问题描述
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}
@Overridepublic 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 */@Overridepublic 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 }}@Overridepublic void onPageSelected(int position) {}@Overridepublic 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ViewPagerprivate void initPager() { list = new ArrayList<Fragment>(); mFirstFragment = new FirstFragment(); mSecondFragment = new SecondFragment(); mThirdFragment = new ThirdFragment(); list.add(mFirstFragment); list.add(mSecondFragment); list.add(mThirdFragment);}
}
问题解答
回答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
