Android:在Google地图中保存地图状态

问题是mMap当你恢复时你是null,然后你不能使用mMap.moveCamera();,例如,这会导致你的应用程序崩溃.

解决方法是在尝试再次使用之前检查是否需要设置地图.

我稍微修改了你的代码,以检查是否需要在onCreate和onResume中设置地图.请注意,我使用onPause而不是onStop,因为它与onResume相对应.

private GoogleMap mMap;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_maps);
    setupMapIfNeeded();
}

private void setupMapIfNeeded() {
    // Obtain the SupportMapFragment and get notified when the map is ready to be used.
    if (mMap == null) {
        SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
                .findFragmentById(R.id.map);
        mapFragment.getMapAsync(this);
    }
}
@Override
public void onMapReady(GoogleMap googleMap) {
    mMap = googleMap;

    MapStateManager mgr = new MapStateManager(this);
    CameraPosition position = mgr.getSavedCameraPosition();
    if (position != null) {
        CameraUpdate update = CameraUpdateFactory.newCameraPosition(position);
        Toast.makeText(this, "entering Resume State", Toast.LENGTH_SHORT).show();
        mMap.moveCamera(update);

        mMap.setMapType(mgr.getSavedMapType());
    }
}

@Override
protected void onPause() {
    super.onPause();
    MapStateManager mgr = new MapStateManager(this);
    mgr.saveMapState(mMap);
    Toast.makeText(this, "Map State has been save?", Toast.LENGTH_SHORT).show();
}

@Override
protected void onResume() {
    super.onResume();
    setupMapIfNeeded();
}

MapstateManager完全一样.

public class MapStateManager {

    private static final String LONGITUDE = "longitude";
    private static final String LATITUDE = "latitude";
    private static final String ZOOM = "zoom";
    private static final String BEARING = "bearing";
    private static final String TILT = "tilt";
    private static final String MAPTYPE = "MAPTYPE";

    private static final String PREFS_NAME ="mapCameraState";

    private SharedPreferences mapStatePrefs;

    public MapStateManager(Context context) {
        mapStatePrefs = context.getSharedPreferences(PREFS_NAME, Context.MODE_PRIVATE);
    }

    public void saveMapState(GoogleMap mapMie) {
        SharedPreferences.Editor editor = mapStatePrefs.edit();
        CameraPosition position = mapMie.getCameraPosition();

        editor.putFloat(LATITUDE, (float) position.target.latitude);
        editor.putFloat(LONGITUDE, (float) position.target.longitude);
        editor.putFloat(ZOOM, position.zoom);
        editor.putFloat(TILT, position.tilt);
        editor.putFloat(BEARING, position.bearing);
        editor.putInt(MAPTYPE, mapMie.getMapType());
        editor.commit();
    }

    public CameraPosition getSavedCameraPosition() {
        double latitude = mapStatePrefs.getFloat(LATITUDE, 0);
        if (latitude == 0) {
            return null;
        }
        double longitude = mapStatePrefs.getFloat(LONGITUDE, 0);
        LatLng target = new LatLng(latitude, longitude);

        float zoom = mapStatePrefs.getFloat(ZOOM, 0);
        float bearing = mapStatePrefs.getFloat(BEARING, 0);
        float tilt = mapStatePrefs.getFloat(TILT, 0);

        CameraPosition position = new CameraPosition(target, zoom, tilt, bearing);
        return position;
    }

    public int getSavedMapType() {
        return mapStatePrefs.getInt(MAPTYPE, GoogleMap.MAP_TYPE_NORMAL);
    }
}