android - 在fragment中管理fragment

Question

小弟打算在fragment中使用ViewPager，但是在创建适配器时总是为null
MyPagerAdapter adapter = new MyPagerAdapter(getChildFragmentManager());
在Activity中管理类fragment和Fragment中管理有什么区别呢？还请高人指点！以下是我的一部分代码
public class CommunicationFragment extends Fragment {

private ViewPager viewPager;
private TextView tvLine;
private LayoutParams layoutParams;
private List<Fragment> list;

private FirstFragment mFirstFragment;
private SecondFragment mSecondFragment;
private ThirdFragment mThirdFragment;

public CommunicationFragment() {
    // Required empty public constructor
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    View view = inflater.inflate(R.layout.fragment_communication, container, false);
    tvLine = (TextView)view.findViewById(R.id.tvLine);

    // 获取line的长度 获取手机屏幕的宽度
    int width = getActivity().getWindowManager().getDefaultDisplay().getWidth();
    int lineWidth = width / 3;
    // 得到tvLine参数类,参数类中包含tvLine的width,height,gravity等属性
    layoutParams = (LayoutParams) tvLine.getLayoutParams();
    // 把屏幕宽度赋值给layoutParams.width,不要写反了
    layoutParams.width = lineWidth;
    // 黑条的长度就是屏幕的1/3了
    tvLine.setLayoutParams(layoutParams);

    // 初始化ViewPager的集合
    initPager();

    // 创建适配器
    MyPagerAdapter adapter = new MyPagerAdapter(getActivity().getSupportFragmentManager());
    // 给ViewPager设置适配器
    viewPager.setAdapter(adapter);
    // 给ViewPager设置监听事件
    viewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
        /**
         * position:position当前ViewPager的索引值 positionOffset:表示当前Pager偏移的百分比 positionOffsetPixels:偏移了多少像素
         */
        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
            // 获取tvLine的左边距
            layoutParams = (LayoutParams) tvLine.getLayoutParams();
            // 说明它有偏移了
            if (layoutParams != null && positionOffset != 0) {
                layoutParams.leftMargin = (int) ((position + positionOffset) * layoutParams.width);
                tvLine.setLayoutParams(layoutParams);// 具有新的layoutMargin的layoutParams
            }
        }

        @Override
        public void onPageSelected(int position) {

        }

        @Override
        public void onPageScrollStateChanged(int state) {

        }
    });

    return view;
}

//设置适配器
class MyPagerAdapter extends FragmentPagerAdapter {

    public MyPagerAdapter(FragmentManager fm) {
        super(fm);

    }

    @Override
    public Fragment getItem(int arg0) {

        return list.get(arg0);
    }

    @Override
    public int getCount() {

        return list.size();
    }

}
//初始化ViewPager
private void initPager() {
    list = new ArrayList<Fragment>();

    mFirstFragment = new FirstFragment();
    mSecondFragment = new SecondFragment();
    mThirdFragment = new ThirdFragment();

    list.add(mFirstFragment);
    list.add(mSecondFragment);
    list.add(mThirdFragment);
}

}

Answer 1

在 Fragment 中，使用这个方法获取 FragmentManager

Fragment#getChildFragmentManager()

Fragment 内部有一个 mChildFragmentManager 实例，这个实例才是管理 内部包含的 fragment 的 FragmentManager