getsupportfragmentmanager（）.findFragmentById（r.id.map）返回null Google map

Question

我尝试在我的MainActivity上使用google map功能，我有一个空指针返回：getsupportfragmentmanager（）.findFragmentById（r.id.map）；==>返回null

SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.mapApi);

mapfragment将为null，当我使用getMapAsync（this）调用它时；应用程序在启动前就关闭了

 mapFragment.getMapAsync(this); // null pointer variable call getMapAsync 

content_main.xml

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="216dp"
        android:orientation="horizontal">

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

        </fragment>
    </LinearLayout>

public class MainActivity extends AppCompatActivity
        implements  NavigationView.OnNavigationItemSelectedListener , OnMapReadyCallback {



    private GoogleMap map;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
   //setContentView(R.layout.activity_main); didn't work
setContentView(R.layout.content_main); // worked, now i haven't null pointer 
        System.out.println("************************ mapApi:"+R.id.mapApi);

        SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.mapApi);


        System.out.println("************************ mapFragment:"+mapFragment);

        if (mapFragment != null) {

            mapFragment.getMapAsync(this);
        }
}

@Override
public void onMapReady(GoogleMap googleMap) {
    map = googleMap;
    LatLng BordjMenaielGare = new LatLng(36.753162, 3.717716);
    LatLng Blida = new LatLng(36.769038, 3.057451);
    map.addMarker(new MarkerOptions().position(BordjMenaielGare).title("Gare Bordj Menaiel "));
    map.addMarker(new MarkerOptions().position(Blida).title("Gare Agha"));
    map.moveCamera(CameraUpdateFactory.newLatLngZoom(BordjMenaielGare, 10));
}

以下是文件：

映射片段位于content_main.xml上，我将其包含在app_bar_main.xml中，app_bar_main包含在activity_main.xml中，我从MainActivity调用映射

我在StackOverflow中搜索了很多，但没有一个解决方案对我的情况有效

Answer 1

你需要打电话：

// add this (supplying the layout for your activity)
setContentView(R.layout.activity); 

在调用super.oncreate（savedInstanceState）；之后