找不到MapActivity类中的Mapview

import com.google.android.gms.maps.MapView;

<com.google.android.gms.maps.MapView
    android:id="@+id/mapView"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

<meta-data
    android:name="com.google.android.geo.API_KEY"
    android:value="YOUR_API_KEY" />

implementation 'com.google.android.gms:play-services-maps:17.0.1'

MapView mapView = findViewById(R.id.mapView);
mapView.onCreate(savedInstanceState);
mapView.getMapAsync(this);

public class MapActivity extends AppCompatActivity implements OnMapReadyCallback {
    // ...
    @Override
    public void onMapReady(GoogleMap googleMap) {
        // 在这里添加地图相关的操作
    }
}