Re: [android-developers] Re: why does SharedPreferences framework allow you to insert a preference with a null key - given it can't reload the preferences afterwards?

I did not mean to complain at Nobu - sorry if I sounded harsh :)

I just wanted to point out that my question was not so much what happens but why - and also raise awareness to this buggy and unintuitive behavior- or maybe have someone explain why this is so.

Should we post a bug report ?

On Wednesday, October 30, 2013 8:23:46 PM UTC+2, Kristopher Micinski wrote:

Your question seems more to deal with intention rather than
complaining.  I believe that Nobu's response was merely interpreting
the implementation and trying to interpret it, so there's no use in
trying to complain at him for providing a guess at something he didn't
even write.

kris


On Wed, Oct 30, 2013 at 2:02 PM, Palmer Eldritch <the....@gmail.com> wrote:
>
> On Wednesday, October 30, 2013 7:44:17 PM UTC+2, Nobu Games wrote:
>>
>> I quickly peeked into the source code and well, this is the way how it is
>> programmed. When an exception occurs while the preferences data file gets
>> read, SharedPreferences sets internally an empty map so you start from
>> scratch. I even dug a bit deeper. The XML serializer just ignores NULL keys
>> and creates XML output that cannot be properly read anymore through the map
>> deserialization method which seems to expect an existing key value.
>
>
> My question is really why was it allowed to insert a null key in the first
> place - why not throw a NPE immediately (and say so in the docs) ?
> If you read my links (point 3 here) you will see that null keys are
> perfectly valid :  - they fail only on loading the prefs - taking down
> everything with them
> They should either fix deserialization or prohibit null keys
>>
>>
>> As for why it has been programmed like that... I think the reasoning may
>> be that preferences are not deemed to be of so much importance that it
>> should make the app crash in case of failure. This error state is silently
>> discarded and you start over with the defaults. I think that's a reasonable
>> approach since any app should be able to start over with empty preferences.
>
>
>
> Not at all - Shared Preferences is a documented persistence mechanism - it
> is as reasonable as deleting a database without even saying so
>
>>
>>
>> In this particular case you may have discovered a tiny bug you may want to
>> report. But to be honest, using null keys is a pretty unusual thing to do.
>
>
> Not so (either by mistake or not).
> See the discussions in the SO. Some more I suspect they may have to do with
> null keys :
>
> sharedpreferences - Android - Shared Preferences are lost sometimes - Stack
> Overflow
> http://stackoverflow.com/questions/7943573/android-shared-preferences-are-lost-sometimes
> android - Shared Preferences get lost after shutting down device or killing
> the app - Stack Overflow
> http://stackoverflow.com/questions/9803838/shared-preferences-get-lost-after-shutting-down-device-or-killing-the-app#comment12495021_9803838
>
>>
>>
>> On Wednesday, October 30, 2013 5:48:12 AM UTC-5, Palmer Eldritch wrote:
>>>
>>> The preferences are apparently cleared when one tries to load them when
>>> there is a null key which is bad ! Reproducer :
>>>
>>>     public class XmlExceptionTest extends AndroidTestCase {
>>>         /** Run it twice - on the second run the exception is thrown */
>>>         public void testXmlException() {
>>>             Context ctx = getContext();
>>>             SharedPreferences prefs = PreferenceManager
>>>                 .getDefaultSharedPreferences(ctx); // exception thrown
>>> here (line 18)
>>>             // and apparently it clears the prefs as the condition below
>>> is false
>>>             if (prefs.contains("run_once")) { // false
>>>                 Log.w("XmlExceptionTest",
>>>                     "contains null key :" + prefs.contains(null));
>>>             }
>>>             Editor e = prefs.edit();
>>>             e.putBoolean("run_once", true).commit();
>>>             e.putString(null, "I put a sting with null key").commit();
>>>             assertTrue("Contains null", prefs.contains(null));
>>>             PreferenceManager.getDefaultSharedPreferences(ctx); //
>>> exception
>>>             // NOT thrown here  - why ? - apparently there is a static
>>> factory
>>>             // returning the instance it already constructed
>>>             // e.clear().commit(); // this eliminates the exception
>>>         }
>>>     }
>>>
>>> exception :
>>>
>>>     W/ApplicationContext(): getSharedPreferences
>>>     W/ApplicationContext(): org.xmlpull.v1.XmlPullParserException: Map
>>> value without name attribute: string
>>>     W/ApplicationContext():     at
>>> com.android.internal.util.XmlUtils.readThisMapXml(XmlUtils.java:521)
>>>     W/ApplicationContext():     at
>>> com.android.internal.util.XmlUtils.readThisValueXml(XmlUtils.java:733)
>>>     W/ApplicationContext():     at
>>> com.android.internal.util.XmlUtils.readValueXml(XmlUtils.java:667)
>>>     W/ApplicationContext():     at
>>> com.android.internal.util.XmlUtils.readMapXml(XmlUtils.java:470)
>>>     W/ApplicationContext():     at
>>> android.app.ContextImpl.getSharedPreferences(ContextImpl.java:361)
>>>     W/ApplicationContext():     at
>>> android.preference.PreferenceManager.getDefaultSharedPreferences(PreferenceManager.java:348)
>>>     W/ApplicationContext():     at
>>> gr.uoa.di.android.helpers.test.XmlExceptionTest.testXmlException(XmlExceptionTest.java:18)
>>>     W/ApplicationContext():     at
>>> java.lang.reflect.Method.invokeNative(Native Method)
>>>     W/ApplicationContext():     at
>>> java.lang.reflect.Method.invoke(Method.java:521)
>>>     W/ApplicationContext():     at
>>> junit.framework.TestCase.runTest(TestCase.java:154)
>>>     W/ApplicationContext():     at
>>> junit.framework.TestCase.runBare(TestCase.java:127)
>>>     W/ApplicationContext():     at
>>> junit.framework.TestResult$1.protect(TestResult.java:106)
>>>     W/ApplicationContext():     at
>>> junit.framework.TestResult.runProtected(TestResult.java:124)
>>>     W/ApplicationContext():     at
>>> junit.framework.TestResult.run(TestResult.java:109)
>>>     W/ApplicationContext():     at
>>> junit.framework.TestCase.run(TestCase.java:118)
>>>     W/ApplicationContext():     at
>>> android.test.AndroidTestRunner.runTest(AndroidTestRunner.java:169)
>>>     W/ApplicationContext():     at
>>> android.test.AndroidTestRunner.runTest(AndroidTestRunner.java:154)
>>>     W/ApplicationContext():     at
>>> android.test.InstrumentationTestRunner.onStart(InstrumentationTestRunner.java:520)
>>>     W/ApplicationContext():     at
>>> android.app.Instrumentation$InstrumentationThread.run(Instrumentation.java:1447)
>>>
>>> Posted in SO here and in the relevant thread here - but still no answers
>>>
>>> Any ideas ?
>
> --

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