java - 尝试对空对象引用调用虚拟方法 SupportMapFragment getMapAsync

Question

mapFragment.getMapAsync(this) 在 map 中返回 null

我正在尝试设计一个带有谷歌地图和抽屉导航的应用程序，我不断收到尝试在空对象引用上调用虚拟方法“void com.google.android.gms.maps.SupportMapFragment.getMapAsync(com.google.android.gms.maps.OnMapReadyCallbak)”错误，我不知道我做错了什么

public class MainActivity extends AppCompatActivity implements OnMapReadyCallback {

    private AppBarConfiguration mAppBarConfiguration;

    private GoogleMap mMap;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        /*FloatingActionButton fab = 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();
            }
        });*/

        DrawerLayout drawer = findViewById(R.id.drawer_layout);
        NavigationView navigationView = findViewById(R.id.nav_view);
        // Passing each menu ID as a set of Ids because each
        // menu should be considered as top level destinations.
        mAppBarConfiguration = new AppBarConfiguration.Builder(
                R.id.nav_home, R.id.nav_gallery, R.id.nav_slideshow,
                R.id.nav_tools, R.id.nav_share, R.id.nav_send)
                .setDrawerLayout(drawer)
                .build();
        NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment);
        NavigationUI.setupActionBarWithNavController(this, navController, mAppBarConfiguration);
        NavigationUI.setupWithNavController(navigationView, navController);


        //Implementing Google Map getChildFragmentManager
        SupportMapFragment mapFragment = (SupportMapFragment)this.getSupportFragmentManager().findFragmentById(R.id.map);
        mapFragment.getMapAsync(this);

       /* SupportMapFragment mapFragment = (SupportMapFragment)getSupportFragmentManager().findFragmentById(R.id.map);
        if (mapFragment != null) {
            mapFragment.getMapAsync(this);
        }*/




        //Initializing place
        if (!Places.isInitialized()) {
            Places.initialize(getApplicationContext(), "MY_API_KEY");
        }

        googlePlaceLocation();
        googlePlaceDestination();
    }

    private void googlePlaceLocation(){
      /*//Places Api
        places = (PlaceAutocompleteFragment)getFragmentManager().findFragmentById(R.id.place_location);
        places.setOnPlaceSelectedListener(new PlaceSelectionListener() {
            @Override
            public void onPlaceSelected(Place place) {
                mMap.clear();
                mMap.addMarker(new MarkerOptions().position(place.getLatLng()).title(place.getName().toString()));
                mMap.moveCamera(CameraUpdateFactory.newLatLng(place.getLatLng()));
                mMap.animateCamera(CameraUpdateFactory.newLatLngZoom(place.getLatLng(), 12.0f));


                destination = place.getAddress().toString();
                destination = destination.replace("","+");

            }

            @Override
            public void onError(Status status) {

                Toast.makeText(MapsActivity.this, ""+status.toString(), Toast.LENGTH_SHORT).show();

            }
        });*/
    }

    private void googlePlaceDestination() {


// Initialize the AutocompleteSupportFragment.
        AutocompleteSupportFragment autocompleteFragment = (AutocompleteSupportFragment)
                getSupportFragmentManager().findFragmentById(R.id.place_destination);

        autocompleteFragment.setPlaceFields(Arrays.asList(Place.Field.ID, Place.Field.NAME));

        autocompleteFragment.setOnPlaceSelectedListener(new PlaceSelectionListener() {
            @Override
            public void onPlaceSelected(Place place) {
                // TODO: Get info about the selected place.
                Log.i("TAG", "Place: " + place.getName() + ", " + place.getId());
            }

            @Override
            public void onError(Status status) {
                // TODO: Handle the error.
                Log.i("TAG", "An error occurred: " + status);
            }
        });
    }

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

    @Override
    public boolean onSupportNavigateUp() {
        NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment);
        return NavigationUI.navigateUp(navController, mAppBarConfiguration)
                || super.onSupportNavigateUp();
    }

    @Override
    public void onMapReady(GoogleMap googleMap) {
        mMap = googleMap;
        mMap.addMarker(new MarkerOptions()
                .position(new LatLng(37.7750, 122.4183))
                .title("San Francisco"));

        mMap.animateCamera(CameraUpdateFactory.newLatLngZoom(new LatLng(37.7750, 122.4183), 15));
    }

}

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:showIn="@layout/app_bar_main">

    <fragment
        android:id="@+id/nav_host_fragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:defaultNavHost="true"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:navGraph="@navigation/mobile_navigation" />

   <!-- <fragment
        android:id="@+id/map"
        android:name="com.google.android.gms.maps.SupportMapFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".Welcome" />-->

    <FrameLayout
        android:id="@+id/map"
        android:name="com.google.android.gms.maps.SupportMapFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_below="@+id/nav_host_fragment" />

</androidx.constraintlayout.widget.ConstraintLayout>

<?xml version="1.0" encoding="utf-8"?>
<androidx.drawerlayout.widget.DrawerLayout 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:id="@+id/drawer_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:openDrawer="start">

    <include
        layout="@layout/app_bar_main"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

    <com.google.android.material.navigation.NavigationView
        android:id="@+id/nav_view"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        android:fitsSystemWindows="true"
        app:headerLayout="@layout/nav_header_main"
        app:menu="@menu/activity_main_drawer" />

</androidx.drawerlayout.widget.DrawerLayout>

Answer 1

这对我来说效果很好:

<fragment
    android:id="@+id/map"
    android:name="com.google.android.gms.maps.SupportMapFragment"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_below="@+id/nav_host_fragment" />

您已经定义了带有 id 映射的 FrameLayout。如何自动映射到 fragment ？

此外，在调用 getMapAsync 之前检查 map fragment 的可为空性是一个很好的做法:

SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
        .findFragmentById(R.id.map);
if (mapFragment != null) {
    mapFragment.getMapAsync(this);
}

希望这有帮助!