Java 如何在带有TabLayout的ViewPager中获取Google地图片段中的当前位置

我设法实现了一个表格布局。其中一个选项卡中有一个谷歌地图片段。我想请求访问用户位置的权限，然后在当前位置上放置一个标记。到目前为止，对话框没有显示，我不知道为什么。有人能帮我吗

public class MapsFragment extends Fragment implements OnMapReadyCallback{

    GoogleMap mGoogleMap;
    MapView mMapView;
    View mView;
    LocationManager locationManager;
    static final int REQUEST_LOCATION = 1;

    public MapsFragment() {
        // Required empty public constructor
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        mView = inflater.inflate(R.layout.fragment_maps,container,false);
        return mView;
    }

    @Override
    public void onViewCreated(View view, Bundle savedInstanceState){
        super.onViewCreated(view, savedInstanceState);
        mMapView = (MapView) mView.findViewById(R.id.googleMap);
        if(mMapView != null){
            mMapView.onCreate(null);
            mMapView.onResume();
            mMapView.getMapAsync(this);

        }
    }

    @Override
    public void onMapReady(GoogleMap googleMap) {
        mGoogleMap = googleMap;
        googleMap.setMapType(GoogleMap.MAP_TYPE_NORMAL);
        //Initialize Google PLay Services
        if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.M){
            if(ContextCompat.checkSelfPermission(getContext(),
                    Manifest.permission.ACCESS_FINE_LOCATION) == PackageManager.PERMISSION_GRANTED){
                //Location Permission is gratned
                MapsInitializer.initialize(getContext());
                mGoogleMap.setMyLocationEnabled(true);
            }
        }
        googleMap.addMarker(new MarkerOptions().position(new LatLng(36.652527, -121.797277)).title("CSUMB"));
        CameraPosition CSUMB = CameraPosition.builder().target(new LatLng(36.6538, -121.797277)).zoom(16).bearing(0).tilt(45).build();
        googleMap.moveCamera(CameraUpdateFactory.newCameraPosition(CSUMB));
    }

    void getLocation(){
        locationManager = (LocationManager)getActivity()
                .getSystemService(Context.LOCATION_SERVICE);
        getLocation();
        if(ActivityCompat.checkSelfPermission(getContext(), Manifest.permission.ACCESS_FINE_LOCATION)
                != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(getContext(),
                Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED){

        }else{
            Location location = locationManager.getLastKnownLocation(LocationManager.NETWORK_PROVIDER);
            if(location!= null){
                double latti = location.getLatitude();
                double longi = location.getLongitude();
                Toast.makeText(getActivity(),"Location is " + String.valueOf(latti) + ", " + String.valueOf(longi),Toast.LENGTH_LONG);
                Log.e("Maps Fragment", "Location is: " + String.valueOf(latti) + ", " + String.valueOf(longi));
            }
            else{
                Log.e("Maps fragment", "Unable to find current location.");
            }
        }
    }
    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);

        switch (requestCode) {
            case REQUEST_LOCATION:
                getLocation();
                break;
        }
    }
    @Override
    public void onResume() {
        super.onResume();
        mMapView.onResume();
    }

    @Override
    public void onPause() {
        super.onPause();
        mMapView.onPause();
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        mMapView.onDestroy();
    }

    @Override
    public void onLowMemory() {
        super.onLowMemory();
        mMapView.onLowMemory();
    }
}

这与我的答案非常接近，但是，这个答案并没有解释如何使用带有表格布局的ViewPager

首先，要将这一点与其他答案区分开来，您需要使用

instanceItem（）

覆盖在FragmentPagerAdapter中保留对当前片段的引用

另外，请注意，为了将用户的权限请求响应路由到片段，在活动中这里需要使用

onRequestPermissionsResult（）

方法

以下是完整的活动代码：

public class MainActivity extends AppCompatActivity {

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

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

        // Get the ViewPager and set it's PagerAdapter so that it can display items
        viewPager = (ViewPager) findViewById(R.id.viewpager);
        pagerAdapter = new PagerAdapter(getSupportFragmentManager(), MainActivity.this);
        viewPager.setAdapter(pagerAdapter);

        // Give the TabLayout the ViewPager
        TabLayout tabLayout = (TabLayout) findViewById(R.id.tab_layout);
        tabLayout.setupWithViewPager(viewPager);

        // Iterate over all tabs and set the custom view
        for (int i = 0; i < tabLayout.getTabCount(); i++) {
            TabLayout.Tab tab = tabLayout.getTabAt(i);
            tab.setCustomView(pagerAdapter.getTabView(i));
        }
    }

    class PagerAdapter extends FragmentPagerAdapter {

        String tabTitles[] = new String[] { "Tab One", "Tab Two", "Tab Three", };
        public Fragment[] fragments = new Fragment[tabTitles.length];
        Context context;

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

        @Override
        public int getCount() {
            return tabTitles.length;
        }

        @Override
        public Fragment getItem(int position) {

            switch (position) {
                case 0:
                    return new MapFragment();
                case 1:
                    return new BlankFragment();
                case 2:
                    return new BlankFragment();
            }

            return null;
        }

        @Override
        public CharSequence getPageTitle(int position) {
            // Generate title based on item position
            return tabTitles[position];
        }

        public View getTabView(int position) {
            View tab = LayoutInflater.from(MainActivity.this).inflate(R.layout.custom_tab, null);
            TextView tv = (TextView) tab.findViewById(R.id.custom_text);
            tv.setText(tabTitles[position]);
            return tab;
        }

        //This populates your Fragment reference array:
        @Override
        public Object instantiateItem(ViewGroup container, int position) {
            Fragment createdFragment = (Fragment) super.instantiateItem(container, position);
            fragments[position]  = createdFragment;
            return createdFragment;
        }
    }

    @Override
    public void onRequestPermissionsResult(int requestCode,
                                           String permissions[], int[] grantResults) {
        if (requestCode == MapFragment.MY_PERMISSIONS_REQUEST_LOCATION){
            MapFragment mapFragment = (MapFragment) pagerAdapter.fragments[0];
            if (mapFragment != null) {
                mapFragment.onRequestPermissionsResult(requestCode, permissions, grantResults);
            }
        }
        else {
            super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        }
    }
}

结果

首先，位置权限提示：

用户在运行时接受权限后，显示用户的当前位置：

---

您能解释一下为什么我们需要一个片段引用数组吗？@TheLearner是将用户的权限选择从活动传递到片段所需的，调用

mapFragment.onRequestPermissionsResult（）

。请记住，当用户浏览时，ViewPager会根据需要创建和重新创建片段，默认情况下，它会保持当前片段和两侧的片段处于活动状态。因此，为了获得对当前活动片段的引用，需要使用

instanceItem（）

覆盖。感谢您的解释。由于某种原因，我得到了一个错误：在android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2947）的空对象引用上的PagerAdapter.getTabView（int）’没关系，我能够找到它，但我的getTabView从未被调用/我理解您的代码，但从未调用过getTabView方法。我忘了提到我也在使用导航抽屉，但我不认为这会造成问题。你能帮我看一下代码吗？

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:context=".MainActivity">

    <android.support.design.widget.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:theme="@style/AppTheme.AppBarOverlay"
        android:elevation="6dp">

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="?attr/colorPrimary"
            android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
            app:popupTheme="@style/ThemeOverlay.AppCompat.Light"
            android:elevation="0dp" />

        <android.support.design.widget.TabLayout
            android:id="@+id/tab_layout"
            app:tabMode="fixed"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_below="@+id/toolbar"
            android:background="?attr/colorPrimary"
            android:elevation="0dp"
            app:tabTextColor="#d3d3d3"
            app:tabSelectedTextColor="#ffffff"
            app:tabIndicatorColor="#ff00ff"
            android:minHeight="?attr/actionBarSize"
            />

    </android.support.design.widget.AppBarLayout>

    <android.support.v4.view.ViewPager
        android:id="@+id/viewpager"
        android:layout_width="match_parent"
        android:layout_height="fill_parent"
        app:layout_behavior="@string/appbar_scrolling_view_behavior"
        />

</android.support.design.widget.CoordinatorLayout>

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">
    <TextView
        android:id="@+id/custom_text"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:background="?attr/selectableItemBackground"
        android:gravity="center"
        android:textSize="16dip"
        android:textColor="#ffffff"
        android:maxLines="1"
        />
</LinearLayout>

public class MapFragment extends SupportMapFragment
        implements OnMapReadyCallback,
        GoogleApiClient.ConnectionCallbacks,
        GoogleApiClient.OnConnectionFailedListener,
        LocationListener {

    GoogleMap mGoogleMap;
    LocationRequest mLocationRequest;
    GoogleApiClient mGoogleApiClient;
    Location mLastLocation;
    Marker mCurrLocationMarker;

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

        setUpMapIfNeeded();
    }

    private void setUpMapIfNeeded() {

        if (mGoogleMap == null) {
            getMapAsync(this);
        }
    }
    @Override
    public void onPause() {
        super.onPause();

        //stop location updates when Activity is no longer active
        if (mGoogleApiClient != null) {
            LocationServices.FusedLocationApi.removeLocationUpdates(mGoogleApiClient, this);
        }
    }

    @Override
    public void onMapReady(GoogleMap googleMap)
    {
        mGoogleMap=googleMap;
        mGoogleMap.setMapType(GoogleMap.MAP_TYPE_HYBRID);

        //Initialize Google Play Services
        if (android.os.Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            if (ContextCompat.checkSelfPermission(getActivity(),
                    Manifest.permission.ACCESS_FINE_LOCATION)
                    == PackageManager.PERMISSION_GRANTED) {
                //Location Permission already granted
                buildGoogleApiClient();
                mGoogleMap.setMyLocationEnabled(true);
            } else {
                //Request Location Permission
                checkLocationPermission();
            }
        }
        else {
            buildGoogleApiClient();
            mGoogleMap.setMyLocationEnabled(true);
        }
    }

    protected synchronized void buildGoogleApiClient() {
        mGoogleApiClient = new GoogleApiClient.Builder(getActivity())
                .addConnectionCallbacks(this)
                .addOnConnectionFailedListener(this)
                .addApi(LocationServices.API)
                .build();
        mGoogleApiClient.connect();
    }

    @Override
    public void onConnected(Bundle bundle) {
        mLocationRequest = new LocationRequest();
        mLocationRequest.setInterval(1000);
        mLocationRequest.setFastestInterval(1000);
        mLocationRequest.setPriority(LocationRequest.PRIORITY_BALANCED_POWER_ACCURACY);
        if (ContextCompat.checkSelfPermission(getActivity(),
                Manifest.permission.ACCESS_FINE_LOCATION)
                == PackageManager.PERMISSION_GRANTED) {
            LocationServices.FusedLocationApi.requestLocationUpdates(mGoogleApiClient, mLocationRequest, this);
        }
    }

    @Override
    public void onConnectionSuspended(int i) {}

    @Override
    public void onConnectionFailed(ConnectionResult connectionResult) {}

    @Override
    public void onLocationChanged(Location location)
    {
        mLastLocation = location;
        if (mCurrLocationMarker != null) {
            mCurrLocationMarker.remove();
        }

        //Place current location marker
        LatLng latLng = new LatLng(location.getLatitude(), location.getLongitude());
        MarkerOptions markerOptions = new MarkerOptions();
        markerOptions.position(latLng);
        markerOptions.title("Current Position");
        markerOptions.icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_MAGENTA));
        mCurrLocationMarker = mGoogleMap.addMarker(markerOptions);

        //move map camera
        mGoogleMap.moveCamera(CameraUpdateFactory.newLatLng(latLng));
        mGoogleMap.animateCamera(CameraUpdateFactory.zoomTo(11));

        //optionally, stop location updates if only current location is needed
        if (mGoogleApiClient != null) {
            LocationServices.FusedLocationApi.removeLocationUpdates(mGoogleApiClient, this);
        }
    }

    public static final int MY_PERMISSIONS_REQUEST_LOCATION = 99;
    private void checkLocationPermission() {
        if (ContextCompat.checkSelfPermission(getActivity(), Manifest.permission.ACCESS_FINE_LOCATION)
                != PackageManager.PERMISSION_GRANTED) {

            // Should we show an explanation?
            if (ActivityCompat.shouldShowRequestPermissionRationale(getActivity(),
                    Manifest.permission.ACCESS_FINE_LOCATION)) {

                // Show an explanation to the user *asynchronously* -- don't block
                // this thread waiting for the user's response! After the user
                // sees the explanation, try again to request the permission.
                new AlertDialog.Builder(getActivity())
                        .setTitle("Location Permission Needed")
                        .setMessage("This app needs the Location permission, please accept to use location functionality")
                        .setPositiveButton("OK", new DialogInterface.OnClickListener() {
                            @Override
                            public void onClick(DialogInterface dialogInterface, int i) {
                                //Prompt the user once explanation has been shown
                                ActivityCompat.requestPermissions(getActivity(),
                                        new String[]{Manifest.permission.ACCESS_FINE_LOCATION},
                                        MY_PERMISSIONS_REQUEST_LOCATION );
                            }
                        })
                        .create()
                        .show();


            } else {
                // No explanation needed, we can request the permission.
                ActivityCompat.requestPermissions(getActivity(),
                        new String[]{Manifest.permission.ACCESS_FINE_LOCATION},
                        MY_PERMISSIONS_REQUEST_LOCATION );
            }
        }
    }

    @Override
    public void onRequestPermissionsResult(int requestCode,
                                           String permissions[], int[] grantResults) {
        switch (requestCode) {
            case MY_PERMISSIONS_REQUEST_LOCATION: {
                // If request is cancelled, the result arrays are empty.
                if (grantResults.length > 0
                        && grantResults[0] == PackageManager.PERMISSION_GRANTED) {

                    // permission was granted, yay! Do the
                    // location-related task you need to do.
                    if (ContextCompat.checkSelfPermission(getActivity(),
                            Manifest.permission.ACCESS_FINE_LOCATION)
                            == PackageManager.PERMISSION_GRANTED) {

                        if (mGoogleApiClient == null) {
                            buildGoogleApiClient();
                        }
                        mGoogleMap.setMyLocationEnabled(true);
                    }

                } else {

                    // permission denied, boo! Disable the
                    // functionality that depends on this permission.
                    Toast.makeText(getActivity(), "permission denied", Toast.LENGTH_LONG).show();
                }
                return;
            }

            // other 'case' lines to check for other
            // permissions this app might request
        }
    }

}