java.lang.NullPointerException

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  • RecyclerView - Alternating layouts
    via Stack Overflow by user1754499
    ,
    • java.lang.NullPointerException: Attempt to invoke virtual method 'android.support.v7.widget.RecyclerView$LayoutManager android.support.v7.widget.RecyclerView.getLayoutManager()' on a null object reference at com.example.wsdw.MainActivity.onOptionsItemSelected(MainActivity.java:50) at android.app.Activity.onMenuItemSelected(Activity.java:2908) at android.support.v4.app.FragmentActivity.onMenuItemSelected(FragmentActivity.java:406) at android.support.v7.app.AppCompatActivity.onMenuItemSelected(AppCompatActivity.java:195) at android.support.v7.view.WindowCallbackWrapper.onMenuItemSelected(WindowCallbackWrapper.java:103) at android.support.v7.app.AppCompatDelegateImplV9.onMenuItemSelected(AppCompatDelegateImplV9.java:667) at android.support.v7.view.menu.MenuBuilder.dispatchMenuItemSelected(MenuBuilder.java:810) at android.support.v7.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:152) at android.support.v7.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:957) at android.support.v7.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:947) at android.support.v7.widget.ActionMenuView.invokeItem(ActionMenuView.java:616) at android.support.v7.view.menu.ActionMenuItemView.onClick(ActionMenuItemView.java:153) at android.view.View.performClick(View.java:5198) at android.view.View$PerformClick.run(View.java:21147) at android.os.Handler.handleCallback(Handler.java:739) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:148) at android.app.ActivityThread.main(ActivityThread.java:5417) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
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