java - 无法正确使用 SharedPreferences

Question

我正在尝试制作一个应用程序来保存一些令人难忘的地方的位置。我正在使用 SharedPreferences 来保存位置，但它没有被保存。每当用户长按保存 map 位置。应用程序工作正常，但重新打开时它会丢失位置。

主要 Activity :

public class MainActivity extends AppCompatActivity {

    TextView textView;
    static   ArrayList<String> addresses = new ArrayList<String>();
    static   ArrayList<LatLng> positions = new ArrayList<LatLng>();
    static ArrayAdapter<String> arrayAdapter;
    ListView listView;
    static int count =0;
    static int flag =0;
    static int pos;
    String countString;

    public void add(View view) {
        flag=0;
        Intent intent = new Intent(this,MapsActivity.class);
        startActivity(intent);
    }

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

        SharedPreferences sharedPreferences = this.getSharedPreferences(" com.example.memorableplaces",MODE_PRIVATE);
        ArrayList<String> latitudes = new ArrayList<>();
        ArrayList<String> longitudes = new ArrayList<>();

        try {
            countString = sharedPreferences.getString("count","0");
        } catch (Exception e) {
            e.printStackTrace();
        }
        count = Integer.parseInt(countString);

        Log.i("count",countString);
        addresses.clear();
        positions.clear();
        latitudes.clear();
        longitudes.clear();

        try {
            addresses = (ArrayList<String>) ObjectSerializer.deserialize(sharedPreferences.getString("addresses", ObjectSerializer.serialize(new ArrayList<>())));
            latitudes = (ArrayList<String>) ObjectSerializer.deserialize(sharedPreferences.getString("lats", ObjectSerializer.serialize(new ArrayList<>())));
            longitudes = (ArrayList<String>) ObjectSerializer.deserialize(sharedPreferences.getString("lons", ObjectSerializer.serialize(new ArrayList<>())));
        } catch (Exception e) {
            e.printStackTrace();
        }

        Log.i("size",Integer.toString(addresses.size()));
        i f(addresses.size() > 0) {
            Log.i("ok","ok");
            for (int i = 0; i < latitudes.size(); i++) {
                positions.add(new LatLng(Double.parseDouble(latitudes.get(i)), Double.parseDouble(longitudes.get(i))));
            }
        }

        textView = findViewById(R.id.textView);
        listView = findViewById(R.id.listView);

        arrayAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, addresses);
        listView.setAdapter(arrayAdapter);

        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                flag=1;
                pos = position;
                Intent intent = new Intent(getApplicationContext(), MapsActivity.class);
                startActivity(intent);
                Log.i("check","see");
            }
         });
    }
}

map Activity :

public class MapsActivity extends FragmentActivity implements OnMapReadyCallback, GoogleMap.OnMapLongClickListener {

    private GoogleMap mMap;
    LocationManager locationManager;
    LocationListener locationListener;
    Marker previous,current;
    int flag;
    int pos;
    String countString;


    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);

        if(grantResults.length>0&&grantResults[0]== PackageManager.PERMISSION_GRANTED)
        {
            if(ContextCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION)==PackageManager.PERMISSION_GRANTED)
            {
                locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER,0,0,locationListener);
            }
        }
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_maps);
        // Obtain the SupportMapFragment and get notified when the map is ready to be used.
        SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
                .findFragmentById(R.id.map);
        mapFragment.getMapAsync(this);
    }




    @Override
    public void onMapReady(GoogleMap googleMap) {

        mMap = googleMap;

       mMap.setOnMapLongClickListener(this);


        if(MainActivity.flag==0) {
            locationManager = (LocationManager) this.getSystemService(Context.LOCATION_SERVICE);

            locationListener = new LocationListener() {
                @Override
                public void onLocationChanged(Location location) {
                    Log.i("Location", location.toString());
                    previous.remove();
                    LatLng position = new LatLng(location.getLatitude(), location.getLongitude());
                    current = mMap.addMarker(new MarkerOptions().position(position).title("You are here").icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_RED)));
                    mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(position, 15));

                    previous = current;


                }

                @Override
                public void onStatusChanged(String provider, int status, Bundle extras) {

                }

                @Override
                public void onProviderEnabled(String provider) {

                }

                @Override
                public void onProviderDisabled(String provider) {

                }
            };

            if (ContextCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
                ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.ACCESS_FINE_LOCATION}, 1);
            } else {
                locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, locationListener);
                Location lastKnownLocation = locationManager.getLastKnownLocation(LocationManager.GPS_PROVIDER);
                LatLng position = new LatLng(lastKnownLocation.getLatitude(), lastKnownLocation.getLongitude());
                previous = mMap.addMarker(new MarkerOptions().position(position).title("You are here").icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_RED)));
                mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(position, 15));
            }
        }
        else
        {
            if (ContextCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
                ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.ACCESS_FINE_LOCATION}, 1);
            }
            LatLng position = MainActivity.positions.get(MainActivity.pos);
            mMap.addMarker(new MarkerOptions().position(position).title(MainActivity.addresses.get(MainActivity.pos)).icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_CYAN)));
            mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(position, 15));
        }





    }





    @Override
    public void onMapLongClick(LatLng latLng) {
        Geocoder geocoder = new Geocoder(this, Locale.getDefault());

        String address = "";

        try {

            List<Address> listAdddresses = geocoder.getFromLocation(latLng.latitude,latLng.longitude,1);

            if (listAdddresses != null && listAdddresses.size() > 0) {
                if (listAdddresses.get(0).getThoroughfare() != null) {
                    if (listAdddresses.get(0).getSubThoroughfare() != null) {
                        address += listAdddresses.get(0).getSubThoroughfare() + " ";
                    }
                    address += listAdddresses.get(0).getThoroughfare();
                }
            }

        } catch (Exception e) {
            e.printStackTrace();
        }

        if (address.equals("")) {
            SimpleDateFormat sdf = new SimpleDateFormat("HH:mm yyyy-MM-dd");
            address += sdf.format(new Date());
        }

        Log.i("yes","all good");

        mMap.addMarker(new MarkerOptions().position(latLng).title(address).icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_CYAN)));

        Log.i("done","good");

        addresses.add(address);
        positions.add(latLng);

        MainActivity.arrayAdapter.notifyDataSetChanged();


        SharedPreferences sharedPreferences = this.getSharedPreferences("com.example.memorableplaces", Context.MODE_PRIVATE);

        try {

            ArrayList<String> latitudes = new ArrayList<>();
            ArrayList<String> longitudes = new ArrayList<>();

            for (LatLng coord : positions) {
                latitudes.add(Double.toString(coord.latitude));
                longitudes.add(Double.toString(coord.longitude));
            }

            sharedPreferences.edit().putString("places", ObjectSerializer.serialize(addresses)).apply();
            sharedPreferences.edit().putString("lats", ObjectSerializer.serialize(latitudes)).apply();
            sharedPreferences.edit().putString("lons", ObjectSerializer.serialize(longitudes)).apply();


        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

ObjectSerializer 类:

public class ObjectSerializer {


    public static String serialize(Serializable obj) throws IOException {
        if (obj == null) return "";
        try {
            ByteArrayOutputStream serialObj = new ByteArrayOutputStream();
            ObjectOutputStream objStream = new ObjectOutputStream(serialObj);
            objStream.writeObject(obj);
            objStream.close();
            return encodeBytes(serialObj.toByteArray());
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    public static Object deserialize(String str) throws IOException {
        if (str == null || str.length() == 0) return null;
        try {
            ByteArrayInputStream serialObj = new ByteArrayInputStream(decodeBytes(str));
            ObjectInputStream objStream = new ObjectInputStream(serialObj);
            return objStream.readObject();
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    public static String encodeBytes(byte[] bytes) {
        StringBuffer strBuf = new StringBuffer();

        for (int i = 0; i < bytes.length; i++) {
            strBuf.append((char) (((bytes[i] >> 4) & 0xF) + ((int) 'a')));
            strBuf.append((char) (((bytes[i]) & 0xF) + ((int) 'a')));
        }

        return strBuf.toString();
    }

    public static byte[] decodeBytes(String str) {
        byte[] bytes = new byte[str.length() / 2];
        for (int i = 0; i < str.length(); i+=2) {
            char c = str.charAt(i);
            bytes[i/2] = (byte) ((c - 'a') << 4);
            c = str.charAt(i+1);
            bytes[i/2] += (c - 'a');
        }
        return bytes;
    }
}

Answer 1

在你的MainActivity中

SharedPreferences sharedPreferences = this.getSharedPreferences(" com.example.memorableplaces",MODE_PRIVATE);

(注意包前的空格)

在您的 MapsActivity 中

SharedPreferences sharedPreferences = this.getSharedPreferences("com.example.memorableplaces", Context.MODE_PRIVATE);

我发现您没有使用 SharedPreferences 的相同 key 来:

主要 Activity

adresses, lats, lons

map Activity

places, lats, lons

您还可以检查首选项是否已正确保存到设备文件资源管理器中的以下位置:

/data/data/YOUR_PACKAGE_NAME/shared_prefs/YOUR_PREFS_NAME.xml