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POWhat is triggering this Exception instance: "java.lang.IllegalArgumentException: The observer is null." and how could it be avoid?
 

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  1. POWhat is triggering this Exception instance: "java.lang.IllegalArgumentException: The observer is null." and how could it be avoid?
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    <p>I'm getting this exception when returning to the original <code>ListActivity</code> after opening an new activity with the content of the item selected by the user. It only occurs on Ice Cream Sandwich.</p> <p>This is the trace:</p> <pre><code> java.lang.IllegalArgumentException: The observer is null. at android.database.Observable.unregisterObserver(Observable.java:59) at android.widget.BaseAdapter.unregisterDataSetObserver(BaseAdapter.java:42) at android.widget.AbsListView.onDetachedFromWindow(AbsListView.java:2373) at android.view.View.dispatchDetachedFromWindow(View.java:9756) at android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:2274) at android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:2272) at android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:2272) at android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:2272) at android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:2272) at android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:2272) at android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:2272) at android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:2272) at android.view.ViewRootImpl.dispatchDetachedFromWindow(ViewRootImpl.java:2227) at android.view.ViewRootImpl.doDie(ViewRootImpl.java:3679) at android.view.ViewRootImpl.die(ViewRootImpl.java:3667) at android.view.WindowManagerImpl.removeViewImmediate(WindowManagerImpl.java:320) at android.view.WindowManagerImpl$CompatModeWrapper.removeViewImmediate(WindowManagerImpl.java:139) at android.app.ActivityThread.handleDestroyActivity(ActivityThread.java:3144) at android.app.ActivityThread.access$1200(ActivityThread.java:122) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1179) at android.os.Handler.dispatchMessage(Handler.java:99) at android.os.Looper.loop(Looper.java:137) at android.app.ActivityThread.main(ActivityThread.java:4340) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:511) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551) at dalvik.system.NativeStart.main(Native Method) </code></pre> <p>None of my code is mentioned in the stack so it's really puzzling me and I can't event do a dirty catch :/</p> <p>I am registering an anonymous <code>DataSetObserver</code> only when the activity is created. Also the activity is embedded inside an ActivityGroup (which is deprecated in 4.0 but should still suport it, I was hoping).</p> <p>Has anybody had this problem with the new OS?</p> <p>Thanks in advance.</p> <hr> <p><strong>Update:</strong></p> <p>Ok, think I found the source of the problem although not sure how to resolve it. </p> <p>Inside <code>AbsListView.onDetachedFromWindow()</code> We have this:</p> <pre><code>if (mAdapter != null) { // Android code added on ICS mAdapter.unregisterDataSetObserver(mDataSetObserver); mDataSetObserver = null; } </code></pre> <p>Which, once the observer is unregistered, it gets nullified. The problem comes that, for some reason, in ICS it gets called twice. I think it's a bit silly to check for null parameters inside a <em>delete operation</em> as they do in the <code>Observable</code> class:</p> <pre><code>public void unregisterObserver(T observer) { // Android code if (observer == null) { throw new IllegalArgumentException("The observer is null."); } synchronized(mObservers) { int index = mObservers.indexOf(observer); if (index == -1) { throw new IllegalStateException("Observer " + observer + " was not registered."); } mObservers.remove(index); } } </code></pre> <p>Why don't they just ignore it ¬¬ They could just do this and would work as well (or better):</p> <pre><code>public void unregisterObserver(T observer) { // Android code synchronized(mObservers) { mObservers.remove(observer); } } </code></pre>
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      1. POWhat is triggering this Exception instance: "java.lang.IllegalArgumentException: The observer is null." and how could it be avoid?
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      1. POWhat is triggering this Exception instance: "java.lang.IllegalArgumentException: The observer is null." and how could it be avoid?
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    1. COcan you post your activity code and when you say returning to do you mean pressing the back button?
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    2. COYeah, by returning I mean pressing the back button. Here is the code for the activity (http://pastebin.com/68BzJcc1), but as I mention, there is non of my code shown in the stack.
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    3. COI've filled a bug report: http://code.google.com/p/android/issues/detail?id=22946 Although there must be a solution :/
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