伙计，
我正在尝试向用户发送当前纬度和经度，从MainActivity中的按钮单击发送到MapFragment（片段）。我使用fromMainActivity中实现的片段接口，但是当我尝试从Fragment onButtonClick获取方法时，我得到了一个
在android.app.ActivityThread.main（ActivityThread.java:5221） at java.lang.reflect.Method.invoke（Native Method） 在java.lang.reflect.Method.invoke（Method.java:372） 在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:899） 在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:694） 引发者：java.lang.NullPointerException：尝试在空对象引用上调用虚方法'void com.xtechkid.blah.threadingapplication.MapDemoActivity.setupCurrlocation（com.google.android.gms.maps.model.LatLng）' 在com.xtechkid.sudheej.threadingapplication.MainActivity.findLocation（MainActivity.java:67）
我的代码在
下面这是地图片段
public class MapDemoActivity extends Fragment {
final LatLng MU = new LatLng(40.8874245, 67.0200729);
private GoogleMap mMap; // Might be null if Google Play services APK is not available.
CommInter mCallback;
public interface CommInter {
public void communicatesWithActivity(double lati,double longi);
}
@Override
public void onAttach(Context context) {
super.onAttach(context);
Activity a;
// if (context instanceof Activity){
a=(Activity) context;
//}
try{
mCallback = (CommInter) a;
}catch (ClassCastException e){
throw new ClassCastException(a.toString());
}
}
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.activity_main, container, false);
//setUpMapIfNeeded();
if (mMap != null) {
mMap.setMyLocationEnabled(true);
}
return view;
}
//This method when called from Main is throwing Exception
public void setupCurrlocation(LatLng MUSEUM) {
makeText(getContext(), "I am inside the function ", Toast.LENGTH_LONG).show();
System.out.println("I am inside the function");
/*CameraPosition cameraPosition = new CameraPosition.Builder()
.target(MUSEUM)
.zoom(10)
.bearing(70)
.tilt(25)
.build();
mMap.animateCamera(CameraUpdateFactory.newCameraPosition(cameraPosition));
*/
}
}
主要活动代码
import android.app.FragmentManager;
import android.support.v7.app.AppCompatActivity;
import android.content.Intent;
import android.location.LocationManager;
import android.os.Bundle;
import android.provider.Settings;
import android.view.View;
import android.widget.TextView;
import android.widget.Toast;
import com.google.android.gms.maps.model.LatLng;
public class MainActivity extends AppCompatActivity implements MapDemoActivity.CommInter {
private TextView txtLocation;
private String provider;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
@Override
public void communicatesWithActivity(double lati, double longi) {
MapDemoActivity mapFrag = (MapDemoActivity)getSupportFragmentManager().findFragmentById(R.id.map);
final LatLng MUSEU = new LatLng(38.8874245, 77.0200729);
//final LatLng MUSEU = new LatLng(lati, longi);
mapFrag.setupCurrlocation(MUSEU);
}
public void findLocation(View v) {
//final LatLng setLoc = new LatLng(38.8874245, -77.0200729);
//// MapDemoActivity fragment;
// Fragment t = (Fragment)getSupportFragmentManager()findViewById(R.id.map);
// fragment.setupCurrlocation(v,setLoc);
txtLocation = (TextView) findViewById(R.id.textViewLocation);
LocationManager service = (LocationManager) getSystemService(LOCATION_SERVICE);
boolean isLocEnabled = service.isProviderEnabled(LocationManager.GPS_PROVIDER);
if (!isLocEnabled) {
Intent intent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);
startActivity(intent);
}
GPSTracker gps = new GPSTracker(MainActivity.this);
// check if GPS enabled
if(gps.canGetLocation()){
double latitude = gps.getLatitude();
double longitude = gps.getLongitude();
// \n is for new line
Toast.makeText(getApplicationContext(), "Your Location is - \nLat: " + latitude + "\nLong: " + longitude, Toast.LENGTH_LONG).show();
txtLocation.setText("Lat: " + latitude + "Long: " + longitude);
//System.out.println(MUS);
//The PROBLEM IS HERE I DONT KNOW THE FIX
communicatesWithActivity(latitude,long);
}else{
// can't get location
// GPS or Network is not enabled
// Ask user to enable GPS/network in settings
gps.showSettingsAlert();
}
}
}
答案 0 :(得分：2)
您没有使用谷歌地图。您需要在调用setupcurrlocation的地方进行所有这些导入。
import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.MapFragment;
import com.google.android.gms.maps.model.CameraPosition;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.Marker;
import com.google.android.gms.maps.model.MarkerOptions;
// et al...
public void setupCurrlocation(LatLng MUSEUM) {
GoogleMap googleMap = ((MapFragment) fragmentManager.
findFragmentById(R.id.map)).getMap();
googleMap.setMapType(GoogleMap.MAP_TYPE_HYBRID);
Marker marker = googleMap.addMarker(new MarkerOptions().position(latLng).title(null));
CameraPosition cameraPosition = new CameraPosition.Builder().target(MUSEUM).zoom(10).bearing(70).tilt(25)
.build();
googleMap.animateCamera(CameraUpdateFactory.newCameraPosition(cameraPosition));
}
基本上我会在片段附加到的活动中使用此方法。然后，您需要管理Google地图的可见性。因为它将保留在其他片段之上。
通过控制framelayouts的可见性，您可以控制地图在其framelayout中的可见性。
示例：
// your activity layout here:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
//TO DO/>
<RelativeLayout
android:layout_height="wrap_content"
android:layout_width="match_parent"
android:id="@+id/myrellayout">
// ALL THE THINGS IN YOUR ACTIVTY
</RelativeLayout>
// THE FRAMELAYOUTS MANAGE YOUR MAP FRAGMENT AND OTHER FRAGMENTS VISIBILITY
<FrameLayout
android:id="@+id/firstfrag"
android:layout_below="@+id/myrellayout"
android:layout_height="fill_parent"
android:layout_width="match_parent"
android:visibility="gone"/>
<FrameLayout
android:id="@+id/secondfrag"
android:layout_below="@+id/myrellayout"
android:layout_height="fill_parent"
android:layout_width="match_parent"
android:visibility="gone"/>
<fragment
android:id="@+id/map"
android:layout_height="match_parent"
android:layout_width="match_parent"
android:name="com.google.android.gms.maps.MapFragment"/>
</FrameLayout>
</RelativeLayout>
https://developers.google.com/maps/documentation/android-api/ https://developers.google.com/maps/documentation/javascript/examples/
答案 1 :(得分：2)
由于findFragmentById返回null，因此活动中发生异常。根据您发布的代码，您已在xml中声明了Fragment。由于您使用的是getSupportFragmentManager，因此请确保使用com.google.android.gms.maps.SupportMapFragment而不是com.google.android.gms.maps.MapFragment进行宣传。这可能是您获得null的原因之一。另一方面，你可以使用transactin
私有MapDemoActivity mFragment;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (savedInstanceState == null) {
mFragment = new MapDemoActivity();
getSupportFragmentManager().beginTransaction().replace(R.id.container, mFragment, "TAG").commit();
}
}
然后您可以使用mFragment。在您的xml中，您必须将<fragment替换为普通的ViewGroup，FrameLayout例如身份container
答案 2 :(得分：2)
您好，您可以尝试其他方式，例如在您的片段类中创建一个公共静态方法，并从您的活动类On按钮单击调用此方法，并使用所需的纬度和经度。
/*
* Get User Desired Location in fragment class */
public static void getLocation(double lati, double longi)
{
try {
CameraUpdate center = CameraUpdateFactory.newLatLng(new LatLng(lati, longi));
CameraUpdate zoom = CameraUpdateFactory.zoomTo(15);
googleMap.moveCamera(center);
googleMap.animateCamera(zoom);
} catch (Exception e) {
e.printStackTrace();
}
}
/* Get Desired Location in your activity class*/
btnCurrentLocation.setOnClickListener(new OnClickListener()
{
@Override
public void onClick(View v)
{
ClassName.getLocation(lati, longi);
}
});