请告诉我你对此的看法.. 我用GoogleMap片段活动（MapsActivity）和另外两个活动（MainActivity，MapsContainerActivity）创建了一个应用程序 主Activity是带有ListView的主页。基本上，ListView有一个项目，当点击..将启动一个意图转到MapsContainerActivity ..
内部MapsActivity，我有OnMapLongClick一实现中，简单地以咔嗒位置添加标记...它是完全功能性，如果我直接从在MainActivity开始MapsActivity，但是，它＆＃39; S引起一个NullPointerException当我尝试从MapsContainer Activity
访问OnMapLongClick的功能这里是MainActivity.java：
public class MainActivity extends AppCompatActivity
implements GoogleApiClient.ConnectionCallbacks, GoogleApiClient.OnConnectionFailedListener{
GoogleApiClient mGoogleApiClient;
Location mLastLocation;
//ListView stuff
ListView locationsListView;
static ArrayList<String> locationsList;
double lat = 0;
double lng = 0;
protected void onStart() {
mGoogleApiClient.connect();
super.onStart();
}
protected void onStop() {
mGoogleApiClient.disconnect();
super.onStop();
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
locationsListView = (ListView) findViewById(R.id.locationsListView);
locationsList = new ArrayList<>();
locationsList.add("Add a new place...");
ArrayAdapter arrayAdapter = new ArrayAdapter(this,android.R.layout.simple_list_item_1,locationsList);
locationsListView.setAdapter(arrayAdapter);
locationsListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
Intent intent = new Intent(getApplicationContext(),MapsContainerActivity.class);
intent.putExtra("locationInfo",position);
startActivity(intent);
}
});
// Create an instance of GoogleAPIClient.
if (mGoogleApiClient == null) {
mGoogleApiClient = new GoogleApiClient.Builder(this)
.addConnectionCallbacks(this)
.addOnConnectionFailedListener(this)
.addApi(LocationServices.API)
.build();
}
}
public void getLocation(View view){
if(lat != 0 && lng != 0){
Intent intent = new Intent(MainActivity.this,MapsActivity.class);
intent.putExtra("Latitude", lat);
intent.putExtra("Longitude", lng);
startActivity(intent);
}else {
Toast.makeText(getApplicationContext(),"Location not retrieved, try again!",Toast.LENGTH_LONG).show();
}
}
@Override
public void onConnected(Bundle connectionHint) {
mLastLocation = LocationServices.FusedLocationApi.getLastLocation(
mGoogleApiClient);
if (mLastLocation != null) {
Log.i("Latitude",mLastLocation.getLatitude()+"");
lat = mLastLocation.getLatitude();
Log.i("Longitude",mLastLocation.getLongitude()+"");
lng = mLastLocation.getLongitude();
}
}
@Override
public void onConnectionSuspended(int i) {
}
@Override
public void onConnectionFailed(@NonNull ConnectionResult connectionResult) {
}
}
这是MapsActivity.java：
public class MapsActivity extends FragmentActivity implements OnMapReadyCallback, GoogleMap.OnMapLongClickListener {
public MapsActivity(Context context){
}
Geocoder geocoder;
int selectedItem = -1;
private GoogleMap mMap;
double lat = 10;
double lng = 10;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_maps_container);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
// 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);
Intent intent = getIntent();
lat = intent.getDoubleExtra("Latitude", 0);
lng = intent.getDoubleExtra("Longitude", 0);
selectedItem = intent.getIntExtra("locationInfo", -1);
}
@Override
public void onMapReady(GoogleMap googleMap) {
mMap = googleMap;
if (selectedItem != 0 && selectedItem != -1) {
mMap.animateCamera(CameraUpdateFactory.newLatLngZoom(new LatLng(lat, lng), 8));
}
mMap.setOnMapLongClickListener(this);
// Add a marker in Sydney and move the camera
mMap.animateCamera(CameraUpdateFactory.newLatLngZoom(new LatLng(lat, lng), 8));
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
ActionBar actionBar = getActionBar();
actionBar.setDisplayHomeAsUpEnabled(true);
return super.onCreateOptionsMenu(menu);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case android.R.id.home:
this.finish();
return true;
default:
return super.onOptionsItemSelected(item);
}
}
@Override
public void onMapLongClick(LatLng point) {
geocoder = new Geocoder(getApplicationContext(), Locale.getDefault());
String label = new Date().toString();
try {
if (geocoder != null) {
List<Address> listAddresses = geocoder.getFromLocation(point.latitude, point.longitude, 1);
if (listAddresses != null && listAddresses.size() > 0) {
label = listAddresses.get(0).getAddressLine(0);
}
}
} catch (IOException e) {
e.printStackTrace();
}
if(label == null){
label = new Date().toString();
}
mMap.addMarker(new MarkerOptions()
.position(point)
.title(label)
.icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_AZURE)));
Log.i("Latitude", " " + point.latitude);
Log.i("Latitude", " " + point.longitude);
}
}
这是MapsContainerActivity：
public class MapsContainerActivity extends AppCompatActivity {
private MapsActivity mapsActivity;
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_maps_container);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
getSupportActionBar().setDisplayShowHomeEnabled(true);
mapsActivity = new MapsActivity(this);
SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
.findFragmentById(R.id.map);
mapFragment.getMapAsync(mapsActivity);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.menu_main, menu); // <--
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()){
case android.R.id.home:
this.finish();
return true;
default:
return super.onOptionsItemSelected(item);
}
}
}
顺便说一下，我创建了这个MapsContainerActivity，因为我想在MapsContainerActivity布局中包含 MapsActivity片段..所以我可以添加一个工具栏。
我尝试长按地图时遇到的错误在这里：
java.lang.NullPointerException
at android.content.ContextWrapper.getApplicationContext(ContextWrapper.java:114)
at com.firashashash.myapplication.MapsActivity.onMapLongClick(MapsActivity.java:109)
at com.google.android.gms.maps.GoogleMap$24.onMapLongClick(Unknown Source)
at com.google.android.gms.maps.internal.zzs$zza.onTransact(Unknown Source)
at android.os.Binder.transact(Binder.java:361)
at com.google.android.gms.maps.internal.bt.a(:com.google.android.gms.DynamiteModulesB:93)
at com.google.maps.api.android.lib6.gmm6.api.ac.a(:com.google.android.gms.DynamiteModulesB:468)
at com.google.maps.api.android.lib6.gmm6.vector.af.d(:com.google.android.gms.DynamiteModulesB:700)
at com.google.maps.api.android.lib6.gmm6.vector.df.onLongPress(:com.google.android.gms.DynamiteModulesB:341)
at com.google.maps.api.android.lib6.impl.gesture.g.onLongPress(:com.google.android.gms.DynamiteModulesB:179)
at com.google.maps.api.android.lib6.impl.gesture.i.handleMessage(:com.google.android.gms.DynamiteModulesB:3579)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:157)
at android.app.ActivityThread.main(ActivityThread.java:5356)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081)
at dalvik.system.NativeStart.main(Native Method)