What's wrong with Google Maps development on Android - Part One

on April 12, 2011, 12:23 pm

Update 5th December 2012 - Android Maps v2

This rant is coming from an unabashed Google fanboy. I have always loved Google as a company and the maps API in particular. I write this in the hope that it will help Android become a better place for developers like me.

Also, all the hard work for this post was done by Nick Maher. He blazed the Android development trail for me and most of the insights in this post are his. Some of the hoops that he has jumped through makes Tripview for Android even more impressive.

This fairly inocuous sentence in the Hello MapView tutorial hides a nasty underlying problem with the Google Maps library:

This is a special sub-class of Activity, provided by the Maps library, which provides important map capabilities.

Basically it means if you want to display a google map inside an activity in Android, you need to derive from the MapActivity class. So this isn't so bad right? Well maybe not.

What if you have an activity, GenericToolboxActivity, that does a bunch of different things, one of which involves displaying a map? Forcing GenericToolboxActivity to derive from MapActivity seems kinda dumb.

You can get around that problem by sticking your MapActivity in a LocalActivityManager. The LocalActivityManager is basically a sandbox for your activity. You stick your MapActivity subclass, let's call her JealousSpouseMapActivity, in your LocalActivityManager and gently prod her until she gives up that MapView object that you so desire:

// set up the LAM m_lam = new LocalActivityManager(this, true); // stick the map activity in the LAM Intent intent = new Intent(this, JealousSpouseMapActivity.class); m_lam.dispatchCreate(null); m_lam.dispatchResume(); m_lam.startActivity("map", intent); m_mapActivity = (JealousSpouseMapActivity)m_lam.getActivity("map"); // the view please? return m_mapActivity.getWindow().getDecorView(); // Once I am finished with the view, clean it up m_lam.dispatchPause(true); m_lam.dispatchDestroy(true);

You are essentially lulling your JealousSpouseMapActivity into a false sense of security:

Dear JealousSpouseMapActivity, I would never re-parent any of your stuff. That would be wrong. Put your feet up and relax, i'll just need a pointer to your MapView before I pop off and get you breakfast in bed.

Once you have the MapView you can stick it in your view heirachy for your generic activity and JealousSpouseMapActivity is none the wiser. So why can't this stuff just be done in a MapView class instead? According to the MapActivity documentation its responsibilities include:

  • Activity lifecycle managment - So presumably most activities need to manage their lifecycle, so I wonder how much map specific stuff is done here.
  • Setup and teardown of services behind a MapView - Hrm. If we can have a WebView object that does requests in the background, fairly complex rendering and all sorts of other magical things, I wonder why we can't have a MapView that does the same. What is so "special" about a map that makes it impossible to implement as a view subclass.

In fact thinking about WebView brings up another argument against implementing the map this way. What if our helpful and friendly WebView had some kind of mental break and turned into AngryExGirlfriendWebActivity? What if we had to derive activies that show web content from AngryExGirlfriendWebActivity? If we want to show web and map content at the same time, basically we are screwed, we can't derive from them both. I guess we could try and stick both AngryExGirlfriendWebActivity and JealousSpouseMapActivity into a LocalActivityManager and then gently ask them to give up their respective view goodness, but I can't imagine that is going to end well.

Ok, Perhaps I have taken this analogy a little too far, but you get the idea.

This rant continues:

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