Question

我创建了一个应用，其中三个片段标签中的第一个包含地图。现在只实现了第一个选项卡。您可以在存储库中找到整个应用： https://github.com/lwach87/EarthquakeApp

当我将标签从1移动到3时，应用程序正常构建并运行。当我从标签3尝试回到之前的标签时出现崩溃。我收到运行时异常：

import android.support.design.widget.TabLayout;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.Toolbar;

public class MainActivity extends AppCompatActivity {

    private TabLayout tabLayout;
    private ViewPager viewPager;
    private Toolbar toolbar;

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

        toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        viewPager = (ViewPager) findViewById(R.id.view_pager);
        viewPager.setAdapter(new PagerAdapter(this, getSupportFragmentManager()));

        tabLayout = (TabLayout) findViewById(R.id.tab_layout);
        tabLayout.setupWithViewPager(viewPager);

    }
}

MainActivity.java

public class PagerAdapter extends FragmentPagerAdapter {

    private Context context;

    public PagerAdapter(Context context, FragmentManager fm) {
        super(fm);
        this.context = context;
    }

    @Override
    public Fragment getItem(int position) {
        switch (position) {
            case 0:
                return new MapFragment();
            case 1:
                return new ListFragment();
            case 2:
                return new GraphFragment();
        }

        return null;
    }

    @Override
    public int getCount() {
        return 3;
    }

    @Override
    public CharSequence getPageTitle(int position) {
        switch(position){
            case 0:
                return context.getString(R.string.action_map);
            case 1:
                return context.getString(R.string.action_list);
            case 2:
                return context.getString(R.string.action_graph);
        }
        return null;
    }
}

这是ViewPager的适配器

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

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;

public class MapFragment extends Fragment implements OnMapReadyCallback {

    private GoogleMap mMap;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        View view = inflater.inflate(R.layout.activity_map, container, false);

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

        return view;
    }


    @Override
    public void onMapReady(GoogleMap googleMap) {
        mMap = googleMap;

        // Add a marker in Sydney and move the camera
        LatLng sydney = new LatLng(-34, 151);
        mMap.addMarker(new MarkerOptions().position(sydney).title("Marker in Sydney"));
        mMap.moveCamera(CameraUpdateFactory.newLatLng(sydney));
    }
}

MapFragment

{{1}}

Answer 1

这很可能是因为使用嵌套在ViewPager中使用的Fragment内的SupportMapFragment。

最简单的解决方案是让ViewPager中使用的Fragment直接扩展SupportMapFragment。这消除了嵌套片段的使用。另请注意，此解决方案不需要对xml布局进行充气。

使用以下代码替换MapFragment：

public class MapFragment extends SupportMapFragment implements OnMapReadyCallback {

    private GoogleMap mMap;

    @Override
    public void onResume() {
        super.onResume();

        if (mMap == null) {
            getMapAsync(this);
        }
    }

    @Override
    public void onMapReady(GoogleMap googleMap) {
        mMap = googleMap;

        // Add a marker in Sydney and move the camera
        LatLng sydney = new LatLng(-34, 151);
        mMap.addMarker(new MarkerOptions().position(sydney).title("Marker in Sydney"));
        mMap.moveCamera(CameraUpdateFactory.newLatLng(sydney));
    }
}

在片段选项卡中添加映射时出错

1 个答案: