Question

我有一个使用SectionsPageAdapter的标签式活动。有两个选项卡，每个选项卡使用不同的片段，其中一个是谷歌地图。当我尝试从MapFragment获取SupportMapFragment时，它返回null。

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

我也尝试过：

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

如果我创建一个新的GoogleMapsActivity，它运行得很好，这证实它与我的密钥无关。标识为map的片段存在。

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

注意：CoomonsWare在问题的第一条评论中提供的链接上的代码使我找到了解决方案。

正如CommonsWare所指出的，解决方案是MapFragment扩展SupportMapFragment，这样getMapAsync(this);可以直接调用（无需访问FragmentManager）。然后在SectionsPagerAdapter的getItem()中返回此MapFragment的实例。请注意，onCreateView()不应该有来电/覆盖，而是java.lang.NullPointerException: Attempt to invoke interface method 'void maps.ei.bz.o()' on a null object reference

最终产品：

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;
    }
}

如何将地图添加到选项卡式活动（Android）

1 个答案: