SlidingTab片段

Question

我正在尝试在片段中添加滑动选项卡。这是标签布局

<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:background="?attr/colorPrimaryDark" />

        <com.example.materialdrawerfragment.SlidingTabLayout
                android:id="@+id/sliding_tabs"
                android:background="?attr/colorPrimaryDark"
                android:layout_width="match_parent"
                android:layout_height="wrap_content" />

            <android.support.v4.view.ViewPager
                android:id="@+id/pager"
                android:layout_width="match_parent"
                android:layout_height="0px"
                android:layout_weight="1"
                android:background="@android:color/white" />
        </LinearLayout>

和Fragment类，

 public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

        View v = inflater.inflate(R.layout.fragment_cont, container, false);

         pager = (ViewPager) getActivity().findViewById(R.id.viewpager);
         slidingTabLayout = (SlidingTabLayout) getActivity().findViewById(R.id.sliding_tabs);
         pager.setAdapter(new ViewPagerAdapter(getActivity().getSupportFragmentManager(), titles));

         slidingTabLayout.setViewPager(pager);
        return v;
    }

我得到的错误是，

04-11 00:40:31.759: E/AndroidRuntime(11107): FATAL EXCEPTION: main
04-11 00:40:31.759: E/AndroidRuntime(11107): java.lang.NullPointerException
04-11 00:40:31.759: E/AndroidRuntime(11107):    at com.example.materialdrawerfragment.MyFragment.onCreateView(MyFragment.java:54)
04-11 00:40:31.759: E/AndroidRuntime(11107):    at android.support.v4.app.Fragment.performCreateView(Fragment.java:1786)
04-11 00:40:31.759: E/AndroidRuntime(11107):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:953)
04-11 00:40:31.759: E/AndroidRuntime(11107):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1136)
04-11 00:40:31.759: E/AndroidRuntime(11107):    at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:739)
04-11 00:40:31.759: E/AndroidRuntime(11107):    at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1499)
04-11 00:40:31.759: E/AndroidRuntime(11107):    at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:456)
04-11 00:40:31.759: E/AndroidRuntime(11107):    at android.os.Handler.handleCallback(Handler.java:615)
04-11 00:40:31.759: E/AndroidRuntime(11107):    at android.os.Handler.dispatchMessage(Handler.java:92)
04-11 00:40:31.759: E/AndroidRuntime(11107):    at android.os.Looper.loop(Looper.java:137)
04-11 00:40:31.759: E/AndroidRuntime(11107):    at android.app.ActivityThread.main(ActivityThread.java:4931)
04-11 00:40:31.759: E/AndroidRuntime(11107):    at java.lang.reflect.Method.invokeNative(Native Method)
04-11 00:40:31.759: E/AndroidRuntime(11107):    at java.lang.reflect.Method.invoke(Method.java:511)
04-11 00:40:31.759: E/AndroidRuntime(11107):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:791)
04-11 00:40:31.759: E/AndroidRuntime(11107):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:558)
04-11 00:40:31.759: E/AndroidRuntime(11107):    at dalvik.system.NativeStart.main(Native Method)