//Prompt the user once explanation has been shown
ActivityCompat.requestPermissions(this,
new String[]{Manifest.permission.ACCESS_FINE_LOCATION},
MY_PERMISSIONS_REQUEST_LOCATION);
} else {
// No explanation needed, we can request the permission.
ActivityCompat.requestPermissions(this,
new String[]{Manifest.permission.ACCESS_FINE_LOCATION},
MY_PERMISSIONS_REQUEST_LOCATION);
}
return false;
} else {
return true;
}
}
@Override
public void onRequestPermissionsResult(int requestCode,
String permissions[], int[] grantResults) {
switch (requestCode) {
case MY_PERMISSIONS_REQUEST_LOCATION: {
// If request is cancelled, the result arrays are empty.
if (grantResults.length > 0
&& grantResults[0] == PackageManager.PERMISSION_GRANTED) {
// permission was granted. Do the
// contacts-related task you need to do.
if (ContextCompat.checkSelfPermission(this,
Manifest.permission.ACCESS_FINE_LOCATION)
== PackageManager.PERMISSION_GRANTED) {
if (mGoogleApiClient == null) {
buildGoogleApiClient();
}
mMap.setMyLocationEnabled(true);
}
} else {
// Permission denied, Disable the functionality that depends on this permission.
Toast.makeText(this, "permission denied", Toast.LENGTH_LONG).show();
}
return;
}
// other 'case' lines to check for other permissions this app might request.
// You can add here other case statements according to your requirement.
}
}
public JSONObject getNewJSON(JSONObject json) {
try {
int humidity = json.getInt("humidity_ppm");
int pressure = json.getInt("pressure_Pa");
int noise = json.getInt("noise_dB");
double lat = mLastLocation.getLatitude();
double lng = mLastLocation.getLongitude();
long time = System.currentTimeMillis() / 1000L;
JSONObject c = new JSONObject();
c.put("time",time);
c.put("lat",lat);
c.put("long",lng);
c.put("humidity",humidity);
c.put("pressure",pressure);
c.put("noise_dB",noise);
return c;
} catch (JSONException e) {
e.printStackTrace();
}
我通过在onDestroy方法中退出应用程序来解决这个问题。我认为当片段被重用时，标记不能放在地图中
@Override
public void onDestroy() {
getActivity().finish();
System.exit(0);
super.onDestroy();
}