将MapActivity转为MapFragment后出现bottomAppBar视图找不到错误求助

最近把MapActivity迁移成MapFragment，其他问题都修复了，但碰到这个错误：

No view found for id 0x7f080060 (com.example.policetracker:id/bottomAppBar) for fragment MapFragment{19507fe} (5f780415-46e3-4362-a236-d9b35c95d427 id=0x7f080060)

刚接触Android Studio和XML，附上MapFragment代码和fragment_map布局代码，求解决方法。

MapFragment代码 #

public class MapFragment extends Fragment implements OnMapReadyCallback, ActivityCompat.OnRequestPermissionsResultCallback {

private GoogleMap mMap;
private View mView;

Location currentLocation;
private FusedLocationProviderClient fusedClient;
private static final int REQUEST_CODE = 101;

@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    mView = inflater.inflate(R.layout.fragment_map, container, false);
    return mView;
}

@Override
public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
    fusedClient = LocationServices.getFusedLocationProviderClient(requireActivity());
    getLocation();
}

private void getLocation(){
    if((ActivityCompat.checkSelfPermission(getActivity(), Manifest.permission.ACCESS_FINE_LOCATION
    ) != PackageManager.PERMISSION_GRANTED)
            && (ActivityCompat.checkSelfPermission(
            getActivity(), Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED)){

        ActivityCompat.requestPermissions(getActivity(), new String[]{Manifest.permission.ACCESS_FINE_LOCATION}, REQUEST_CODE);
        return;
    }

    Task<Location> task = fusedClient.getLastLocation();

    task.addOnSuccessListener(new OnSuccessListener<Location>() {
        @Override
        public void onSuccess(Location location) {
            if(location != null){
                SupportMapFragment supportMapFragment = (SupportMapFragment) getChildFragmentManager().findFragmentById(R.id.map);
                assert supportMapFragment != null;
                supportMapFragment.getMapAsync(MapFragment.this);
            }
        }
    });
}

@Override
public void onMapReady(GoogleMap googleMap) {
    mMap = googleMap;
    LatLng latLng = new LatLng(currentLocation.getLatitude(), currentLocation.getLongitude());
    mMap.animateCamera(CameraUpdateFactory.newLatLng(latLng));
    mMap.animateCamera(CameraUpdateFactory.newLatLngZoom(latLng, 17));
}

@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
    super.onRequestPermissionsResult(requestCode, permissions, grantResults);
    if (requestCode == REQUEST_CODE) {
        if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
            getLocation();
        }
    }
}
}

fragment_map布局代码 #

<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.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"
tools:context=".MapFragment">

<androidx.fragment.app.FragmentContainerView
    android:id="@+id/map"
    android:name="com.google.android.gms.maps.SupportMapFragment"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:layout="@android:layout/activity_list_item" />

<com.google.android.material.bottomappbar.BottomAppBar
    android:id="@+id/bottomAppBar"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    app:fabCradleMargin="20dp"
    app:fabCradleVerticalOffset="10dp"
    app:fabCradleRoundedCornerRadius="20dp"
    android:layout_gravity="bottom">

    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/bottomNavigationView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_marginEnd="16dp"
        android:background="@android:color/transparent"
        app:menu="@menu/bottom_nav_menu" />

</com.google.android.material.bottomappbar.BottomAppBar>

<com.google.android.material.floatingactionbutton.FloatingActionButton
    android:id="@+id/fab"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:src="@drawable/baseline_add_24"
    app:layout_anchor="@id/bottomAppBar"
    android:contentDescription="TODO" />

</androidx.coordinatorlayout.widget.CoordinatorLayout>

这个错误的核心原因是你在添加MapFragment时，错误地把它的容器ID指定成了bottomAppBar的ID，而不是布局中专门用来承载Fragment的容器（比如Activity布局里的FrameLayout或FragmentContainerView）。

步骤1：检查并修正宿主Activity的布局 #

打开承载MapFragment的Activity布局文件（比如activity_main.xml），确保里面有一个专门的Fragment容器，示例如下：

<!-- 示例Activity布局 -->
<androidx.coordinatorlayout.widget.CoordinatorLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <!-- 这个是承载MapFragment的容器，ID要和添加Fragment时用的一致 -->
    <androidx.fragment.app.FragmentContainerView
        android:id="@+id/fragment_container"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

</androidx.coordinatorlayout.widget.CoordinatorLayout>

步骤2：正确添加MapFragment到容器 #

在Activity的代码中，添加MapFragment时指定正确的容器ID：

// 在Activity的onCreate方法中
getSupportFragmentManager()
    .beginTransaction()
    .replace(R.id.fragment_container, new MapFragment()) // 这里用fragment_container的ID，不是bottomAppBar
    .commit();

额外修复：MapFragment中的空指针问题 #

你的onMapReady方法直接使用未赋值的currentLocation会导致空指针异常，修改getLocation方法里的成功回调：

task.addOnSuccessListener(new OnSuccessListener<Location>() {
    @Override
    public void onSuccess(Location location) {
        if(location != null){
            currentLocation = location; // 给currentLocation赋值
            SupportMapFragment supportMapFragment = (SupportMapFragment) getChildFragmentManager().findFragmentById(R.id.map);
            assert supportMapFragment != null;
            supportMapFragment.getMapAsync(MapFragment.this);
        }
    }
});

内容的提问来源于stack exchange，提问作者jasagregoric