Android中 Fragment + ViewPager 做出更具现代感的交互

public class MyFragment extends Fragment {
 @Override
 public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
  return inflater.inflate(R.layout.fragement_recommend, container, false);
 }
}
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<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recommend_list"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="#FFF4F4F4"
        android:overScrollMode="never" />

</RelativeLayout>
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/**
 * @author JonesYang
 * @Data 2020-10-17
 * @Function 创建Fragment
 */
public class FragmentCreator {
 //代表这不同的工厂类型
    public static final int INDEX_RECOMMEND = 0;
    public static final int INDEX_SUBSCRIPTION = 1;
    public static final int INDEX_HISTORY = 2;
    // Fragment 的数量
    public static final int PAGE_COUNT = 3;
    //使用一个 Map 集合把 Fragment 缓存起来
    private static Map<Integer, BaseFragment> sCache = new HashMap<>();
    //获取 Fragment 的方法
    public static BaseFragment getFragment(int index) {
        //先在缓存中查找，如果缓存中存在就返回对应的 Fragment
        BaseFragment fragment = sCache.get(index);
        if (fragment != null) {
            return fragment;
        }

        //如果缓存不存在相应的 Fragment
        switch (index) {
            case INDEX_RECOMMEND:
                fragment = new RecommendFragment();
                break;
            case INDEX_SUBSCRIPTION:
                fragment = new SubscriptionFragment();
                break;
            case INDEX_HISTORY:
                fragment = new HistoryFragment();
                break;
        }
        //把创建的 Fragment 加入到 Map 缓存中
        sCache.put(index, fragment);
        return fragment;
    }
}
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/**
 * @author JonesYang
 * @Data 2020-10-17
 * @Function  ViewPager + Fragment 的适配器
 */
public class MainContentAdapter extends FragmentPagerAdapter {

    public MainContentAdapter(FragmentManager manager) {
        super(manager);
    }

    @NonNull
    @Override
    public Fragment getItem(int position) {
        //返回 获取到的 Fragment
        return FragmentCreator.getFragment(position);
    }

    @Override
    public int getCount() {
        //返回 Fragment 的数量
        return FragmentCreator.PAGE_COUNT;
    }
}
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    <androidx.viewpager.widget.ViewPager
        android:id="@+id/content_pager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_below="@+id/magic_indicator"
        android:overScrollMode="never" />
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 //获取 ViewPager 控件的 ID
        viewPager = findViewById(R.id.content_pager);
     // 获取 FragmentManager
        FragmentManager fragmentManager = getSupportFragmentManager();
     //定义适配器，参数为 FragmentManager
        MainContentAdapter contentAdapter = new MainContentAdapter(manager);
        // 为 ViewPager 设置适配器
        viewPager.setAdapter(contentAdapter);
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 viewPager.setCurrentItem(int position); //只需要把 Fragment 的 position 传进来
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    public interface OnPageChangeListener {

        /**
         * This method will be invoked when the current page is scrolled, either as part
         * of a programmatically initiated smooth scroll or a user initiated touch scroll.
         *
         * @param position Position index of the first page currently being displayed.
         *                 Page position+1 will be visible if positionOffset is nonzero.
         * @param positionOffset Value from [0, 1) indicating the offset from the page at position.
         * @param positionOffsetPixels Value in pixels indicating the offset from position.
         */
        void onPageScrolled(int position, float positionOffset, @Px int positionOffsetPixels);

        /**
         * This method will be invoked when a new page becomes selected. Animation is not
         * necessarily complete.
         *
         * @param position Position index of the new selected page.
         */
        void onPageSelected(int position);

        /**
         * Called when the scroll state changes. Useful for discovering when the user
         * begins dragging, when the pager is automatically settling to the current page,
         * or when it is fully stopped/idle.
         *
         * @param state The new scroll state.
         * @see ViewPager#SCROLL_STATE_IDLE
         * @see ViewPager#SCROLL_STATE_DRAGGING
         * @see ViewPager#SCROLL_STATE_SETTLING
         */
        void onPageScrollStateChanged(int state);
    }
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