java - 地图片段在从其他活动返回时重新创建
问题描述
我正在尝试构建一个使用地图的应用程序，我在该地图上将一些标记固定到保存其坐标的范围内。当我单击标记时，我会保存有关这些坐标的一些详细信息，然后返回地图以添加其他坐标。问题是当我返回时，地图会重新创建删除保存的标记。我已经尝试了许多与该主题相关的解决方案，但是当我按下返回按钮时，应用程序崩溃了。你能帮我解决保存标记和片段状态的方法吗？
编辑：即使使用其他解决方案来保存我尝试过的状态并且绝对是茶线 32，应用程序也会崩溃，这不是问题所在。
地图活动：
@Override
public void onMapReady(GoogleMap googleMap) {
// Toast.makeText(this, "Map is Ready", Toast.LENGTH_SHORT).show();
Log.d(TAG, "onMapReady: map is ready");
mMap = googleMap;
mMap.setOnMarkerDragListener(this);
mMap.setOnMapLongClickListener(this);
if (mLocationPermissionsGranted) {
getDeviceLocation();
if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION)
!= PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this,
Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
return;
}
mMap.setMyLocationEnabled(true);
mMap.getUiSettings().setMyLocationButtonEnabled(false);
}
}
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_maps);
getLocationPermission();
initMap();
if(savedInstanceState != null) {
CameraPosition savedCameraPosition = savedInstanceState.getParcelable("camera");
if (savedCameraPosition != null) {
mMap.animateCamera(CameraUpdateFactory.newCameraPosition(savedCameraPosition));
}
}
}
private void getDeviceLocation() {
Log.d(TAG, "getDeviceLocation: getting the devices current location");
mFusedLocationProviderClient = LocationServices.getFusedLocationProviderClient(this);
try {
if (mLocationPermissionsGranted) {
final Task location = mFusedLocationProviderClient.getLastLocation();
location.addOnCompleteListener(new OnCompleteListener() {
@Override
public void onComplete(@NonNull Task task) {
if (task.isSuccessful()) {
Log.d(TAG, "onComplete: found location!");
Location currentLocation = (Location) task.getResult();
moveCamera(new LatLng(currentLocation.getLatitude(), currentLocation.getLongitude()),
DEFAULT_ZOOM);
} else {
Log.d(TAG, "onComplete: current location is null");
Toast.makeText(MapsActivity.this, "unable to get current location", Toast.LENGTH_SHORT).show();
}
}
});
}
} catch (SecurityException e) {
Log.e(TAG, "getDeviceLocation: SecurityException: " + e.getMessage());
}
}
private void moveCamera(LatLng latLng, float zoom) {
Log.d(TAG, "moveCamera: moving the camera to: lat: " + latLng.latitude + ", lng: " + latLng.longitude);
mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(latLng, zoom));
}
public void onMapLongClick(LatLng latLng) {
mMap.clear();
MarkerOptions markerOptions = new MarkerOptions().position(latLng).title(latLng.toString());
markerOptions.draggable(true);
mMap.addMarker(markerOptions);
mMap.setOnMarkerClickListener(this);
latlngNew = latLng;
LatLng latlngNew;
}
private void initMap() {
Log.d(TAG, "initMap: initializing map");
SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map);
mapFragment.getMapAsync(MapsActivity.this);
}
@Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
if (mMap != null) {
outState.putParcelable("camera", mMap.getCameraPosition());
}
}
private void getLocationPermission() {
Log.d(TAG, "getLocationPermission: getting location permissions");
String[] permissions = {Manifest.permission.ACCESS_FINE_LOCATION,
Manifest.permission.ACCESS_COARSE_LOCATION};
if (ContextCompat.checkSelfPermission(this.getApplicationContext(),
FINE_LOCATION) == PackageManager.PERMISSION_GRANTED) {
if (ContextCompat.checkSelfPermission(this.getApplicationContext(),
COURSE_LOCATION) == PackageManager.PERMISSION_GRANTED) {
mLocationPermissionsGranted = true;
initMap();
} else {
ActivityCompat.requestPermissions(this,
permissions,
LOCATION_PERMISSION_REQUEST_CODE);
}
} else {
ActivityCompat.requestPermissions(this,
permissions,
LOCATION_PERMISSION_REQUEST_CODE);
}
}
@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
Log.d(TAG, "onRequestPermissionsResult: called.");
mLocationPermissionsGranted = false;
switch (requestCode) {
case LOCATION_PERMISSION_REQUEST_CODE: {
if (grantResults.length > 0) {
for (int i = 0; i < grantResults.length; i++) {
if (grantResults[i] != PackageManager.PERMISSION_GRANTED) {
mLocationPermissionsGranted = false;
Log.d(TAG, "onRequestPermissionsResult: permission failed");
return;
}
}
Log.d(TAG, "onRequestPermissionsResult: permission granted");
mLocationPermissionsGranted = true;
//initialize our map
initMap();
}
}
}
}
public void changetype(View view) {
if (mMap.getMapType() == GoogleMap.MAP_TYPE_NORMAL) {
mMap.setMapType(MAP_TYPE_SATELLITE);
} else
mMap.setMapType(GoogleMap.MAP_TYPE_NORMAL);
}
@Override
public void onMarkerDragStart(Marker marker) {
marker.setTitle(marker.getPosition().toString());
marker.showInfoWindow();
marker.setAlpha(0.5f);
}
@Override
public void onMarkerDrag(Marker marker) {
marker.setTitle(marker.getPosition().toString());
marker.showInfoWindow();
marker.setAlpha(0.5f);
}
@Override
public void onMarkerDragEnd(Marker marker) {
marker.setTitle(marker.getPosition().toString());
marker.showInfoWindow();
marker.setAlpha(1.0f);
}
@Override
public boolean onMarkerClick(Marker marker) {
openDialog();
return false;
}
public void openDialog() {
final Dialog dialog = new Dialog(this);
dialog.setContentView(R.layout.dialog);
dialog.setTitle(R.string.default_info_title);
dialog.show();
Button bt_da = (Button)dialog.findViewById(R.id.dialog_ok);
Button bt_nu = (Button)dialog.findViewById(R.id.dialog_cancel);
bt_da.setOnClickListener(this);
bt_nu.setOnClickListener(this);
bt_nu.setOnClickListener(new View.OnClickListener()
{
@Override
public void onClick(View v) {
dialog.dismiss();
}
}
);
bt_da.setOnClickListener(new View.OnClickListener()
{
@Override
public void onClick(View v) {
Intent intent=new Intent(MapsActivity.this,MainActivity.class);
intent.putExtra("markerLat", latlngNew.latitude);
intent.putExtra("markerLong", latlngNew.longitude);
startActivity(intent);
}
}
);
}
@Override
public void onClick(View v) {
}
@Override
public void onMapClick(LatLng latLng) {
}
@Override
public void onCameraMove() {
}
以及按 Return 时的错误：
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.google.android.gms.maps.c.b(com.google.android.gms.maps.a)' on a null object reference
at com.example.raluca.geoloc.feature.MapsActivity.onCreate(Unknown Source:32)
at android.app.Activity.performCreate(Activity.java:6975)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1214)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2775)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2897)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1598)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:251)
at android.app.ActivityThread.main(ActivityThread.java:6572)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
在第 32 行有这个：
import static com.google.android.gms.maps.GoogleMap.MAP_TYPE_SATELLITE;
解决方案
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