Hi Justin, I too have spent a great deal of time debugging this - with little luck. Thanks for taking the time to explain your findings, it does help to understand what was going on.
In the end I chose to redesign my application and use just the one MapView - mainly due to the memory issues. The reason I found myself in this problem was due to the fact I needed a TabHost and a MapView in the same activity. However I found I couldn't extend both a TabActivity and MapActivity in the same Activity so I opted to create my own "TabbedMapActivity", created using the Android source code. I explained it all here if you want to see how I achieved this: http://groups.google.com/group/android-developers/browse_thread/thread/81631e00bd25ee83/8e28418d64337ebb?lnk=gst&q=mscwd01#8e28418d64337ebb Ultimately, I believe you are right, having multiple MapViews will inevitable lead to memory issues regardless of how careful you are to save map states and recycle resources; so I think using just the one MapView is the only answer at this moment in time. Thanks On Dec 9, 11:49 pm, "Justin (Google Employee)" <[EMAIL PROTECTED]> wrote: > Once upon a time I spent a lot of time debugging this issue, so here > is what I found. > > ***WARNING: This information was valid on an internal version of the > SDK between M5-RC15 and 0.9 beta, it may no longer be valid, test > thoroughly and proceed with caution.*** > > First, some information about MapView and MapActivity. Each Android > process may have multiple MapViews and MapActivitys, but they all > manipulate a single MapView backing object. This is because MapViews > take a *huge* amount of memory, roughly half of the 16MB allowed to > each application. This *also means* you need to be very careful about > your memory usage when using MapView. Make sure to use DDMS to analyze > memory usage to make sure you don't run out of space. Because a single > view backs all map views in an application, you also need to save and > restore the map state (including center position and zoom) when your > MapActivity subclass pauses/resumes. > > For the purposes of discussion I will refer to two activities, > ActivityAlpha and ActivityBeta, each is a subclass of MapActivity and > has a MapView. ActivityAlpha starts ActivityBeta. The user will > eventually return to ActivityAlpha either via the 'back' button or > ActivityBeta finishing naturally. > > When ActivityBeta finishes, there are two issues that I believe causes > the problem you see: > > 1) onCreate is not called on the launching ActivityAlpha, onResume is > 2) a certain UI focal change doesn't occur > > Certain initialization of the MapView and various helper entities are > done by MapActivity when onCreate is called. When ActivityBeta is > launched, onPause is called on ActivityAlpha and the helpers for the > MapView are stopped. onResume does some of the restarting, but clearly > not all that is necessary. This can be worked around by calling > super.onCreate(null) from your onResume or onActivityResult method of > your launching MapActivity subclass. ***WARNING***: This is > potentially very dangerous, MapActivity may not expect to be abused > this way, test thoroughly and proceed with caution. > > The second issue results in the above hack not quite working. When > ActivityBeta finishes, and the above hack is applied, ActivityAlpha is > ready to load tiles, but it won't until the MapView is touched so that > the MapView checks to see if it needs tiles. So far, I don't have a > workaround for this, possibly a programmatic pan or zoom would cause > the MapView to load any missing tiles. Some of my previous testing > also indicated that any missing tiles would load when ActivityAlpha > resumes if you use startActivity() to start ActivityBeta instead of > startActivityForResult(). > > The bottom line is that maps were never designed to have multiple map > views in a single application, they're very heavy objects. Hopefully > this helps and is still valid information, let me know how it goes. > > Cheers, > Justin > Android Team @ Google > > On Dec 8, 5:39 pm, mscwd01 <[EMAIL PROTECTED]> wrote: > > > Having tried the test you suggested it seems I can go back and forth > > between my Activity1 map and the inbuilt Google Maps app perfectly > > fine - no memory worries. However my application, constantly throws up > > OutOfMemory errors. > > > One thing I have noticed is after Activity1 calls Activity2, Activity1 > > is never able to load additional tiles. It seems Activity2, even if it > > is destroyed after pressing the back button and returning to Activity1 > > always retains some kind of "focus" - If you reopen Activity 2, the > > map is able to load new tiles. Very strange... > > > On Dec 8, 11:47 pm, Mark Murphy <[EMAIL PROTECTED]> wrote: > > > > mscwd01 wrote: > > > > > Hope I havent confused you ;) > > > > No, but you have made my head hurt. > > > > > Oh btw I purchased your "The Busy Coder's Guide to Android > > > > Development" book - its very helpful ;) > > > > My head feels better now... ;-) > > > > > However what i'm asking is, is there a way to kill off Activity2 > > > > completely when pressing the Back button to return to Activity1 and > > > > return full control to the first map? > > > > Well, you already tried the stock answer of using finish(). With your > > > kill-my-process hack, you're heading down in a direction which, on my > > > map of Android, is labeled "Here There Be Dragons"... > > > > > I believe I am making more and > > > > > more map objects when I launch Activity2 again and again and not > > > > releasing resources when I finish with it? > > > > Or they're just not getting garbage collected fast enough or something. > > > > I have a suggestion. I have no idea how crazy it will be for you to > > > utilize if it works. > > > > In Activity1, temporarily replace launching Activity2 with a > > > startActivity() that launches the built-in Maps application. You should > > > be able to do this through: > > > > startActivity(new Intent(Intent.ACTION_VIEW, Uri.parse("geo:40,-75"))); > > > > which will give you a map of the NJ side of the Philadelphia suburbs. > > > > Now, try bouncing back and forth between your Activity1 and the Maps > > > application, like you were bouncing between Activity1 and Activity2. > > > > If things fail as before, I think you may just be screwed, at least in > > > terms of rapidly flipping between two MapView instances. They may make > > > too much garbage. > > > > If, however, this holds up, it may be you can only effectively have one > > > MapView per *application* if you want to rapidly switch between them. In > > > that case, your mission (should you choose to accept it) is to split > > > your project into two separate applications. This would suck mightily, > > > particularly if you were looking to deploy via a market, but it's > > > possible it is the best way for you to get two stable MapViews under > > > your control. > > > > If it were me, I'd try very very hard to get by with one map, somehow. > > > > -- > > > Mark Murphy (a Commons Guy)http://commonsware.com > > > _The Busy Coder's Guide to Android Development_ Version 1.9 Available! --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Android Developers" group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/android-developers?hl=en -~----------~----~----~----~------~----~------~--~---
