Java 如何将地图添加到选项卡式活动（Android）

我有一个使用SectionsPageAdapter的选项卡式活动。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。当我试图从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);

如果我创建了一个新的GoogleMapsActivity，它工作得很好，这证实了它与我的密钥无关。id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");
    }
}

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 = 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;
    }
}

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;
    }
}

---

注意：CoomonsWare在对该问题的第一次评论中提供的链接上的代码引导我找到了一个解决方案。

正如Commonware所指出的，解决方案是使

MapFragment

扩展

SupportMapFragment

，这样

getMapAsync（这一点）可以直接调用（无需访问FragmentManager）。然后在SpagerAdapter部分的
getItem（）
中返回此MapFragment的实例。请注意，
onCreateView（）
不应该有调用/重写，它导致
java.lang.NullPointerException:尝试在空对象引用上调用接口方法“void maps.ei.bz.o（）”

最终产品：

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");
    }
}

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 = 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;
    }
}

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;
    }
}

为什么
MapFragment
包含
SupportMapFragment
，而不是
SupportMapFragment
或扩展
SupportMapFragment
？嵌套的片段很麻烦。FWIW，下面是一个示例应用程序，它在一个
ViewPager
中演示了10个地图：这是一个非常有用的响应，它打开了我没有经验的眼睛，但我有点困惑，因为在java术语中
成为SupportMapFragment
和
扩展SupportMapFragment
是同一回事“成为一个
SupportMapFragment
，我的意思是没有子类化它。使用它们不需要扩展
MapFragment
或
SupportMapFragment
。IIRC，我的MapsV2示例中没有一个涉及到扩展
MapFragment
。明白了，我在上面链接的示例中找到了解决方案。谢谢