Izydorr Izydorr - 3 months ago 13
Android Question

Restoring MapView's state on rotate and on back

Background

I have a larger application in which I had/have several problems with new Google Maps API. I tried to describe it in a different question 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.

The situation

I'm using

Fragments
and want to put
MapView
inside. I don't want to use
MapFragment
. 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
Activity
and my custom
Fragment
with
MapView
in it, added programatically. The
Map
contains some points/
Markers
. After clicking on a
Marker
the
InfoWindow
is shown and clicking on it causes next
Fragment
being shown (with
replace()
function) in content.

The problems

There are two issues I have:


  1. When the
    Map
    with
    Markers
    is displayed screen rotation causes
    Class not found when unmarshalling
    error with my custom
    MyMapPoint
    class - I have no idea why and what it means.

  2. I click the
    Marker
    and then
    InfoWindow
    . After this I press hardware back button. Now I can see the
    Map
    but with no
    Markers
    and centered in
    0,0
    point.



The code

MainActivity

public class MainActivity extends FragmentActivity {

private ArrayList<MyMapPoint> mPoints = new ArrayList<MyMapPoint>();

@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();
}
}
}


activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/contentPane"
android:layout_width="fill_parent"
android:layout_height="fill_parent" />


map_fragment.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >

<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" />

</LinearLayout>


MyMapFragment

public class MyMapFragment extends Fragment implements
OnInfoWindowClickListener {

public static final String KEY_POINTS = "points";

private MapView mMapView;
private GoogleMap mMap;
private HashMap<MyMapPoint, Marker> mPoints =
new HashMap<MyMapPoint, Marker>();

public static MyMapFragment newInstance(ArrayList<MyMapPoint> 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) && 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<MyMapPoint, Marker> toAdd =
new HashMap<MyMapPoint, Marker>();
for (Entry<MyMapPoint, Marker> 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<MyMapPoint> CREATOR =
new Parcelable.Creator<MyMapPoint>() {
public MyMapPoint createFromParcel(Parcel in) {
return new MyMapPoint(in);
}

public MyMapPoint[] newArray(int size) {
return new MyMapPoint[size];
}
};

}
}


If you need to take a look at any other file - let me know. Here you can find a complete project, you just have to put your own Maps API KEY in
AndroidManifest.xml
file.

EDIT

I managed to make the example even more simple and updated the code above.

Answer

Here is my fix to the first problem:

It seems that Map is trying to unparcel all the bundle, not just it's own information when I call mMap.onCreate(savedInstanceState) and it has problem with it if I'm using my custom Parcelable class. The solution that worked for me was removing my extras from savedInstanceState as soon as I used them - before I call Map's onCreate(). I do it with savedInstanceState.remove(MY_KEY). Another thing I had to do was to call mMap.onSaveInstanceState() before adding my own information to outState in Fragment's onSaveInstanceState(Bundle outState) function.

And here's how I handled the second one:

I simplified the example project to the bare bones. I was adding raw Markers to the map and if I replace the Fragment with map with another one then after clicking "back" I still got "nulled" map. So I did two things:

  1. saving CameraPosition in onPause() function to restore it in onResume()
  2. setting mMap to null in onPause() so when the Fragment comes back, the Markers are added again by the addMapPoints() function (I had to change it a little bit since I was saving and checking Markers id's).

Here are code samples:

private CameraPosition cp;

...

public void onPause() {
    mMapView.onPause();
    super.onPause();

    cp = mMap.getCameraPosition();
    mMap = null;
}

...

public void onResume() {
    super.onResume();
    setUpMapIfNeeded();
    mMapView.onResume();
    if (cp != null) {
        mMap.moveCamera(CameraUpdateFactory.newCameraPosition(cp));
        cp = null;
    }
}

And to update the camera position in onResume() I had to manually initialize maps. I did it in setUpMap():

private void setUpMap() {
    try {
        MapsInitializer.initialize(getActivity());
    } catch (GooglePlayServicesNotAvailableException e) {
    }
    mMap.setOnInfoWindowClickListener(this);
    mMap.setOnMapLongClickListener(this);
    addMapPoints();
}

I realize that those aren't real solutions - just overrides but it's the best I can do for now and the project must go on. If anyone finds cleaner fixes I'll be grateful for letting me know about them.