Problem with draw() on a MapView ItemizedOverlay

Question

Hi,

I am developing an application for the Parisian Metro. One of the functions is a map where you can click the metro stations and see what are the metro lines, and when are the next 4 trains on this station.

I have hence created a MapActivity and an ItemizedOverlay classes.

On my device it is working perfectly, but I am getting some logs from the users with a crash, and I really don't understand what's wrong.

My map activity adds ONE ItemizedOverlay that displays a blue dot for the current user location. This overlay also listens to onTap, which depending on the coordinates of the tap, will try to find metro stations (for which I know the lat/lon coordinates). This is working perfectly.

The stack trace of the crash is:

java.lang.NullPointerException
at com.google.android.maps.OverlayBundle.draw(OverlayBundle.java:42)
at com.google.android.maps.MapView.onDraw(MapView.java:494)
at android.view.View.draw(View.java:6535)
at android.view.ViewGroup.drawChild(ViewGroup.java:1531)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1258)
at android.view.ViewGroup.drawChild(ViewGroup.java:1529)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1258)
at android.view.View.draw(View.java:6538)
at android.widget.FrameLayout.draw(FrameLayout.java:352)
at android.view.ViewGroup.drawChild(ViewGroup.java:1531)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1258)
at android.view.View.draw(View.java:6538)
at android.widget.FrameLayout.draw(FrameLayout.java:352)
at com.android.internal.policy.impl.PhoneWindow$DecorView.draw(PhoneWindow.java:1830)
at android.view.ViewRoot.draw(ViewRoot.java:1349)
at android.view.ViewRoot.performTraversals(ViewRoot.java:1114)
at android.view.ViewRoot.handleMessage(ViewRoot.java:1633)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:123)
at android.app.ActivityThread.main(ActivityThread.java:4363)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:521)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
at dalvik.system.NativeStart.main(Native Method)

Sometimes it comes from different lines but it always finishes crashing at OverlayBunde.java:42

As is does not mention my code, I don't know what's wrong.

You can get the source code of the MapActivity and the the ItemizedOverlay: http://code.google.com/p/metroparis/source/browse/trunk/src/org/bicou/metro/

The activity class is ACarteStations and the overlay class is StationMetroMapOverlay.

I am sorry that the code is in French. I will translate it eventually :) If you need translations about the variable names, just let me know.

Hope you can help me!!

Answer 1

I'm guessing that the following line (#106) in ajouterOverlayPosition() is the reason for your error:

if (l == null) {
        return null;
}

One thing that can happen is that the device fails in finding your location (at lm.getLastKnownLocation(...), line #73). In this case, you return null, and add that null to the mapOverlays at onCreate(). onDraw() tries to draw all the overlays, including this null overlay, and a NullPointerException is thrown.

You should probably treat the null location problem differently (perhaps show an error log, or try again, or use some default location...).