[英]Google Maps: How to restore markers when resuming map activity
我正在制作一個從傳感器收集數據的應用程序。 每次傳感器發送數據時,都會在地圖上放置一個新標記。 當我按下然后恢復地圖活動時,所有標記都消失了。 有沒有辦法在恢復活動時使用其獨特的 MarkerOptions(標題、片段、LatLng)保存和恢復每個獨特的標記?
這是我的地圖活動
public class MapsActivity extends FragmentActivity implements OnMapReadyCallback, GoogleApiClient.ConnectionCallbacks, GoogleApiClient.OnConnectionFailedListener, LocationListener
{
private GoogleMap mMap;
GoogleApiClient mGoogleApiClient;
Location mLastLocation;
Marker mCurrLocationMarker;
private int co_mV;
private int no2_mV;
LocationRequest mLocationRequest;
private boolean initiateApp;
String currentTime;
TcpClient mTcpClient;
ArrayList<Marker> markerArrayList;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_maps);
if (android.os.Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
checkLocationPermission();
}
// 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);
initiateApp = true;
markerArrayList = new ArrayList<Marker>();
}
/**
* Manipulates the map once available.
* This callback is triggered when the map is ready to be used.
* This is where we can add markers or lines, add listeners or move the camera. In this case,
* we just add a marker near Sydney, Australia.
* If Google Play services is not installed on the device, the user will be prompted to install
* it inside the SupportMapFragment. This method will only be triggered once the user has
* installed Google Play services and returned to the app.
*/
@Override
public void onMapReady(GoogleMap googleMap) {
mMap = googleMap;
mMap.setMapType(GoogleMap.MAP_TYPE_HYBRID);
mMap.setMyLocationEnabled(true);
if(mGoogleApiClient == null) {
//Initialize Google Play Services
if (android.os.Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
if (ContextCompat.checkSelfPermission(this,
Manifest.permission.ACCESS_FINE_LOCATION)
== PackageManager.PERMISSION_GRANTED) {
buildGoogleApiClient();
}
}
else {
buildGoogleApiClient();
}
}
}
/* Here we create the infoWindow **/
protected synchronized void buildGoogleApiClient() {
mGoogleApiClient = new GoogleApiClient.Builder(this)
.addConnectionCallbacks(this)
.addOnConnectionFailedListener(this)
.addApi(LocationServices.API)
.build();
mGoogleApiClient.connect();
}
@Override
public void onConnected(Bundle bundle) {
getNewLocation();
new ConnectTask().execute("");
}
public void newData(JSONObject d) {
try {
co_mV = d.getInt("co_mV");
no2_mV = d.getInt("no2_mV");
} catch (JSONException e) {
e.printStackTrace();
}
getNewLocation();
}
public void getTime() {
Calendar cal = Calendar.getInstance();
currentTime = new SimpleDateFormat("HH:mm:ss").format(cal.getTime());
}
public void getNewLocation() {
mLocationRequest = new LocationRequest();
mLocationRequest.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY);
if (ContextCompat.checkSelfPermission(this,
Manifest.permission.ACCESS_FINE_LOCATION)
== PackageManager.PERMISSION_GRANTED) {
LocationServices.FusedLocationApi.requestLocationUpdates(mGoogleApiClient, mLocationRequest, this);
}
}
@Override
public void onConnectionSuspended(int i) {
}
@Override
public void onLocationChanged(Location location) {
if (markerArrayList.size()>1) {
if(location.distanceTo(mLastLocation) < 30) {
markerArrayList.get(markerArrayList.size()-1).remove();
markerArrayList.remove(markerArrayList.size()-1);
Toast.makeText(
getApplicationContext(),
"Reading to close to last reading, replaces last reading", Toast.LENGTH_SHORT).show();
}
}
if (markerArrayList.size() == 8) {
markerArrayList.get(0).remove();
markerArrayList.remove(0);
}
//Place current location marker
LatLng latLng = new LatLng(location.getLatitude(), location.getLongitude());
if (!initiateApp) {
MarkerOptions markerOptions = new MarkerOptions();
markerOptions.position(latLng);
markerOptions.title("Time of reading: " + currentTime);
markerOptions.snippet("co: " + String.valueOf(co_mV) + " mV, " + "no2: " + String.valueOf(no2_mV) + " mV");
markerOptions.icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_MAGENTA));
mCurrLocationMarker = mMap.addMarker(markerOptions);
markerArrayList.add(mCurrLocationMarker);
}
mLastLocation = location;
Log.d("ADebugTag", "Value: " + Double.toString(location.getLatitude()));
Log.d("ADebugTag", "Value: " + Double.toString(location.getLongitude()));
//move map camera
if(initiateApp){
mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(latLng, 15));
}
boolean contains = mMap.getProjection()
.getVisibleRegion()
.latLngBounds
.contains(latLng);
if(!contains){
mMap.moveCamera(CameraUpdateFactory.newLatLng(latLng));
}
initiateApp = false;
}
@Override
public void onConnectionFailed(ConnectionResult connectionResult) {
}
public static final int MY_PERMISSIONS_REQUEST_LOCATION = 99;
public boolean checkLocationPermission(){
if (ContextCompat.checkSelfPermission(this,
Manifest.permission.ACCESS_FINE_LOCATION)
!= PackageManager.PERMISSION_GRANTED) {
// Asking user if explanation is needed
if (ActivityCompat.shouldShowRequestPermissionRationale(this,
Manifest.permission.ACCESS_FINE_LOCATION)) {
// Show an explanation to the user *asynchronously* -- don't block
// this thread waiting for the user's response! After the user
// sees the explanation, try again to request the permission.
//Prompt the user once explanation has been shown
ActivityCompat.requestPermissions(this,
new String[]{Manifest.permission.ACCESS_FINE_LOCATION},
MY_PERMISSIONS_REQUEST_LOCATION);
} else {
// No explanation needed, we can request the permission.
ActivityCompat.requestPermissions(this,
new String[]{Manifest.permission.ACCESS_FINE_LOCATION},
MY_PERMISSIONS_REQUEST_LOCATION);
}
return false;
} else {
return true;
}
}
@Override
public void onRequestPermissionsResult(int requestCode,
String permissions[], int[] grantResults) {
switch (requestCode) {
case MY_PERMISSIONS_REQUEST_LOCATION: {
// If request is cancelled, the result arrays are empty.
if (grantResults.length > 0
&& grantResults[0] == PackageManager.PERMISSION_GRANTED) {
// permission was granted. Do the
// contacts-related task you need to do.
if (ContextCompat.checkSelfPermission(this,
Manifest.permission.ACCESS_FINE_LOCATION)
== PackageManager.PERMISSION_GRANTED) {
if (mGoogleApiClient == null) {
buildGoogleApiClient();
}
mMap.setMyLocationEnabled(true);
}
} else {
// Permission denied, Disable the functionality that depends on this permission.
Toast.makeText(this, "permission denied", Toast.LENGTH_LONG).show();
}
return;
}
// other 'case' lines to check for other permissions this app might request.
// You can add here other case statements according to your requirement.
}
}
ublic JSONObject getNewJSON(JSONObject json) {
try {
int humidity = json.getInt("humidity_ppm");
int pressure = json.getInt("pressure_Pa");
int noise = json.getInt("noise_dB");
double lat = mLastLocation.getLatitude();
double lng = mLastLocation.getLongitude();
long time = System.currentTimeMillis() / 1000L;
JSONObject c = new JSONObject();
c.put("time",time);
c.put("lat",lat);
c.put("long",lng);
c.put("humidity",humidity);
c.put("pressure",pressure);
c.put("noise_dB",noise);
return c;
} catch (JSONException e) {
e.printStackTrace();
}
return null;
}
public class ConnectTask extends AsyncTask<String, String, TcpClient> {
@Override
protected TcpClient doInBackground(String... message) {
//we create a TCPClient object
mTcpClient = new TcpClient(new TcpClient.OnMessageReceived() {
@Override
//here the messageReceived method is implemented
public void messageReceived(String message) {
//this method calls the onProgressUpdate
publishProgress(message);
}
});
mTcpClient.run();
return null;
}
@Override
protected void onProgressUpdate(String... values) {
super.onProgressUpdate(values);
try {
JSONObject parser = new JSONObject(values[0]);
JSONObject d = parser.getJSONObject("d");
JSONObject cloudData = getNewJSON(d);
if (mLastLocation != null) {
newData(d);
getTime();
}
System.out.println(cloudData);
} catch (JSONException e) {
e.printStackTrace();
}
//process server response here....
}
}
你說
當我按下返回然后恢復地圖時
對? 不關閉您的應用程序。
最簡單的方法是覆蓋onBackPressed
方法,如下所示:
@Override
public void onBackPressed() {
moveTaskToBack(true);
}
這不會再次觸發onDestroy()
和onCreate()
,因此您不會修改您的 Activity 實例。 夠簡單了吧?
您可以創建一個使用來自您的服務器的新數據填充的函數。 然后,您可以在服務器發送 JSON 數據后立即調用該函數。 要回答您的問題,您只需在 onResume 中調用相同的函數即可。 有關活動狀態的更多信息,請閱讀此內容。
另一種方法是將它保存在一個 savedInstanceState 包中,並像這個 SO 接受的答案一樣檢查 onSaveInstanceState 如果該包不為空,如果是這樣,則用列表(標記的最后已知位置,如果這適用於您的項目)。 否則只需加載地圖。
我發現這個答案提供了一個優雅的單行解決方案。 這將在用戶旋轉手機時恢復標記,但在他按下后退按鈕時不會恢復標記(我知道這不是 OP 要求的,但谷歌會引導人們到這里)
在onCreate
添加以下內容:
// mapFragment is a SupportMapFragment
mapFragment.setRetainInstance(true);
在清單文件中,您可以添加以下行:
<activity android:name=".MapsActivity"
android:configChanges="orientation|screenSize">
這是對我有用的最簡單的解決方案之一
@Override
public void onBackPressed() {
moveTaskToBack(true);
}
,並且適用於足夠簡單的應用程序,但也推薦使用 onSaveInstanceState() 方法。 我從我的研究中發現,序列化和反序列化標記列表很困難,而且 onSaveInstanceState() 僅適用於字符串等簡單對象。 如果有人找到更好的解決方案,也請告訴我:)
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