如何防止在片段中重新加载/重新加载MapView？

Question

我在我的应用程序中使用导航栏，每次我选择一个项目时，它都会加载一个片段。

我能够使用相同的文本字段和按钮保存片段的状态，但有一个片段可以加载地图、添加标记、集群并执行AsyncTask。

每次我转到另一个菜单项并返回时，它都会重新加载所有内容，例如AsyncTask、Cluster、Markers。我如何停止此片段以不再重新创建地图并在返回时保存状态：

Udate 1：我更新了代码，但问题仍然存在

主要活动:

public class MainActivity extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener {

    NavigationView navigationView = null;
    Toolbar toolbar = null;
    GoogleMap nMap;
    SparseArray<Fragment> myFragments;
    JSONArray jArray;
    private static final int ERROR_DIALOG_REQUEST = 9001;
    public static final int ID_OF_BEACH = 5;
    //initBeach test = new initBeach();
    //JSONArray jsonArray = test.ExcuteLoad();

    /**
     * ATTENTION: This was auto-generated to implement the App Indexing API.
     * See https://g.co/AppIndexing/AndroidStudio for more information.
     */
    private GoogleApiClient client;
    Fragment fragment;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        myFragments = new SparseArray<>();

        //setTitle("");
        setContentView(R.layout.activity_main);

        if (servicesOK()) {
            try {
                jArray = new LoadJson().execute().get();
            } catch (Exception e) {
                e.printStackTrace();
            }
        } else {
            setContentView(R.layout.activity_main);
        }

        //Set the fragment initially
        FragmentTransaction fragmentTransaction =
                getSupportFragmentManager().beginTransaction();
        fragmentTransaction.replace(R.id.fragment_container, new MainFragment(jArray));
        fragmentTransaction.addToBackStack("1");
        fragmentTransaction.commit();

        toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        //noinspection ConstantConditions
        getSupportActionBar().setDisplayShowTitleEnabled(false);


        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);

        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.setDrawerListener(toggle);
        toggle.syncState();


        navigationView = (NavigationView) findViewById(R.id.nav_view);

        //How to change elements in the header programatically


        navigationView.setNavigationItemSelectedListener(this);
        // ATTENTION: This was auto-generated to implement the App Indexing API.
        // See https://g.co/AppIndexing/AndroidStudio for more information.
        client = new GoogleApiClient.Builder(this).addApi(AppIndex.API).build();
        navigationView.setItemIconTintList(null);

    }

    @Override
    public void onBackPressed() {
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        if (drawer.isDrawerOpen(GravityCompat.START)) {
            drawer.closeDrawer(GravityCompat.START);
        } else {
            super.onBackPressed();
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        //noinspection SimplifiableIfStatement
        return super.onOptionsItemSelected(item);
    }


    @Override
    public boolean onNavigationItemSelected(MenuItem item) {
        // Handle navigation view item clicks here.
        int id = item.getItemId();

        if (id == R.id.nav_camara) {
            fragment = myFragments.get(1);
            // if fragment doesn't exist in myFragments, create one and add to it
            if (fragment == null) {
                fragment = new MainFragment(jArray);
                myFragments.put(1, fragment);
            }
            FragmentTransaction fragmentTransaction =
                    getSupportFragmentManager().beginTransaction();
            fragmentTransaction.replace(R.id.fragment_container, fragment);
            fragmentTransaction.commit();


            // Handle the camera actionn

        } else if (id == R.id.nav_gallery) {
            //Set the fragment initially
            fragment = myFragments.get(2);
            // if fragment doesn't exist in myFragments, create one and add to it
            if (fragment == null) {
                fragment = new GalleryFragment();
                myFragments.put(2, fragment);
            }

            FragmentTransaction fragmentTransaction =
                    getSupportFragmentManager().beginTransaction();
            fragmentTransaction.replace(R.id.fragment_container, fragment);
            fragmentTransaction.commit();


        } else if (id == R.id.nav_search) {
            //Set the fragment initially

            // Handle the camera action

        } else if (id == R.id.nav_manage) {

            // Handle the camera action

        } else if (id == R.id.nav_share) {

        } else if (id == R.id.nav_send) {

        }

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        drawer.closeDrawer(GravityCompat.START);
        return true;
    }

    public boolean servicesOK() {

        int isAvailable = GooglePlayServicesUtil.isGooglePlayServicesAvailable(this);

        if (isAvailable == ConnectionResult.SUCCESS) {
            return true;
        } else if (GooglePlayServicesUtil.isUserRecoverableError(isAvailable)) {
            Dialog dialog =
                    GooglePlayServicesUtil.getErrorDialog(isAvailable, this, ERROR_DIALOG_REQUEST);
            dialog.show();
        } else {
            Toast.makeText(this, "Can't connect to mapping service", Toast.LENGTH_SHORT).show();
        }

        return false;
    }


    @Override
    public void onStart() {
        super.onStart();

        // ATTENTION: This was auto-generated to implement the App Indexing API.
        // See https://g.co/AppIndexing/AndroidStudio for more information.
        client.connect();
        Action viewAction = Action.newAction(
                Action.TYPE_VIEW, // TODO: choose an action type.
                "Main Page", // TODO: Define a title for the content shown.
                // TODO: If you have web page content that matches this app activity's content,
                // make sure this auto-generated web page URL is correct.
                // Otherwise, set the URL to null.
                Uri.parse("http://host/path"),
                // TODO: Make sure this auto-generated app URL is correct.
                Uri.parse("android-app://com.compscitutorials.basigarcia.navigationdrawervideotutorial/http/host/path")
        );
        AppIndex.AppIndexApi.start(client, viewAction);
    }

    @Override
    public void onStop() {
        super.onStop();

        // ATTENTION: This was auto-generated to implement the App Indexing API.
        // See https://g.co/AppIndexing/AndroidStudio for more information.
        Action viewAction = Action.newAction(
                Action.TYPE_VIEW, // TODO: choose an action type.
                "Main Page", // TODO: Define a title for the content shown.
                // TODO: If you have web page content that matches this app activity's content,
                // make sure this auto-generated web page URL is correct.
                // Otherwise, set the URL to null.
                Uri.parse("http://host/path"),
                // TODO: Make sure this auto-generated app URL is correct.
                Uri.parse("android-app://com.compscitutorials.basigarcia.navigationdrawervideotutorial/http/host/path")
        );
        AppIndex.AppIndexApi.end(client, viewAction);
        client.disconnect();
    }


    //AsyincTask to load JSON
    public class LoadJson extends AsyncTask<String, Void, JSONArray> {
        String URLu = "SOME_JSON_URL";


        @Override
        protected JSONArray doInBackground(String... params) {

            try {
                URL url = new URL(URLu);
                HttpURLConnection connection = (HttpURLConnection) url.openConnection();
                connection.connect();
                InputStream stream = connection.getInputStream();
                BufferedReader reader = new BufferedReader(new InputStreamReader(stream));
                StringBuffer buffer = new StringBuffer();
                String line = "";
                while ((line = reader.readLine()) != null) {
                    buffer.append(line);
                }
                String finalJson = buffer.toString();

                JSONObject jsonObject = new JSONObject(finalJson);
                JSONArray jsonArray = jsonObject.getJSONArray("marcadores");

                return jsonArray;
            } catch (Exception e) {
                e.printStackTrace();
                return null;
            }

        }

        @Override
        protected void onPostExecute(JSONArray result) {
            super.onPostExecute(result);
        }

        @Override
        protected void onPreExecute() {
          super.onPreExecute();
        }

    }
}

主片段:

public class MainFragment extends Fragment {
    GoogleMap nMap;
    MapView mapView;
    CameraUpdate update;
    JSONArray array;
    private ClusterManager<ItemCluster> mClusterManager;
    private void parseJSON(JSONArray array) {
        if (mapView != null) {
            nMap = mapView.getMap();
            nMap.getUiSettings().setMyLocationButtonEnabled(false);
            nMap.setMyLocationEnabled(true);
            nMap.getUiSettings().setZoomControlsEnabled(true);
            mClusterManager = new ClusterManager<>(this.getActivity(), nMap);
            nMap.setOnCameraChangeListener(mClusterManager);
            nMap.setInfoWindowAdapter(mClusterManager.getMarkerManager());
            nMap.setOnMarkerClickListener(mClusterManager);
        }

        try {
            //Loading LAT LOng of markers on map
            for (int i = 0; i < array.length(); i++) {
                JSONObject jsonObject = array.getJSONObject(i);
                String locality = jsonObject.getString("nombre");
                String vientos = jsonObject.getString("viento");
                int temp = jsonObject.getInt("temperatura");
                double lat = jsonObject.getDouble("lat");
                double lon = jsonObject.getDouble("lon");
                nMap = mapView.getMap();

                mClusterManager.setRenderer(new OwnIconRendered(getActivity().getApplicationContext(), nMap, mClusterManager));
                ItemCluster offsetItem = new ItemCluster(lat, lon, locality, vientos, temp);
                mClusterManager.addItem(offsetItem);
            }
            LatLng latLon = new LatLng(39.4666667, -0.3666667);
            update = CameraUpdateFactory.newLatLngZoom(latLon, 10);
            nMap.moveCamera(update);

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

    }

    @SuppressLint("ValidFragment")
    public MainFragment(JSONArray input) {
        array = input;
    }
    public MainFragment() {

    }



    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        View rootView = inflater.inflate(R.layout.fragment_main, container, false);
        mapView = (MapView) rootView.findViewById(R.id.map);
        mapView.onCreate(savedInstanceState);

        parseJSON(array);

        // Inflate the layout for this fragment
        setRetainInstance(true);
        return rootView;

    }

    class OwnIconRendered extends DefaultClusterRenderer<ItemCluster> {

        private final IconGenerator mClusterIconGenerator = new IconGenerator(getActivity().getApplicationContext());
        private final TextView mClusterImageView;
        private final ImageView mClusterViento;
        private int tempAvg = 0;
        private final Drawable TRANSPARENT_DRAWABLE = new ColorDrawable(Color.TRANSPARENT);


        public OwnIconRendered(Context context, GoogleMap map,
                               ClusterManager<ItemCluster> clusterManager) {
            super(context, map, clusterManager);

            View clusterIcon = getActivity().getLayoutInflater().inflate(R.layout.info_windows, null);
            mClusterIconGenerator.setContentView(clusterIcon);
            mClusterImageView = (TextView) clusterIcon.findViewById(R.id.maxTmp);
            mClusterViento = (ImageView) clusterIcon.findViewById(R.id.viento);

        }

        @Override
        protected void onBeforeClusterItemRendered(ItemCluster item, MarkerOptions markerOptions) {
            markerOptions.icon(BitmapDescriptorFactory.fromResource(R.drawable.marcador_playa));
            markerOptions.title(item.getTitle());
            super.onBeforeClusterItemRendered(item, markerOptions);
        }

        @Override
        protected void onBeforeClusterRendered(Cluster<ItemCluster> cluster, MarkerOptions markerOptions) {

            tempAvg = 0;
            String vientoStr = null;
            for (ItemCluster item : cluster.getItems()) {
                tempAvg = (item.getTemp()+tempAvg);
            }

            mClusterImageView.setText(String.valueOf(tempAvg/cluster.getSize()));
            if ((tempAvg/cluster.getSize()) > 32) {
                mClusterImageView.setBackgroundResource(R.drawable.temp_32_o_mas);
            } else if ((tempAvg/cluster.getSize()) <= 31 && (tempAvg/cluster.getSize()) >= 25) {
                mClusterImageView.setBackgroundResource(R.drawable.temp_25_a_31);
            } else if ((tempAvg/cluster.getSize()) <= 24 && (tempAvg/cluster.getSize()) >= 20) {
                mClusterImageView.setBackgroundResource(R.drawable.temp_20_a_24);
            } else if ((tempAvg/cluster.getSize()) <= 19 && (tempAvg/cluster.getSize()) >= 15) {
                mClusterImageView.setBackgroundResource(R.drawable.temp_15_a_19);
            } else if ((tempAvg/cluster.getSize()) <= 14 && (tempAvg/cluster.getSize()) >= 10) {
                mClusterImageView.setBackgroundResource(R.drawable.temp_10_a_14);
            } else if ((tempAvg/cluster.getSize()) <= 9 && (tempAvg/cluster.getSize()) >= 5) {
                mClusterImageView.setBackgroundResource(R.drawable.temp_5_a_9);
            } else if ((tempAvg/cluster.getSize()) <= 4) {
                mClusterImageView.setBackgroundResource(R.drawable.temp_4_o_menos);
            }

            for (ItemCluster item : cluster.getItems()) {
                vientoStr = item.getViento();
                if (Objects.equals(vientoStr, "appvalenciaplayas/static/images/viento/viento_NE2.svg")) {
                    mClusterViento.setImageResource(R.drawable.viento_ne2);
                } else if (Objects.equals(vientoStr, "appvalenciaplayas/static/images/viento/viento_NW2.svg")) {
                    mClusterViento.setImageResource(R.drawable.viento_nw2);
                } else if (Objects.equals(vientoStr, "appvalenciaplayas/static/images/viento/viento_E2.svg")) {
                    mClusterViento.setImageResource(R.drawable.viento_e2);
                } else if (Objects.equals(vientoStr, "appvalenciaplayas/static/images/viento/viento_NE1.svg")) {
                    mClusterViento.setImageResource(R.drawable.viento_ne1);
                } else if (Objects.equals(vientoStr, "appvalenciaplayas/static/images/viento/viento_NE3.svg")) {
                    mClusterViento.setImageResource(R.drawable.viento_ne3);
                } else if (Objects.equals(vientoStr, "appvalenciaplayas/static/images/viento/viento_NE4.svg")) {
                    mClusterViento.setImageResource(R.drawable.viento_ne4);
                } else if (Objects.equals(vientoStr, "appvalenciaplayas/static/images/viento/viento_NW1.svg")) {
                    mClusterViento.setImageResource(R.drawable.viento_nw1);
                } else if (Objects.equals(vientoStr, "appvalenciaplayas/static/images/viento/viento_NW3.svg")) {
                    mClusterViento.setImageResource(R.drawable.viento_nw3);
                } else if (Objects.equals(vientoStr, "appvalenciaplayas/static/images/viento/viento_NW4.svg")) {
                    mClusterViento.setImageResource(R.drawable.viento_nw4);
                } else if (Objects.equals(vientoStr, "appvalenciaplayas/static/images/viento/viento_E1.svg")) {
                    mClusterViento.setImageResource(R.drawable.viento_e1);
                } else if (Objects.equals(vientoStr, "appvalenciaplayas/static/images/viento/viento_E3.svg")) {
                    mClusterViento.setImageResource(R.drawable.viento_e3);
                } else if (Objects.equals(vientoStr, "appvalenciaplayas/static/images/viento/viento_E4.svg")) {
                    mClusterViento.setImageResource(R.drawable.viento_e4);
                } else if (Objects.equals(vientoStr, "appvalenciaplayas/static/images/viento/viento_N1.svg")) {
                    mClusterViento.setImageResource(R.drawable.viento_n1);
                } else if (Objects.equals(vientoStr, "appvalenciaplayas/static/images/viento/viento_N2.svg")) {
                    mClusterViento.setImageResource(R.drawable.viento_n2);
                } else if (Objects.equals(vientoStr, "appvalenciaplayas/static/images/viento/viento_N3.svg")) {
                    mClusterViento.setImageResource(R.drawable.viento_n3);
                } else if (Objects.equals(vientoStr, "appvalenciaplayas/static/images/viento/viento_N4.svg")) {
                    mClusterViento.setImageResource(R.drawable.viento_n4);
                } else if (Objects.equals(vientoStr, "appvalenciaplayas/static/images/viento/viento_W1.svg")) {
                    mClusterViento.setImageResource(R.drawable.viento_w1);
                } else if (Objects.equals(vientoStr, "appvalenciaplayas/static/images/viento/viento_W2.svg")) {
                    mClusterViento.setImageResource(R.drawable.viento_w2);
                } else if (Objects.equals(vientoStr, "appvalenciaplayas/static/images/viento/viento_W3.svg")) {
                    mClusterViento.setImageResource(R.drawable.viento_w3);
                } else if (Objects.equals(vientoStr, "appvalenciaplayas/static/images/viento/viento_W4.svg")) {
                    mClusterViento.setImageResource(R.drawable.viento_w4);
                } else if (Objects.equals(vientoStr, "appvalenciaplayas/static/images/viento/viento_SW1.svg")) {
                    mClusterViento.setImageResource(R.drawable.viento_sw1);
                } else if (Objects.equals(vientoStr, "appvalenciaplayas/static/images/viento/viento_SW2.svg")) {
                    mClusterViento.setImageResource(R.drawable.viento_sw2);
                } else if (Objects.equals(vientoStr, "appvalenciaplayas/static/images/viento/viento_SW3.svg")) {
                    mClusterViento.setImageResource(R.drawable.viento_sw3);
                } else if (Objects.equals(vientoStr, "appvalenciaplayas/static/images/viento/viento_SW4.svg")) {
                    mClusterViento.setImageResource(R.drawable.viento_sw4);
                } else if (Objects.equals(vientoStr, "appvalenciaplayas/static/images/viento/viento_SE1.svg")) {
                    mClusterViento.setImageResource(R.drawable.viento_se1);
                } else if (Objects.equals(vientoStr, "appvalenciaplayas/static/images/viento/viento_SE2.svg")) {
                    mClusterViento.setImageResource(R.drawable.viento_se2);
                } else if (Objects.equals(vientoStr, "appvalenciaplayas/static/images/viento/viento_SE3.svg")) {
                    mClusterViento.setImageResource(R.drawable.viento_se3);
                } else if (Objects.equals(vientoStr, "appvalenciaplayas/static/images/viento/viento_SE4.svg")) {
                    mClusterViento.setImageResource(R.drawable.viento_se4);
                } else if (Objects.equals(vientoStr, "appvalenciaplayas/static/images/viento/viento_S1.svg")) {
                    mClusterViento.setImageResource(R.drawable.viento_s1);
                } else if (Objects.equals(vientoStr, "appvalenciaplayas/static/images/viento/viento_S2.svg")) {
                    mClusterViento.setImageResource(R.drawable.viento_s2);
                } else if (Objects.equals(vientoStr, "appvalenciaplayas/static/images/viento/viento_S3.svg")) {
                    mClusterViento.setImageResource(R.drawable.viento_s3);
                } else if (Objects.equals(vientoStr, "appvalenciaplayas/static/images/viento/viento_S4.svg")) {
                    mClusterViento.setImageResource(R.drawable.viento_s4);
                }
                break;
            }


            mClusterIconGenerator.setBackground(TRANSPARENT_DRAWABLE);
            Bitmap bitmap = mClusterIconGenerator.makeIcon(String.valueOf(cluster.getSize()));
            markerOptions.icon(BitmapDescriptorFactory.fromBitmap(bitmap));
        }


        @Override
        protected boolean shouldRenderAsCluster(Cluster cluster) {
            // Always render clusters.
            return cluster.getSize() > 1;
        }
    }


    @Override
    public void onResume() {
        super.onResume();
        mapView.onResume();
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        mapView.onDestroy();
    }

    @Override
    public void onPause() {
        super.onPause();
        mapView.onPause();
    }

    @Override
    public void onLowMemory() {
        super.onLowMemory();
        mapView.onLowMemory();
    }

    @Override
    public void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        mapView.onSaveInstanceState(outState);
    }
}

Answer 1

谷歌地图的文档说：

此类的用户必须将包含此视图的活动或片段中的所有生命周期方法转发到此类中的相应方法。特别是，您必须转发以下方法：

• onCreate（Bundle）
• onResume（）
• onPause（）
• onDestroy（）
• onSaveInstanceState（）
• onLowMemory（）

因此，在您的MainFragment.java中，您必须覆盖上述所有方法并将调用委托给mapView。

为了清楚起见，你可以覆盖 onSaveInstanceState（），如下所示：

@Override
public void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    mapView.onSaveInstanceState(outState);
}

另一个问题是您第一次创建< code>MainFragment时没有缓存它。这意味着当您从抽屉中取回一个实例时，您不会“重用”该实例(您可以通过按此顺序单击抽屉项目来检查< code>nav_gallery -

Fragment fragment = new MainFragment(jArray);
myFragments.put(1, fragment);

//Set the fragment initially
FragmentTransaction fragmentTransaction =
        getSupportFragmentManager().beginTransaction();
fragmentTransaction.replace(R.id.fragment_container, fragment);
fragmentTransaction.addToBackStack("1");
fragmentTransaction.commit();

为了保持碎片的状态，您必须执行以下操作：

>

更新onSaveInstanceState（），以保存其状态，如下所示：

@Override
public void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    mapView.onSaveInstanceState(outState);
    outState.putString("jsonArr", jsonArray.toString());
    // TODO put more things which you need to.
}

更新您的onCreateView（），以恢复状态，如：

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    if (savedInstanceState != null) {
        String jsonArrString = savedInstanceState.getString("jsonArr");
        try {
            jsonArray = new JSONArray(jsonArrString);
        }
        catch (Exception e) {
            e.printStackTrace()
        }
    }
    // TODO your old code goes after this line.
}

Answer 2

您将在每个事件后替换片段，请将片段添加到后堆栈，然后从后堆栈中弹出它。然后它就会起作用。检查以下代码：

FragmentManager fragmentManager = getFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.add(android.R.id.content, testFragment);
fragmentTransaction.addToBackStack(TAG);
fragmentTranscation.commit();