Bob,
Thanks for this and other posts. If it weren't for yourself, Mark
Murphy and TreKing I would be pulling my hair out - and its getting
too precious to be doing that these days.
As someone with not a lot of experience in things Android, the Context
is one of the most confusing things to me and I would love to see a
blog article/ Mark Murphy chapter specifically on each of the various
levels of Context returned by the various methods and when they should
be used.
Frankly there are that many posts about:-
* dialogs and conflicts with documentation like this one.
* toasts and leaks (
http://groups.google.com/group/android-developers/browse_thread/thread/de2f0cebec002303/475f545e947a5915?lnk=gst&q=toast+leak+context#475f545e947a5915)
* leaks and using ApplicationContext with long lived objects
"There are two easy ways to avoid context-related memory leaks. The
most obvious one is to avoid escaping the context outside of its own
scope. The example above showed the case of a static reference but
inner classes and their implicit reference to the outer class can be
equally dangerous. The second solution is to use the Application
context. This context will live as long as your application is alive
and does not depend on the activities life cycle. If you plan on
keeping long-lived objects that need a context, remember the
application object. You can obtain it easily by calling
Context.getApplicationContext() or Activity.getApplication()." -
http://developer.android.com/resources/articles/avoiding-memory-leaks.html
* Binder.java having internal comments warning about potential
memory leaks using non-static sub-classes - but nothing in the javadoc
documentation. (Well, maybe experienced Java developers are fully
aware of the references inner classes have on their outer class - but
some of us have very little experience and are putting our apps
alongside yours)
THAT quite frankly confuses the hell out of anyone new to Android.
There doesn't appear to be any real documentation in the developer
Resources area (I apologise if I have missed it) that really explains
what all the different hierarchies of context are, what they give you
or with what types of objects they are to be used. Hopefully I am
correct in saying that every Intent is either passed or receives from
somewhere a Context of some form - but there is little information on
what that is or should be.
I'll be the first to admit that, when I first started and until quite
recently, been passing contexts that are as non-specific or higher up
in the hierarchy as possible with the perhaps misguided opinion that -
" well at least if I leak this it wont keep around anything else
that's not there anyway". Yes, I agree with you I am an idiot who
doesn't know the first thing about leaks, SoftReferences and memory
management. But until I started learning about these things and MAT
and tracking leaks, without a real resource on Contexts - can you
forgive me for succumbing to temptation? After all, until you know
better isn't Java supposed to take care of all this for you?
With the ease of publishing apps on the market, goods apps put out
there by people like yourselves - are next to apps by teenagers with
little experience in Java let alone Android. Bad apps impact the good
ones, not just whilst they are running, but also through the entire
"Android experience" that users get. If an app force closes one gets
this little voice in the back of their head telling them that Android,
and not just that app, is prone to being buggy. When most of the time
it is newbies like me who fail to really understand the Android
environment whinging and complaining about Androids faults when all we
are really doing is externalising our own shortcomings.
On the whole, I love Android, but an article on Context best practice
(or maybe half a chapter, or Appendix table, in one of Mark Murphys
books) is really needed so that Learner drivers like myself don't ruin
the Android experience for everyone.
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