So fügen Sie eine Karte zu einer Aktivität mit Registerkarten hinzu (Android)

Question

Ich habe eine Aktivität mit Tabs, die einen SectionsPageAdapter verwendet. Es gibt zwei Registerkarten, die jeweils ein anderes Fragment verwenden, von denen eines eine Google Map ist. Wenn ich versuche, das SupportMapFragment von dem MapFragment abzurufen, gibt es null zurück.

SupportMapFragment mapFragment = (SupportMapFragment) getChildFragmentManager() 
       .findFragmentById(R.id.map); 

Ich habe auch versucht:

SupportMapFragment mapFragment = (SupportMapFragment) getFragmentManager() 
       .findFragmentById(R.id.map); 

Wenn ich ein neues GoogleMapsActivity schaffen es funktioniert gut, die bestätigt, dass es nichts mit meinem Schlüssel zu tun hat. Das Fragment mit der ID map existiert.

MainActivity.java

package com.example.frias19o.trackthem2; 

import android.support.design.widget.TabLayout; 
import android.support.design.widget.FloatingActionButton; 
import android.support.design.widget.Snackbar; 
import android.support.v7.app.AppCompatActivity; 
import android.support.v7.widget.Toolbar; 

import android.support.v4.view.ViewPager; 
import android.os.Bundle; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.view.View; 

public class MainActivity extends AppCompatActivity { 

    private SectionsPagerAdapter mSectionsPagerAdapter; 

    private ViewPager mViewPager; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 

     Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); 
     setSupportActionBar(toolbar); 
     // Create the adapter that will return a fragment for each of the three 
     // primary sections of the activity. 
     mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager()); 

     // Set up the ViewPager with the sections adapter. 
     mViewPager = (ViewPager) findViewById(R.id.container); 
     mViewPager.setAdapter(mSectionsPagerAdapter); 

     TabLayout tabLayout = (TabLayout) findViewById(R.id.tabs); 
     tabLayout.setupWithViewPager(mViewPager); 

     FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab); 
     fab.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View view) { 
       Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG) 
         .setAction("Action", null).show(); 
      } 
     }); 
    } 


    @Override 
    public boolean onCreateOptionsMenu(Menu menu) { 
     // Inflate the menu; this adds items to the action bar if it is present. 
     getMenuInflater().inflate(R.menu.menu_map, menu); 
     return true; 
    } 

    @Override 
    public boolean onOptionsItemSelected(MenuItem item) { 
     // Handle action bar item clicks here. The action bar will 
     // automatically handle clicks on the Home/Up button, so long 
     // as you specify a parent activity in AndroidManifest.xml. 
     int id = item.getItemId(); 

     //noinspection SimplifiableIfStatement 
     if (id == R.id.action_settings) { 
      return true; 
     } 

     return super.onOptionsItemSelected(item); 
    } 

} 

MapFragment.java

package com.example.frias19o.trackthem2; 

import android.content.Intent; 
import android.os.Bundle; 
import android.provider.Settings; 
import android.support.annotation.NonNull; 
import android.support.annotation.Nullable; 
import android.support.v4.app.Fragment; 
import android.util.Log; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.Toast; 

import com.google.android.gms.common.ConnectionResult; 
import com.google.android.gms.common.api.GoogleApiClient; 
import com.google.android.gms.location.LocationServices; 
import com.google.android.gms.maps.CameraUpdateFactory; 
import com.google.android.gms.maps.GoogleMap; 
import com.google.android.gms.maps.OnMapReadyCallback; 
import com.google.android.gms.maps.SupportMapFragment; 
import com.google.android.gms.maps.model.LatLng; 
import com.google.android.gms.maps.model.MarkerOptions; 

import org.json.JSONException; 
import org.json.JSONObject; 

/******************************************************************** 
* Fragment for Map 
*********************************************************************/ 
public class MapFragment extends Fragment implements OnMapReadyCallback { 
    private static final String LOGTAG = "MapFragment"; 
    private static final String ARG_SECTION_NUMBER = "section_number"; 
    public static GoogleApiClient mGoogleApiClient; 
    private GoogleMap mMap; 

    public MapFragment() { 
    } 

    public static MapFragment newInstance(int sectionNumber) { 
     MapFragment fragment = new MapFragment(); 
     Bundle args = new Bundle(); 
     args.putInt(ARG_SECTION_NUMBER, sectionNumber); 
     fragment.setArguments(args); 
     return fragment; 
    } 

    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, 
          Bundle savedInstanceState) { 
     View rootView; 
     Toast.makeText(getContext(), "fragment_map", Toast.LENGTH_SHORT).show(); 
     rootView = inflater.inflate(R.layout.activity_maps, container, false); 

     return rootView; 
    } 

    @Override 
    public void onActivityCreated(@Nullable Bundle savedInstanceState) { 
     super.onActivityCreated(savedInstanceState); 

     SupportMapFragment mapFragment = (SupportMapFragment) getFragmentManager() 
       .findFragmentById(R.id.map); 
     mapFragment.getMapAsync(this); // it brakes here because mapFragment is null 
    } 


    @Override 
    public void onMapReady(GoogleMap googleMap) { 
     mMap = googleMap; 
     Log.v(LOGTAG, "map is ready"); 

     LatLng sydney = new LatLng(-34, 151); 
     mMap.addMarker(new MarkerOptions().position(sydney).title("Marker in Sydney")); 
     mMap.moveCamera(CameraUpdateFactory.newLatLng(sydney)); 
     Log.v(LOGTAG, "Added Sydney"); 
    } 
} 

SectionsPagerAdapter.java

package com.example.frias19o.trackthem2; 

import android.support.v4.app.Fragment; 
import android.support.v4.app.FragmentManager; 
import android.support.v4.app.FragmentPagerAdapter; 

/*********************************************************************** 
* A {@link FragmentPagerAdapter} that returns a fragment corresponding to 
* one of the sections/tabs/pages. 
**********************************************************************/ 
public class SectionsPagerAdapter extends FragmentPagerAdapter { 

    public SectionsPagerAdapter(FragmentManager fm) { 
     super(fm); 
    } 

    @Override 
    public Fragment getItem(int position) { 
     // getItem is called to instantiate the fragment for the given page. 
     // Return a ClusterFragment (defined as a static inner class below). 

     Fragment fragment = null; 

     switch (position) { 
      case 0: 
       fragment = MapFragment.newInstance(position + 1); 
       break; 
      case 1: 
       fragment = ClusterFragment.newInstance(position + 1); 
       break; 
      default: 
       break; 
     } 

     return fragment; 
    } 

    @Override 
    public int getCount() { 
     // Show 2 total pages. 
     return 2; 
    } 

    @Override 
    public CharSequence getPageTitle(int position) { 
     switch (position) { 
      case 0: 
       return "SECTION 1"; 
      case 1: 
       return "SECTION 2"; 
     } 
     return null; 
    } 
} 

Answer 1

Anmerkung: Der Code auf dem Link von CoomonsWare im ersten Kommentar versehen auf Die Frage führte mich zu einer Lösung.

Wie durch CommonsWare erwähnt, wurde die Lösung macht MapFragmentSupportMapFragment erstrecken, so getMapAsync(this); kann direkt aufgerufen werden (ohne die FragmentManager zugreifen zu müssen). Dann geben Sie eine Instanz dieses MapFragments in der getItem() von SectionsPagerAdapter zurück. Beachten Sie, dass es keinen Anruf/Überschreibung für onCreateView() sein sollte, es verursacht java.lang.NullPointerException: Attempt to invoke interface method 'void maps.ei.bz.o()' on a null object reference

Endprodukt:

MapFragment.java

package com.example.frias19o.trackthem2; 

import android.os.Bundle; 
import android.support.annotation.Nullable; 
import android.util.Log; 
import com.google.android.gms.common.api.GoogleApiClient; 
import com.google.android.gms.maps.CameraUpdateFactory; 
import com.google.android.gms.maps.GoogleMap; 
import com.google.android.gms.maps.OnMapReadyCallback; 
import com.google.android.gms.maps.SupportMapFragment; 
import com.google.android.gms.maps.model.LatLng; 
import com.google.android.gms.maps.model.MarkerOptions; 

/******************************************************************** 
* Fragment for Map 
*********************************************************************/ 
public class MapFragment extends SupportMapFragment implements OnMapReadyCallback { 
    private static final String LOGTAG = "MapFragment"; 
    private GoogleMap mMap; 

    public MapFragment() { 
    } 

    @Override 
    public void onActivityCreated(@Nullable Bundle savedInstanceState) { 
     super.onActivityCreated(savedInstanceState); 
     getMapAsync(this); 
    } 


    @Override 
    public void onMapReady(GoogleMap googleMap) { 
     mMap = googleMap; 
     Log.v(LOGTAG, "map is ready"); 

     LatLng sydney = new LatLng(-34, 151); 
     mMap.addMarker(new MarkerOptions().position(sydney).title("Marker in Sydney")); 
     mMap.moveCamera(CameraUpdateFactory.newLatLng(sydney)); 
     Log.v(LOGTAG, "Added Sydney"); 
    } 
} 

SectionsPagerAdapter.java

package com.example.frias19o.trackthem2; 

import android.support.v4.app.Fragment; 
import android.support.v4.app.FragmentManager; 
import android.support.v4.app.FragmentPagerAdapter; 

/*********************************************************************** 
* A {@link FragmentPagerAdapter} that returns a fragment corresponding to 
* one of the sections/tabs/pages. 
**********************************************************************/ 
public class SectionsPagerAdapter extends FragmentPagerAdapter { 

    public SectionsPagerAdapter(FragmentManager fm) { 
     super(fm); 
    } 

    @Override 
    public Fragment getItem(int position) { 
     // getItem is called to instantiate the fragment for the given page. 
     // Return a ClusterFragment (defined as a static inner class below). 

     Fragment fragment = null; 

     switch (position) { 
      case 0: 
       fragment = new MapFragment(); 

       break; 
      case 1: 
       fragment = ClusterFragment.newInstance(position + 1); 
       break; 
      default: 
       break; 
     } 

     return fragment; 
    } 

    @Override 
    public int getCount() { 
     // Show 2 total pages. 
     return 2; 
    } 

    @Override 
    public CharSequence getPageTitle(int position) { 
     switch (position) { 
      case 0: 
       return "SECTION 1"; 
      case 1: 
       return "SECTION 2"; 
     } 
     return null; 
    } 
}