Saturday, October 8, 2011

Re: [android-developers] Re: unreasonable NullPointerException in onDestroy()

If you download the source tree (if it ever comes back up again), I
think you might find an interesting read in the code that starts up an
application, I think ActivityThread. It's not too much code, mostly
calling instrumentation in the right places, and provides a nice read
for any systems experienced android hacker, if only to convince you
that there's not something much more complex happening under the
covers :-)

Kris

On Sat, Oct 8, 2011 at 6:30 PM, DraganA <dandric@gmail.com> wrote:
> My bad, I just realised I do call finish in onCreate and return before
> the variable is initialised. Kostya explained most of it. Thanks.
>
> On Oct 8, 6:30 pm, Kostya Vasilyev <kmans...@gmail.com> wrote:
>> Calling finish() from onCreate still results in onDestroy getting called.
>>
>> So if your onCreate calls finish() and returns -- before you initialize
>> the list -- perhaps as part of displaying the license agreement, or
>> something else along those lines -- then in onDestroy the list will
>> still be null. Kaboom!
>>
>> So, +1 to Studio's advice of an if(!null) check. Or else create the list
>> as a member initializer:
>>
>> class MyActivity {
>>      private List<String> list = new ArrayList<String>();
>>      ....
>>
>> }
>>
>> -- Kostya
>>
>> 08.10.2011 21:12, Studio LFP ?????:
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> > Without code samples, I don't think anyone is going to be able to help
>> > you find your issue. I use this all the time and the only time I have
>> > seen it not work was when I made a mistake somewhere else in the code.
>>
>> > I do usually do a null check on things in the onDestory before I use
>> > them because my code can get more complicated as it goes. I end up
>> > changing variables along the way forgetting I'm cleaning them up at
>> > the end.
>>
>> > If you do find a serious bug like this, you'd definitely want to go
>> > through the steps to reproduce it and post a bug reports in the
>> > Android Issue Tracker if someone else hasn't found it already.
>>
>> >http://code.google.com/p/android/issues/list
>>
>> > Steven
>> > Studio LFP
>> >http://www.studio-lfp.com
>>
>> > On Saturday, October 8, 2011 11:53:05 AM UTC-5, DraganA wrote:
>>
>> >     That's the problem, the list is created in onCreate() method and is
>> >     not reassigned or set to null anywhere. I forgot to say, the null
>> >     pointer happens in onDestroy() method in list.clear() line. From that
>> >     I can only deduce that onDestroy() is called before onCreate()
>>
>> >     On Oct 8, 5:42 pm, Studio LFP <studi...@gmail.com> wrote:
>> >     > Based on that, you shouldn't get a crash, but obviously that's
>> >     not the full
>> >     > code you are using.
>>
>> >     > Are you changing that variable at any other point in the code?
>>
>> >     > Steven
>> >     > Studio LFPhttp://www.studio-lfp.com<http://www.studio-lfp.com>
>>
>> >     > On Saturday, October 8, 2011 3:34:15 AM UTC-5, DraganA wrote:
>>
>> >     > > I'm puzzled as to why I'm getting Null pointer exception in the
>> >     > > construct below, knowing the Activity life cycle, it shouldn't
>> >     happen.
>> >     > > Could the clue be in TabActivity??
>>
>> >     > > public class Main extends TabActivity {
>>
>> >     > >     private List<String> list;
>>
>> >     > >     public void onCreate(Bundle savedInstanceState) {
>> >     > >         list = new ArrayList<String>();
>> >     > >     }
>>
>> >     > >     protected void onDestroy() {
>> >     > >         list.clear();
>> >     > >     }
>> >     > > }
>>
>> > --
>> > 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
>> > android-developers+unsubscribe@googlegroups.com
>> > For more options, visit this group at
>> >http://groups.google.com/group/android-developers?hl=en
>>
>> --
>> Kostya Vasilyev
>
> --
> 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
> android-developers+unsubscribe@googlegroups.com
> For more options, visit this group at
> http://groups.google.com/group/android-developers?hl=en

--
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
android-developers+unsubscribe@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/android-developers?hl=en

No comments:

Post a Comment