An inner class holds a reference to the object instance that created it;
thus, in the following:
public class Outer
{
public class Inner
{
}
Inner i = new Inner();
}
Outer o = new Outer;
Outer.Inner oi = o.i;
o = null;
// o is still alive because oi references it
oii has a hidden reference (the "outer this") to the enclosing class
instance o. So long as somebody holds a reference to the Inner object, the
reference to the outer object remains alive.
If you mark the enclosing class or enclosing method as static, the inner
class will be a static inner class, which holds no reference to the
enclosing class (and also therefore lacks the ability to reference fields
and methods of the outer class).
Event listeners were a common source of leaks (meaning, longer-lived objects
than intended) in Swing code back in the day. Might try hunting around that
way on Google--there used to be a great article on "four types of lapsed
listeners" back then, that described all of this in more detail.
Ted Neward
Java, .NET, XML Services
Consulting, Teaching, Speaking, Writing
http://www.tedneward.com
> -----Original Message-----
> From: android-developers@googlegroups.com [mailto:android-
> develop...@googlegroups.com] On Behalf Of Nathan
> Sent: Thursday, June 17, 2010 8:44 PM
> To: Android Developers
> Subject: [android-developers] Avoid non-static inner classes in an
> activity?
>
> Since I seem to have caught two activity references in a heapdump,
> where the Activity is set to singleTask.
>
> Romain's advice on avoiding memory leaks includes:
>
> "Avoid non-static inner classes in an activity if you don't control
> their life cycle, use a static inner class and make a weak reference
> to the activity inside"
>
> What does this mean exactly? I can't find any examples, positive, or
> negative for this rule.
>
> I do have some non static inner classes in my activity.
>
> Most of them are anonymous inner classes like this one. I see hundreds
> of them in the samples:
>
> button.setOnClickListener(new Button.OnClickListener() {
> public void onClick(View v) {
> progressHorizontal.incrementSecondaryProgressBy(-1);
> // Title progress is in range 0..10000
> setSecondaryProgress(100 *
> progressHorizontal.getSecondaryProgress());
> }
> });
>
> Are anonymous inner classes okay?
>
> I also see something like this in the samples:
>
> private OnClickListener mStopRepeatingListener = new
> OnClickListener() { . . .
>
> Are member variables points to a non static anonymous inner class
> okay? I might think so because a member variable's lifecycle is
> controlled by the activity's lifecycle.
>
> Or do I assume that all the API samples leak a lot of contexts?
>
> Thanks for any insights
>
> Nathan
>
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