关于在fragment中取得layoutinflater的问题

我在用viewpage嵌套fragment的时候在fragment中取得layoutinflater，报空指针异常，调试的时候activity和layoutInflater都有值，然后就全为空了，代码如下：

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

        rootView = inflater.inflate(R.layout.fragment_business_base_order, container, false);
        activity = getActivity();
        initView();
        return rootView;
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        layoutInflater = (LayoutInflater) activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        loadingData();
    }

然后，我稍微修改了一下，问题就解决了，代码如下：

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

        rootView = inflater.inflate(R.layout.fragment_business_base_order, container, false);
        activity = getActivity();
       initView();
        return rootView;
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        layoutInflater = getLayoutInflater(savedInstanceState);
        loadingData();
    }

所以我就感觉很疑惑，为什么第二种方法可以而第一种不可以，我又修改了一下代码，结果也是可以运行的，代码如下：

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

        rootView = inflater.inflate(R.layout.fragment_business_base_order, container, false);
        activity = getActivity();
        layoutInflater = (LayoutInflater) activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        initView();
        return rootView;
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        loadingData();
    }