Android viewpager里面嵌套使用listview也许ExpandableList时，在移出子view时报IllegalArgumentExcept

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? ? log如下：

06-22 23:45:50.110: E/ActivityThread(6217): Don't dump hprof file because it is not in monkey test! false, false06-22 23:45:50.120: E/AndroidRuntime(6217): FATAL EXCEPTION: main06-22 23:45:50.120: E/AndroidRuntime(6217): java.lang.IllegalArgumentException: The observer is null.06-22 23:45:50.120: E/AndroidRuntime(6217): 	at android.database.Observable.unregisterObserver(Observable.java:59)06-22 23:45:50.120: E/AndroidRuntime(6217): 	at android.widget.BaseAdapter.unregisterDataSetObserver(BaseAdapter.java:42)06-22 23:45:50.120: E/AndroidRuntime(6217): 	at android.widget.AbsListView.onDetachedFromWindow(AbsListView.java:2373)06-22 23:45:50.120: E/AndroidRuntime(6217): 	at android.view.View.dispatchDetachedFromWindow(View.java:9818)06-22 23:45:50.120: E/AndroidRuntime(6217): 	at android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:2283)06-22 23:45:50.120: E/AndroidRuntime(6217): 	at android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:2281)06-22 23:45:50.120: E/AndroidRuntime(6217): 	at android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:2281)06-22 23:45:50.120: E/AndroidRuntime(6217): 	at android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:2281)06-22 23:45:50.120: E/AndroidRuntime(6217): 	at android.view.ViewGroup.removeViewInternal(ViewGroup.java:3601)06-22 23:45:50.120: E/AndroidRuntime(6217): 	at android.view.ViewGroup.removeViewInternal(ViewGroup.java:3581)06-22 23:45:50.120: E/AndroidRuntime(6217): 	at android.view.ViewGroup.removeView(ViewGroup.java:3529)06-22 23:45:50.120: E/AndroidRuntime(6217): 	at android.support.v4.view.ViewPager.removeView(ViewPager.java:1321)06-22 23:45:50.120: E/AndroidRuntime(6217): 	at com.jeejen.largecalendar.ui.YiJiAct$YiJiPagerAdapter.destroyItem(YiJiAct.java:176)06-22 23:45:50.120: E/AndroidRuntime(6217): 	at android.support.v4.view.ViewPager.populate(ViewPager.java:1036)06-22 23:45:50.120: E/AndroidRuntime(6217): 	at android.support.v4.view.ViewPager.populate(ViewPager.java:914)06-22 23:45:50.120: E/AndroidRuntime(6217): 	at android.support.v4.view.ViewPager$3.run(ViewPager.java:244)

? ?Android viewpager里面嵌套使用listview或者ExpandableList时，在移出子view时报IllegalArgumentExcept；

? ?这个是因为4.0系统对viewpage的兼容问题导致的，因为viewpager在移除listview或者expandableList时会调用一次listview（expandableList）的unregisterDataSetObserver方法，而listview（expandableList）本身也会调用这个方法，解决方法就是复写adapter的unregisterDataSetObserver方法，判断一下如果observer是null就不执行了：

	@Override		public void unregisterDataSetObserver(DataSetObserver observer) {			if(observer != null)				super.unregisterDataSetObserver(observer);		}

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