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PORestoring MapView's state on rotate and on back
 

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  1. PORestoring MapView's state on rotate and on back
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    <p><strong>Background</strong></p> <p>I have a larger application in which I had/have several problems with new Google Maps API. I tried to describe it <a href="https://stackoverflow.com/questions/16171619/markers-disapearing-from-mapview-v2-in-fragment-on-back">in a different question</a> but since it seems too complex I decided to start a new project, as simple as possible and try to reproduce problems. So here it is.</p> <p><strong>The situation</strong></p> <p>I'm using <code>Fragments</code> and want to put <code>MapView</code> inside. I don't want to use <code>MapFragment</code>. The sample project I prepared may be not very beautiful but I tried to make it as simple as possible and it had to contain some elements (again simplified) from the original app. I have one <code>Activity</code> and my custom <code>Fragment</code> with <code>MapView</code> in it, added programatically. The <code>Map</code> contains some points/<code>Markers</code>. After clicking on a <code>Marker</code> the <code>InfoWindow</code> is shown and clicking on it causes next <code>Fragment</code> being shown (with <code>replace()</code> function) in content. </p> <p><strong>The problems</strong></p> <p>There are two issues I have:</p> <ol> <li><p>When the <code>Map</code> with <code>Markers</code> is displayed screen rotation causes <code>Class not found when unmarshalling</code> error with my custom <code>MyMapPoint</code> class - I have no idea why and what it means.</p></li> <li><p>I click the <code>Marker</code> and then <code>InfoWindow</code>. After this I press hardware back button. Now I can see the <code>Map</code> but with no <code>Markers</code> and centered in <code>0,0</code> point.</p></li> </ol> <p><strong>The code</strong></p> <p>MainActivity</p> <pre><code>public class MainActivity extends FragmentActivity { private ArrayList&lt;MyMapPoint&gt; mPoints = new ArrayList&lt;MyMapPoint&gt;(); @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); if (savedInstanceState == null) { mPoints.add(new MyMapPoint(1, new LatLng(20, 10), "test point", "description", null)); mPoints.add(new MyMapPoint(2, new LatLng(10, 20), "test point 2", "second description", null)); Fragment fragment = MyMapFragment.newInstance(mPoints); getSupportFragmentManager().beginTransaction() .add(R.id.contentPane, fragment).commit(); } } } </code></pre> <p>activity_main.xml</p> <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt; &lt;FrameLayout xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/contentPane" android:layout_width="fill_parent" android:layout_height="fill_parent" /&gt; </code></pre> <p>map_fragment.xml</p> <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt; &lt;LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" &gt; &lt;com.google.android.gms.maps.MapView xmlns:map="http://schemas.android.com/apk/res-auto" android:id="@+id/map" android:layout_width="match_parent" android:layout_height="match_parent" /&gt; &lt;/LinearLayout&gt; </code></pre> <p>MyMapFragment</p> <pre><code>public class MyMapFragment extends Fragment implements OnInfoWindowClickListener { public static final String KEY_POINTS = "points"; private MapView mMapView; private GoogleMap mMap; private HashMap&lt;MyMapPoint, Marker&gt; mPoints = new HashMap&lt;MyMapPoint, Marker&gt;(); public static MyMapFragment newInstance(ArrayList&lt;MyMapPoint&gt; points) { MyMapFragment fragment = new MyMapFragment(); Bundle args = new Bundle(); args.putParcelableArrayList(KEY_POINTS, points); fragment.setArguments(args); return fragment; } @Override public void onSaveInstanceState(Bundle outState) { super.onSaveInstanceState(outState); mMapView.onSaveInstanceState(outState); MyMapPoint[] points = mPoints.keySet().toArray( new MyMapPoint[mPoints.size()]); outState.putParcelableArray(KEY_POINTS, points); } @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); if (savedInstanceState == null) { Bundle extras = getArguments(); if ((extras != null) &amp;&amp; extras.containsKey(KEY_POINTS)) { for (Parcelable pointP : extras.getParcelableArrayList(KEY_POINTS)) { mPoints.put((MyMapPoint) pointP, null); } } } else { MyMapPoint[] points = (MyMapPoint[]) savedInstanceState .getParcelableArray(KEY_POINTS); for (MyMapPoint point : points) { mPoints.put(point, null); } } } @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { View layout = inflater.inflate(R.layout.map_fragment, container, false); mMapView = (MapView) layout.findViewById(R.id.map); return layout; } @Override public void onActivityCreated(Bundle savedInstanceState) { super.onActivityCreated(savedInstanceState); mMapView.onCreate(savedInstanceState); setUpMapIfNeeded(); addMapPoints(); } @Override public void onPause() { mMapView.onPause(); super.onPause(); } @Override public void onResume() { super.onResume(); setUpMapIfNeeded(); mMapView.onResume(); } @Override public void onDestroy() { mMapView.onDestroy(); super.onDestroy(); } public void onLowMemory() { super.onLowMemory(); mMapView.onLowMemory(); }; private void setUpMapIfNeeded() { if (mMap == null) { mMap = ((MapView) getView().findViewById(R.id.map)).getMap(); if (mMap != null) { setUpMap(); } } } private void setUpMap() { mMap.setOnInfoWindowClickListener(this); addMapPoints(); } private void addMapPoints() { if (mMap != null) { HashMap&lt;MyMapPoint, Marker&gt; toAdd = new HashMap&lt;MyMapPoint, Marker&gt;(); for (Entry&lt;MyMapPoint, Marker&gt; entry : mPoints.entrySet()) { Marker marker = entry.getValue(); if (marker == null) { MyMapPoint point = entry.getKey(); marker = mMap.addMarker(point.getMarkerOptions()); toAdd.put(point, marker); } } mPoints.putAll(toAdd); } } @Override public void onInfoWindowClick(Marker marker) { Fragment fragment = DetailsFragment.newInstance(); getActivity().getSupportFragmentManager().beginTransaction() .replace(R.id.contentPane, fragment) .addToBackStack(null).commit(); } public static class MyMapPoint implements Parcelable { private static final int CONTENTS_DESCR = 1; public int objectId; public LatLng latLng; public String title; public String snippet; public MyMapPoint(int oId, LatLng point, String infoTitle, String infoSnippet, String infoImageUrl) { objectId = oId; latLng = point; title = infoTitle; snippet = infoSnippet; } public MyMapPoint(Parcel in) { objectId = in.readInt(); latLng = in.readParcelable(LatLng.class.getClassLoader()); title = in.readString(); snippet = in.readString(); } public MarkerOptions getMarkerOptions() { return new MarkerOptions().position(latLng) .title(title).snippet(snippet); } @Override public int describeContents() { return CONTENTS_DESCR; } @Override public void writeToParcel(Parcel dest, int flags) { dest.writeInt(objectId); dest.writeParcelable(latLng, 0); dest.writeString(title); dest.writeString(snippet); } public static final Parcelable.Creator&lt;MyMapPoint&gt; CREATOR = new Parcelable.Creator&lt;MyMapPoint&gt;() { public MyMapPoint createFromParcel(Parcel in) { return new MyMapPoint(in); } public MyMapPoint[] newArray(int size) { return new MyMapPoint[size]; } }; } } </code></pre> <p>If you need to take a look at any other file - let me know. <a href="http://www.scio.pl/maptest.tgz" rel="nofollow noreferrer">Here</a> you can find a complete project, you just have to put your own Maps API KEY in <code>AndroidManifest.xml</code> file.</p> <p><strong>EDIT</strong></p> <p>I managed to make the example even more simple and updated the code above.</p>
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