android.support.v7.widget.RecyclerView.onInterceptTouchEvent中的NullPointerException

Question

我的oncreate看起来像：

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.layout_score);

    tbar = (android.support.v7.widget.Toolbar) findViewById(R.id.app_bar);
    setSupportActionBar(tbar);
    tabHost = (MaterialTabHost) this.findViewById(R.id.materialTabHost);
    pager = (ViewPager) this.findViewById(R.id.pager );

    // init view pager
    adapter = new CustomAdapter(getSupportFragmentManager());
    pager.setAdapter(adapter);
    pager.addOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
        @Override
        public void onPageSelected(int position) {
            // when user do a swipe the selected tab change
            tabHost.setSelectedNavigationItem(position);
        }
        @Override
        public void onPageScrolled(int arg0, float arg1, int arg2) {}

        @Override
        public void onPageScrollStateChanged(int state) {}
    });

    for (int i = 0; i < adapter.getCount(); i++) {
        tabHost.addTab(
                tabHost.newTab()
                        .setText(adapter.getPageTitle(i))
                        .setTabListener(this)
        );

    }
}

当我尝试在viewpager中滚动时，出现如下错误：

FATAL EXCEPTION: main
    java.lang.NullPointerException
            at android.support.v7.widget.RecyclerView.onInterceptTouchEvent(RecyclerView.java:1819)
            at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1839)
            at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2259)
            at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1922)
            at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2259) ....

任何帮助???