SwitchPreference null auf niedrigere sdk Version (api Ebene 21)

Question

OnFragmentInteractionListener mListener; 

    @Override 
public void onAttach(Context context) { 
    this.mContext = context; 
    super.onAttach(context); 
    if (context instanceof OnFragmentInteractionListener) { 
     mListener = (OnFragmentInteractionListener) context; 
    } else { 
     throw new RuntimeException(context.toString() + " must implement OnFragmentInteractionListener"); 
    } 
} 

ich kontinuierlich eine NPE erhalten, wenn ich, wenn einer meiner switchpreferences zu sehen versuche, wird geprüft, wie unten dargestellt:

switchPending = (SwitchPreference) getPreferenceManager().findPreference("pendingAlert"); 

stürzt auf dem nächste Zeile:

mListener.setSwitchPending(switchPending.isChecked()); 

Aber nur auf niedrigeren apis (im läuft mein Emulator bei v21). Warum ist das? Die komplette Spur ist dies:

java.lang.NullPointerException: Attempt to invoke interface method 'void com.maplesyrupindustries.j.airportmeet.SettingsFragment$OnFragmentInteractionListener.setSwitchPending(java.lang.Boolean)' on a null object reference 
                         at com.maplesyrupindustries.j.airportmeet.SettingsFragment.onCreateView(SettingsFragment.java:102) 
                         at android.app.Fragment.performCreateView(Fragment.java:2053) 
                         at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:894) 
                         at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067) 
                         at android.app.BackStackRecord.run(BackStackRecord.java:833) 
                         at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1452) 
                         at android.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:483) 
                         at android.support.v13.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:149) 
                         at android.support.v4.view.ViewPager.populate(ViewPager.java:1237) 
                         at android.support.v4.view.ViewPager.populate(ViewPager.java:1085) 
                         at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1611) 
                         at android.view.View.measure(View.java:17430) 
                         at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463) 
                         at android.support.design.widget.CoordinatorLayout.onMeasureChild(CoordinatorLayout.java:671) 
                         at android.support.design.widget.HeaderScrollingViewBehavior.onMeasureChild(HeaderScrollingViewBehavior.java:90) 
                         at android.support.design.widget.AppBarLayout$ScrollingViewBehavior.onMeasureChild(AppBarLayout.java:1319) 
                         at android.support.design.widget.CoordinatorLayout.onMeasure(CoordinatorLayout.java:736) 
                         at android.view.View.measure(View.java:17430) 
                         at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463) 
                         at android.widget.FrameLayout.onMeasure(FrameLayout.java:430) 
                         at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:135) 
                         at android.view.View.measure(View.java:17430) 
                         at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463) 
                         at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436) 
                         at android.widget.LinearLayout.measureVertical(LinearLayout.java:722) 
                         at android.widget.LinearLayout.onMeasure(LinearLayout.java:613) 
                         at android.view.View.measure(View.java:17430) 
                         at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463) 
                         at android.widget.FrameLayout.onMeasure(FrameLayout.java:430) 
                         at android.view.View.measure(View.java:17430) 
                         at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463) 
                         at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436) 
                         at android.widget.LinearLayout.measureVertical(LinearLayout.java:722) 
                         at android.widget.LinearLayout.onMeasure(LinearLayout.java:613) 
                         at android.view.View.measure(View.java:17430) 
                         at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463) 
                         at android.widget.FrameLayout.onMeasure(FrameLayout.java:430) 
                         at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2560) 
                         at android.view.View.measure(View.java:17430) 
                         at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2001) 
                         at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1166) 
                         at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1372) 
                         at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1054) 
                         at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5779) 
                         at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767) 
                         at android.view.Choreographer.doCallbacks(Choreographer.java:580) 
                         at android.view.Choreographer.doFrame(Choreographer.java:550) 
                         at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753) 
                         at android.os.Handler.handleCallback(Handler.java:739) 
                         at android.os.Handler.dispatchMessage(Handler.java:95) 
                         at android.os.Looper.loop(Looper.java:135) 
                         at android.app.ActivityThread.main(ActivityThread.java:5221) 
                         at java.lang.reflect.Method.invoke(Native Method) 
                        at java.lang.reflect.Method. 

Answer 1

ich das die veralteten (für sdk 23 und höher) onAttach Verfahren durch zwingende gelöst. So, jetzt habe ich 2 onAttach Methoden. Der für SDK < 23 verwendete ist wie folgt:

@SuppressWarnings("deprecation") 
@Override public void onAttach(Activity activity) { 
    super.onAttach(activity); 
    if (Build.VERSION.SDK_INT < 23) { 
     mContext = activity; 
     mListener = (OnFragmentInteractionListener) mContext; 
    } 
}