viewpager的一个错误

                                                                            java.lang.NullPointerException: Attempt to invoke virtual method 'android.os.Handler android.support.v4.app.FragmentHostCallback.getHandler()' on a null object reference
                                                                                at android.support.v4.app.FragmentManagerImpl.execSingleAction(FragmentManager.java:1623)
                                                                                at android.support.v4.app.BackStackRecord.commitNowAllowingStateLoss(BackStackRecord.java:637)
                                                                                at android.support.v4.app.FragmentStatePagerAdapter.finishUpdate(FragmentStatePagerAdapter.java:166)
                                                                                at android.support.v4.view.ViewPager.populate(ViewPager.java:1235)
                                                                                at android.support.v4.view.ViewPager.populate(ViewPager.java:1083)
                                                                                at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1609)
                                                                                at android.view.View.measure(View.java:20171)
                                                                                at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6330)
                                                                                at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1464)
                                                                                at android.widget.LinearLayout.measureVertical(LinearLayout.java:747)
                                                                                at android.widget.LinearLayout.onMeasure(LinearLayout.java:629)
                                                                                at android.view.View.measure(View.java:20171)
                                                                                at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:716)
                                                                                at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:462)
                                                                                at android.view.View.measure(View.java:20171)
                                                                                at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6330)
                                                                                at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
                                                                                at android.view.View.measure(View.java:20171)
                                                                                at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6330)
                                                                                at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1464)
                                                                                at android.widget.LinearLayout.measureVertical(LinearLayout.java:747)
                                                                                at android.widget.LinearLayout.onMeasure(LinearLayout.java:629)
                                                                                at android.view.View.measure(View.java:20171)
                                                                                at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6330)
                                                                                at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
                                                                                at com.android.internal.policy.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:3158)
                                                                                at android.view.View.measure(View.java:20171)
                                                                                at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1624)
                                                                                at android.view.View.measure(View.java:20171)
                                                                                at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:716)
                                                                                at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:462)
                                                                                at android.view.View.measure(View.java:20171)
                                                                                at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6330)
                                                                                at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
                                                                                at android.view.View.measure(View.java:20171)
                                                                                at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6330)
                                                                                at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1464)
                                                                                at android.widget.LinearLayout.measureVertical(LinearLayout.java:747)
                                                                                at android.widget.LinearLayout.onMeasure(LinearLayout.java:629)
                                                                                at android.view.View.measure(View.java:20171)
                                                                                at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6330)
                                                                                at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
                                                                                at com.android.internal.policy.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:3158)
                                                                                at android.view.View.measure(View.java:20171)
                                                                                at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2645)
                                                                                at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1600)
                                                                                at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1892)
                                                                                at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1488)
                                                                                at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:7451)
                                                                                at android.view.Choreographer$CallbackRecord.run(Choreographer.java:920)
                                                                                at android.view.Choreographer.doCallbacks(Choreographer.java:695)
                                                                                at android.view.Choreographer.doFrame(Choreographer.java:631)
                                                                                at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:906)
                                                                                at android.os.Handler.handleCallback(Handler.java:739)
                                                                                at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                                at android.os.Looper.loop(Looper.java:158)
                                                                                at android.app.ActivityThread.main(ActivityThread.java:7