我有一个任务是创建一个地图应用程序，在长按下放置标记并在标记点击时显示标记信息。我还必须将它保存到SQLite中。问题是我被卡住了，似乎有些不对劲。离开app后，SQLite显得空洞。我不知道如何保存它们。欢迎任何帮助。 目标在app上退出要保存在DB中的标记，并在再次启动时重新加载并显示在地图上。 到目前为止，这是我的代码： MainActivity：
private GoogleMap mMap;
private JSONObject httpResponse;
private String markerCountry;
private String markerStreetAddress;
private JSONArray addressArray;
private ArrayList<Markers> markerOptionsList;
private Markers markerForDb;
private LatLng markerPosition;
private int counter=0;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_maps);
SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
.findFragmentById(R.id.map);
mapFragment.getMapAsync(this);
}
@Override
protected void onDestroy() {
if (counter==0){
DatabaseHandler db = new DatabaseHandler(getApplicationContext(),null,null,1);
try{
for (Markers marker : markerOptionsList) {
db.addMarker(marker);
}
}catch (NullPointerException e){
e.printStackTrace();
}finally {
db.close();
}
}
super.onDestroy();
}
@Override
protected void onPause() {
if (counter==0){
DatabaseHandler db = new DatabaseHandler(getApplicationContext(),null,null,1);
try{
for (Markers marker : markerOptionsList) {
db.addMarker(marker);
}
}catch (NullPointerException e){
e.printStackTrace();
}finally {
db.close();
}
}
super.onPause();
}
@Override
protected void onStop() {
if (counter==0){
DatabaseHandler db = new DatabaseHandler(getApplicationContext(),null,null,1);
try{
for (Markers marker : markerOptionsList) {
db.addMarker(marker);
}
}catch (NullPointerException e){
e.printStackTrace();
}finally {
db.close();
}
}
super.onStop();
}
@Override
public void onMapReady(GoogleMap googleMap) {
mMap = googleMap;
mMap.setMyLocationEnabled(true);
mMap.setOnMapLongClickListener(this);
mMap.setOnMarkerClickListener(this);
markerOptionsList = new ArrayList<>();
}
@Override
public void onMapLongClick(LatLng latLng) {
markerPosition = latLng;
mMap.addMarker(new MarkerOptions().position(markerPosition));
getAddress(latLng);
AsyncSaveToDb async2 = new AsyncSaveToDb();
async2.execute(latLng);
}
private void getAddress(LatLng latLng) {
URL url = null;
try {
url = new URL("https://maps.googleapis.com/maps/api/geocode/json?latlng=" + latLng.latitude + "," + latLng.longitude + "&key=AIzaSyBWH6gioY47pZjtCy-lz3rmyYNKVBOZnaA");
} catch (MalformedURLException e) {
e.printStackTrace();
}
Async async = new Async();
async.execute(url);
}
@Override
public boolean onMarkerClick(Marker marker) {
for (Markers markers :markerOptionsList) {
double lat = markers.get_lat();
double lng = markers.get_lng();
LatLng latlng = new LatLng(lat,lng);
if (latlng.equals(marker.getPosition())){
Intent intent = new Intent(getApplicationContext(),com.example.fixxxer.mapclicker.MarkerInfoPage.class);
String addressForText = markers.get_address();
String countryForText = markers.get_country();
String locationForText = markers.get_lat() + ", " + markers.get_lng();
intent.putExtra("address", addressForText);
intent.putExtra("country", countryForText);
intent.putExtra("location", locationForText);
startActivity(intent);
}
}
return true;
}
public class Async extends AsyncTask<URL, Void, JSONArray> {
@Override
protected JSONArray doInBackground(URL... params) {
BufferedReader reader;
InputStream inputStream;
JSONArray results = null;
try {
StringBuilder responseBuilder = new StringBuilder();
HttpURLConnection conn = (HttpURLConnection) params[0].openConnection();
conn.setReadTimeout(10000);
conn.setConnectTimeout(15000);
conn.setRequestMethod("GET");
conn.setDoInput(true);
conn.connect();
inputStream = conn.getInputStream();
reader = new BufferedReader(new InputStreamReader(inputStream));
for (String line; (line = reader.readLine()) != null; ) {
responseBuilder.append(line).append("\n");
}
httpResponse = new JSONObject(responseBuilder.toString());
results = httpResponse.getJSONArray("results");
inputStream.close();
reader.close();
} catch (IOException | JSONException e) {
e.printStackTrace();
}
return results;
}
@Override
protected void onPostExecute(JSONArray resultList) {
addressArray = resultList;
JSONArray responseComponents;
try {
if (addressArray != null) {
JSONObject firstResult = addressArray.getJSONObject(0);
if (firstResult != null) {
responseComponents = firstResult.getJSONArray("address_components");
if (responseComponents != null) {
for (int i = 0; i < responseComponents.length(); i++) {
JSONObject currentComponent = responseComponents.getJSONObject(i);
if (currentComponent.getString("types").contains("country")) {
markerCountry = currentComponent.getString("long_name");
markerStreetAddress = firstResult.getString("formatted_address");
if (markerStreetAddress==null||markerStreetAddress.isEmpty()){
markerStreetAddress="No address available for this location";
}else{
String[] split = markerStreetAddress.split(",");
markerStreetAddress="";
for (int j =0;j<split.length-1;j++){
markerStreetAddress+=split[j];
}
}
}
}
}
}
}
} catch (JSONException e) {
e.printStackTrace();
}
if (markerStreetAddress==null||markerStreetAddress.isEmpty()) {
markerStreetAddress = "No address available for this location";
}
Toast.makeText(getApplicationContext(), "Marker added", Toast.LENGTH_SHORT).show();
}
}
public class AsyncSaveToDb extends AsyncTask<LatLng, Void, Markers>{
@Override
protected Markers doInBackground(LatLng... params) {
markerForDb = new Markers();
markerForDb.set_address(markerStreetAddress);
markerForDb.set_country(markerCountry);
markerForDb.set_lat(params[0].latitude);
markerForDb.set_lng(params[0].longitude);
markerForDb.set_image("image");
return markerForDb;
}
@Override
protected void onPostExecute(Markers markers) {
markers = markerForDb;
markerOptionsList.add(markerForDb);
super.onPostExecute(markers);
}
}
DatabaseHelper类：
private static final int DATABASE_VERSION = 1;
private static final String DATABASE_NAME = "locations.db";
public static final String TABLE_LOCATIONS = "locations";
public static final String COLUMN_ID = "_id";
public static final String COLUMN_ADDRESS = "_address";
public static final String COLUMN_COUNTRY = "_country";
public static final String COLUMN_LAT = "_lat";
public static final String COLUMN_LNG = "_lng";
public static final String COLUMN_IMAGE = "_image";
public DatabaseHandler(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
super(context, DATABASE_NAME, factory, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
String query = "CREATE TABLE " +
TABLE_LOCATIONS + "(" +
COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
COLUMN_ADDRESS + " TEXT, " +
COLUMN_COUNTRY + " TEXT, " +
COLUMN_LAT + " REAL, " +
COLUMN_LNG + " REAL, " +
COLUMN_IMAGE + " TEXT " +
");";
db.execSQL(query);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("DROP TABLE IF EXISTS " + TABLE_LOCATIONS);
onCreate(db);
}
public void addMarker(Markers marker) {
ContentValues values = new ContentValues();
values.put(COLUMN_ADDRESS, marker.get_address());
values.put(COLUMN_COUNTRY, marker.get_country());
values.put(COLUMN_LAT, marker.get_lat());
values.put(COLUMN_LNG, marker.get_lng());
values.put(COLUMN_IMAGE, marker.get_image());
SQLiteDatabase db = getWritableDatabase();
db.insert(TABLE_LOCATIONS, null, values);
db.close();
}
public void deleteMarker(int id) {
SQLiteDatabase db = getWritableDatabase();
db.execSQL("DELETE FROM " + TABLE_LOCATIONS + " WHERE " + COLUMN_ID + "=\"" + id + "\";");
}
public ArrayList<Markers> getExistingMarkers() {
ArrayList<Markers> list = new ArrayList<>();
SQLiteDatabase db = getWritableDatabase();
String query = "SELECT * FROM " + TABLE_LOCATIONS;
Cursor curs = db.rawQuery(query, null);
curs.moveToFirst();
while (!curs.isAfterLast()) {
Markers marker = new Markers(
curs.getString(1),
curs.getString(2),
Double.parseDouble(curs.getString(3)),
Double.parseDouble(curs.getString(4)),
curs.getString(5));
list.add(marker);
}
curs.close();
return list;
}
public Markers getOneMarker(double lat, double lng) {
SQLiteDatabase db = this.getReadableDatabase();
String query = "SELECT * FROM " + TABLE_LOCATIONS + " WHERE " + COLUMN_LAT + "=?" + " AND " + COLUMN_LNG + "=?";
Cursor curs = db.rawQuery(query, new String[]{String.valueOf(lat), String.valueOf(lng)});
if (curs != null)
curs.moveToFirst();
Markers marker = null;
if (curs != null) {
try{
marker = new Markers(curs.getString(1), curs.getString(2), Double.parseDouble(curs.getString(3)), Double.parseDouble(curs.getString(4)), curs.getString(5));
}catch (CursorIndexOutOfBoundsException e){
e.printStackTrace();
}
}
if (curs != null) {
curs.close();
}
return marker;
}
public Markers getfirstMarker() {
SQLiteDatabase db = this.getReadableDatabase();
Markers marker=null;
String query = "SELECT * FROM " + TABLE_LOCATIONS + " LIMIT 1";
Cursor curs = db.rawQuery(query, null);
if (curs != null) {
curs.moveToFirst();
try {
marker = new Markers(curs.getString(1), curs.getString(2), Double.parseDouble(curs.getString(3)), Double.parseDouble(curs.getString(4)), curs.getString(5));
} catch (CursorIndexOutOfBoundsException e) {
e.printStackTrace();
}
}
return marker;
}
数据库实体是标准的：
private int _id;
private String _address;
private String _country;
private double _lat;
private double _lng;
private String _image;
public Markers(int _id, String _address, String _country, double _lat, double _lng, String _image) {
this._id = _id;
this._address = _address;
this._country = _country;
this._lat = _lat;
this._lng = _lng;
this._image = _image;
}
public Markers(String _address, String _country, double _lat, double _lng, String _image) {
this._address = _address;
this._country = _country;
this._lat = _lat;
this._lng = _lng;
this._image = _image;
}
public Markers() {
}
public int get_id() {
return _id;
}
public void set_id(int _id) {
this._id = _id;
}
public String get_address() {
return _address;
}
public void set_address(String _address) {
this._address = _address;
}
public String get_country() {
return _country;
}
public void set_country(String _country) {
this._country = _country;
}
public double get_lat() {
return _lat;
}
public void set_lat(double _lat) {
this._lat = _lat;
}
public double get_lng() {
return _lng;
}
public void set_lng(double _lng) {
this._lng = _lng;
}
public String get_image() {
return _image;
}
public void set_image(String _image) {
this._image = _image;
}
最后是MarkersInfoPage：
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_marker_info_page);
TextView addressText = (TextView) findViewById(R.id.addressView);
TextView countryText = (TextView) findViewById(R.id.countryView);
TextView position = (TextView) findViewById(R.id.latlngText);
String address = getIntent().getStringExtra("address");
String country =getIntent().getStringExtra("country");
String location =getIntent().getStringExtra("location");
addressText.setText(address);
countryText.setText(country);
position.setText(location);
Button backButton = (Button) findViewById(R.id.backButton);
backButton.setOnClickListener(this);
}
@Override
public void onClick(View v) {
super.finish();
}
我被困在这里很久了。任何帮助都是无价的。