Recyclerview slide appears null pointer exception

<span style= "FONT-SIZE:24PX;" ><strong> Exception Information:</strong></span>

05-07 14:29:49.924:e/messagequeue-jni (16160): java.lang.nullpointerexception05-07 14:29:49.924:e/messagequeue-jni (16160): at Android.support.v7.widget.RecyclerView.computeVerticalScrollOffset (recyclerview.java:1613) 05-07 14:29:49.924:e/messagequeue-jni (16160): at android.view.View.canScrollVertically (view.java:11380) 05-07 14:29:49.924:e/messagequeue-jni (16160): at Android.support.v4.view.ViewCompatICS.canScrollVertically ( viewcompatics.java:35) 05-07 14:29:49.924:e/messagequeue-jni (16160): at android.support.v4.view.viewcompat$ Icsviewcompatimpl.canscrollvertically (viewcompat.java:1253) 05-07 14:29:49.924:e/messagequeue-jni (16160): at Android.support.v4.view.ViewCompat.canScrollVertically (viewcompat.java:1695) 05-07 14:29:49.924:e/ Messagequeue-jni (16160): at Android.support.v4.widget.SwipeRefreshLayout.canChildScrollUp ( swiperefreshlayout.java:646) 05-07 14:29:49.924:e/messagequeue-jni (16160): at Android.support.v4.widget.SwipeRefreshLayout.onInterceptTouchEvent (Swiperefreshlayout.java:660) 05-07 14:29:49.924:e/messagequeue-jni (16160): at Android.view.ViewGroup.dispatchTouchEvent (Viewgroup.java : 1827) 05-07 14:29:49.924:e/messagequeue-jni (16160): at Android.view.ViewGroup.dispatchTransformedTouchEvent ( viewgroup.java:2241) 05-07 14:29:49.924:e/messagequeue-jni (16160): at Android.view.ViewGroup.dispatchTouchEvent ( viewgroup.java:1904) 05-07 14:29:49.924:e/messagequeue-jni (16160): at Android.view.ViewGroup.dispatchTransformedTouchEvent (viewgroup.java:2241) 05-07 14:29:49.924:e/messagequeue-jni ( 16160): At Android.view.ViewGroup.dispatchTouchEvent (viewgroup.java:1904) 05-07 14:29:49.924:e/messagequeue-jni ( 16160): At Android.view.ViewGroup.dispatchTransformedTouchEvent (viewgroup.java:2241) 05-07 14:29:49.924:e/ Messagequeue-jni (16160): at Android.view.ViewGroup.dispatchTouchEvent (viewgroup.java:1904) 05-07 14:29:49.924:e/ Messagequeue-jni (16160): at Android.view.ViewGroup.dispatchTransformedTouchEvent (viewgroup.java:2241) 05-07 14:29:49.924:e/messagequeue-jni (16160): at AndroidOid.view.ViewGroup.dispatchTouchEvent (viewgroup.java:1904) 05-07 14:29:49.924:e/messagequeue-jni (16160): at Android.view.ViewGroup.dispatchTransformedTouchEvent (viewgroup.java:2241) 05-07 14:29:49.924:e/messagequeue-jni ( 16160): At Android.view.ViewGroup.dispatchTouchEvent (viewgroup.java:1904) 05-07 14:29:49.924:e/messagequeue-jni ( 16160): At Android.view.ViewGroup.dispatchTransformedTouchEvent (viewgroup.java:2241) 05-07 14:29:49.924:e/ Messagequeue-jni (16160): at Android.view.ViewGroup.dispatchTouchEvent (viewgroup.java:1904) 05-07 14:29:49.924:e/ Messagequeue-jni (16160): at Com.android.internal.policy.impl.phonewindow$decorview.superdispatchtouchevent ( phonewindow.java:1968) 05-07 14:29:49.924:e/messagequeue-jni (16160): at Com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent (phonewindow.java:1420) 05-07 14:29:49.924:e /messagequeue-jni (16160): at Android.app.Activity.dispatchTouchEvent (activity.java:2428) 05-07 14:29:49.924:e/ Messagequeue-jni (16160): at ANDROID.SUPPORT.V7.VIew. Windowcallbackwrapper.dispatchtouchevent (windowcallbackwrapper.java:60) 05-07 14:29:49.924:e/messagequeue-jni ( 16160): At Android.support.v7.view.WindowCallbackWrapper.dispatchTouchEvent (windowcallbackwrapper.java:60) 05-07 14:29:49.924:e/messagequeue-jni (16160): at com.android.internal.policy.impl.phonewindow$ Decorview.dispatchtouchevent (phonewindow.java:1916) 05-07 14:29:49.924:e/messagequeue-jni (16160): at Android.view.View.dispatchPointerEvent (view.java:7437) 05-07 14:29:49.924:e/messagequeue-jni (16160): at Android.view.ViewRootImpl.deliverPointerEvent (viewrootimpl.java:3610) 05-07 14:29:49.924:e/messagequeue-jni ( 16160): At Android.view.ViewRootImpl.deliverInputEvent (viewrootimpl.java:3538) 05-07 14:29:49.924:e/ Messagequeue-jni (16160): at Android.view.ViewRootImpl.doProcessInputEvents (viewrootimpl.java:4790) 05-07 14:29:49.924:e/messagequeue-jni (16160): at Android.view.ViewRootImpl.enqueueInputEvent (viewrootimpl.java:4750) 05-07 14:29:49.924:e/messagequeue-jni (16160): at Android.View. Viewrootimpl$windowinputeventreceiver.oninputevent (viewrootimpl.java:4902) 05-07 14:29:49.924:e/messagequeue-jni (16160): at Android.view.InputEventReceiver.dispatchInputEvent (inputeventreceiver.java:179) 05-07 14:29:49.924:e/ Messagequeue-jni (16160): at Android.os.MessageQueue.nativePollOnce (Native Method) 05-07 14:29:49.924:e/ Messagequeue-jni (16160): at Android.os.MessageQueue.next (messagequeue.java:125) 05-07 14:29:49.924:e/ Messagequeue-jni (16160): at Android.os.Looper.loop (looper.java:140) 05-07 14:29:49.924:e/messagequeue-jni (16160): At Android.app.ActivityThread.main (activitythread.java:5297) 05-07 14:29:49.924:e/messagequeue-jni (16160): at Java.lang.reflect.Method.invokeNative (Native Method) 05-07 14:29:49.924:e/messagequeue-jni (16160): at Java.lang.reflect.Method.invoke (method.java:511) 05-07 14:29:49.924:e/messagequeue-jni (16160): at Com.android.internal.os.zygoteinit$methodandargscaller.run (zygoteinit.java:833) 05-07 14:29:49.924:e/ Messagequeue-jni (16160): at COM.ANDROID.INternal.os.ZygoteInit.main (zygoteinit.java:600) 05-07 14:29:49.924:e/messagequeue-jni (16160): at Dalvik.system.NativeStart.main (Native Method) 05-07 14:29:49.930:e/androidruntime (16160): FATAL exception:main05-07 14:29:49.930:e/androidruntime (16160): java.lang.nullpointerexception05-07 14:29:49.930:e/androidruntime (16160): At Android.support.v7.widget.RecyclerView.computeVerticalScrollOffset (recyclerview.java:1613) 05-07 14:29:49.930: E/androidruntime (16160): at android.view.View.canScrollVertically (view.java:11380) 05-07 14:29:49.930:e/ Androidruntime (16160): at android.support.v4.view.ViewCompatICS.canScrollVertically (viewcompatics.java:35) 05-07 14:29:49.930:e/androidruntime (16160): at android.support.v4.view.viewcompat$ Icsviewcompatimpl.canscrollvertically (viewcompat.java:1253) 05-07 14:29:49.930:e/androidruntime (16160): at Android.support.v4.view.ViewCompat.canScrollVertically (viewcompat.java:1695) 05-07 14:29:49.930:e/androidruntime (16160): at ANDROID.SUPPORT.V4.WIDGET.SWIPEREFREshlayout.canchildscrollup (swiperefreshlayout.java:646) 05-07 14:29:49.930:e/androidruntime (16160): at Android.support.v4.widget.SwipeRefreshLayout.onInterceptTouchEvent (swiperefreshlayout.java:660) 05-07 14:29:49.930:e/androidruntime (16160): at Android.view.ViewGroup.dispatchTouchEvent (viewgroup.java:1827) 05-07 14:29:49.930:e/androidruntime (16160): at Android.view.ViewGroup.dispatchTransformedTouchEvent (Viewgroup.java : 2241) 05-07 14:29:49.930:e/androidruntime (16160): at Android.view.ViewGroup.dispatchTouchEvent (Viewgroup.java : 1904) 05-07 14:29:49.930:e/androidruntime (16160): at Android.view.ViewGroup.dispatchTransformedTouchEvent ( viewgroup.java:2241) 05-07 14:29:49.930:e/androidruntime (16160): at Android.view.ViewGroup.dispatchTouchEvent ( viewgroup.java:1904) 05-07 14:29:49.930:e/androidruntime (16160): at Android.view.ViewGroup.dispatchTransformedTouchEvent (viewgroup.java:2241) 05-07 14:29:49.930:e/androidruntime ( 16160): at Android.view.ViewGroup.dispatchTouchEvent (viewgroup.java:1904) 05-07 14:29:49.930:e/androidruntime (16160): at Android.view.ViewGroup.dispatchTransformedTouchEvent ( viewgroup.java:2241) 05-07 14:29:49.930:e/androidruntime (16160): at Android.view.ViewGroup.dispatchTouchEvent ( viewgroup.java:1904) 05-07 14:29:49.930:e/androidruntime (16160): at Android.view.ViewGroup.dispatchTransformedTouchEvent (viewgroup.java:2241) 05-07 14:29:49.930:e/androidruntime ( 16160): At Android.view.ViewGroup.dispatchTouchEvent (viewgroup.java:1904) 05-07 14:29:49.930:e/androidruntime ( 16160): At Android.view.ViewGroup.dispatchTransformedTouchEvent (viewgroup.java:2241) 05-07 14:29:49.930:e/ Androidruntime (16160): at Android.view.ViewGroup.dispatchTouchEvent (viewgroup.java:1904) 05-07 14:29:49.930:e/ Androidruntime (16160): at Com.android.internal.policy.impl.phonewindow$decorview.superdispatchtouchevent ( phonewindow.java:1968) 05-07 14:29:49.930:e/androidruntime (16160): at Com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent (phonewindow.java:1420) 05-07 14:29:49.930: E/androidruntime (16160): at Android.app.Activity.dispatchTouchEvent (activity.java:2428) 05-07 14:29:49.930:e/ Androidruntime (16160): at Android.support.v7.view.WindowCallbackWrapper.dispatchTouchEvent ( WINDOWCALLBACKWRAPPER.JAVA:60) 05-07 14:29:49.930:e/androidruntime (16160): at Android.support.v7.view.WindowCallbackWrapper.dispatchTouchEvent (windowcallbackwrapper.java:60) 05-07 14:29:49.930:e/androidruntime (16160): at com.android.internal.policy.impl.phonewindow$ Decorview.dispatchtouchevent (phonewindow.java:1916) 05-07 14:29:49.930:e/androidruntime (16160): at Android.view.View.dispatchPointerEvent (view.java:7437) 05-07 14:29:49.930:e/androidruntime (16160): at Android.view.ViewRootImpl.deliverPointerEvent (viewrootimpl.java:3610) 05-07 14:29:49.930:e/androidruntime (16160) : At Android.view.ViewRootImpl.deliverInputEvent (viewrootimpl.java:3538) 05-07 14:29:49.930:e/androidruntime (16160 ): At Android.view.ViewRootImpl.doProcessInputEvents (viewrootimpl.java:4790) 05-07 14:29:49.930:e/androidRuntime (16160): at Android.view.ViewRootImpl.enqueueInputEvent (viewrootimpl.java:4750) 05-07 14:29:49.930:e/ Androidruntime (16160): at Android.view.viewrootimpl$windowinputeventreceiver.oninputevent (ViewRootImpl.java:4902 ) 05-07 14:29:49.930:e/androidruntime (16160): at Android.view.InputEventReceiver.dispatchInputEvent ( inputeventreceiver.java:179) 05-07 14:29:49.930:e/androidruntime (16160): at Android.os.MessageQueue.nativePollOnce (Native Method) 05-07 14:29:49.930:e/androidruntime (16160): at Android.os.MessageQueue.next (messagequeue.java:125) 05-07 14:29:49.930:e/androidruntime (16160): at Android.os.Looper.loop (looper.java:140) 05-07 14:29:49.930:e/ Androidruntime (16160): at Android.app.ActivityThread.main (activitythread.java:5297) 05-07 14:29:49.930:e/ Androidruntime (16160): at Java.lang.reflect.Method.invokeNative (Native Method) 05-07 14:29:49.930:e/androidruntime ( 16160): At Java.lang.reflect.Method.invoke (method.java:511) 05-07 14:29:49.930:e/androidruntime (16160): at Com.android.inteRnal.os.zygoteinit$methodandargscaller.run (zygoteinit.java:833) 05-07 14:29:49.930:e/androidruntime (16160): at Com.android.internal.os.ZygoteInit.main (zygoteinit.java:600) 05-07 14:29:49.930:e/androidruntime (16160): at Dalvik.system.NativeStart.main (Native Method) 05-07 14:29:50.048:e/apperrordialog (2309): Failed to get Ilowstoragehandle instance05-07 14:29:50.305:e/aee/dumpstate (16293): Copy_process:execv/system/xbin/showmap failed (2), No such file or directory05-07 14:29:50.867:e/aee/dumpstate (16291): Copy_file:copy/proc/gpulog to Sys_gpu_info FAI LED (2), No such file or directory05-07 14:29:52.425:e/aee/dumpstate (16303): Copy_process:execv/system/xbin/procrank FA Iled (2), No such file or directory05-07 14:29:53.023:e/aee/dumpstate (16291): Copy_file:copy/proc/slabinfo to SYS_SLAB_I NFO failed (2), No such file or directory05-07 14:29:53.113:e/aee/dumpstate (16291): Copy_file:copy/sys/kernel/debug/wak Eup_sources to Sys_kernel_wakelocks failed (2), No such file or directory

Courseactivity.java

private void Initview () {... Recyclerview = (Recyclerview) Findviewbyid (r.id.rv_activity_course); Presenter.initcourseslist ();} @Overridepublic void Initcourseslist (list<course> courses) {    adapter = new commonrecyclerviewadapter< Course> (this, r.layout.item_activity_course, courses) {        @Override public        void Convert ( Commondrecyclerviewholder holder, Course Course) {            //...        }    };    Recyclerview.setlayoutmanager (New Linearlayoutmanager (this));    Key point    recyclerview.sethasfixedsize (true);    Recyclerview.setadapter (adapter);}

the key to the error is : Reclerview when initializing the data because of the time-consuming operation, and the layout manager is behind the time-consuming operation, resulting in the process of data loading, the layout manager has not been set, the slide reclerview will report null pointer error. 
The solution is also very simple,  Set the layout manager right after Findviewbyid.  , namely:
= (Recyclerview) Findviewbyid (r.id.  Rv_activity_course);
Recyclerview. Setlayoutmanager (linearlayoutmanager (this));    Key points
。。。。。。 And do other things.

Recyclerview slide appears null pointer exception