循环使用FragmentPagerAdapter

3

我有一个FragmentPagerAdapter,它的工作方式正常,但是我想知道如果FragmentPagerAdapter在最后一页,如何使其循环回到第一页并像正常情况一样继续进行。

这是我正在使用的示例代码:

public class FragmentPager extends FragmentActivity {
MyAdapter mAdapter;
ViewPager mPager;
static final int NUM_ITEMS = 5;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    mAdapter = new MyAdapter(getSupportFragmentManager());

    mPager = (ViewPager)findViewById(R.id.pager);
    mPager.setAdapter(mAdapter);
}

public static class MyAdapter extends FragmentPagerAdapter {
    public MyAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public int getCount() {
        return NUM_ITEMS;
    }

    @Override
    public Fragment getItem(int position) {
        return MyFragment.newInstance(position);
    }
}

public static class MyFragment extends ListFragment{
    int mNum;

    /**
     * Create a new instance of CountingFragment, providing "num"
     * as an argument.
     */
    static MyFragment newInstance(int num) {
        MyFragment f = new MyFragment();

        // Supply num input as an argument.
        Bundle args = new Bundle();
        args.putInt("num", num);
        f.setArguments(args);

        return f;
    }

    /**
     * When creating, retrieve this instance's number from its arguments.
     */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mNum = getArguments() != null ? getArguments().getInt("num") : 1;
    }

    /**
     * The Fragment's UI is just a simple text view showing its
     * instance number.
     */
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.fragment_pager_list, container, false);
        View tv = v.findViewById(R.id.text);
        ((TextView)tv).setText("Fragment #" + mNum);
        return v;
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        setListAdapter(new ArrayAdapter<String>(getActivity(),
                android.R.layout.simple_list_item_1, new String[] {"test1","test2","test3","test4","Test5"}));
    }

    @Override
    public void onListItemClick(ListView l, View v, int position, long id) {
        Log.i("FragmentList", "Item clicked: " + id);
    }
}

}

基本上当它到达最后一个片段时,我该如何让它显示第一个片段,就像它会去任何其他片段一样?
例如:A->BB->CC->A 和反向 A->CC->BB->A
3个回答

3

这是我的解决方案,我有“ n”个屏幕(在此示例中为5),因为我希望在列表末尾返回到第一个屏幕,所以我“添加另一个屏幕”,它只是上一个屏幕的精确副本,并对反向方向执行相同的操作。基本上,我现在有“ n”个屏幕+ 2(在此示例中为7)。屏幕设置如下:C的副本ABCA的副本,然后我设置手势监听器来监视特定页面的滑动。

如果在列表末尾(“ A的副本”)并检测到向左大于某个像素数的滑动,则移动到页面A并继续在正常页面旋转中向后滑动。

向相反方向滑动也是同样的道理。

问题

从一端页面移到另一端页面以模拟循环时,速度会变慢,因为 ViewPager 加载当前页面之前和之后的页面,但由于您位于页面列表的末尾或开头,它不会像通常那样加载下一页,因为技术上没有下一页。这只会在每个列表行具有复杂自定义视图时才会发生。

您无法将其与页面滚动的动画一起使用,因为它看起来不连续,并且在从复制的页面到实际页面移动时(即从A的副本到A时)会进行动画处理。

此外,它有时似乎会卡在页面末尾,我不知道为什么

这是我基于Android开发者网站上的viewpager示例的完整演示应用程序

public class FragmentPager extends FragmentActivity{
MyAdapter mAdapter;
public static ViewPager mPager;
static int currentPage = 1;
static final int NUM_ITEMS = 7;
public static View vContainer;
float dxInitial=0;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    mAdapter = new MyAdapter(getSupportFragmentManager());

    mPager = (ViewPager)findViewById(R.id.pager);
    mPager.setAdapter(mAdapter);
    mPager.setCurrentItem(1,false);

    mPager.setOnTouchListener(new OnTouchListener(){

        @Override
        public boolean onTouch(View v, MotionEvent event) {


            if(event.getAction() == MotionEvent.ACTION_DOWN){
                dxInitial=event.getX();
                Log.d("INITIAL X", String.valueOf(dxInitial));
            }else if(event.getAction() == MotionEvent.ACTION_MOVE){
                if(event.getX() - dxInitial > 100 && currentPage==1){
                    mPager.setCurrentItem(6,false);
                }else if(dxInitial - event.getX() > 100 && currentPage==5){
                    mPager.setCurrentItem(0,false);
                }else if(dxInitial - event.getX() > 50 && currentPage==6){
                    mPager.setCurrentItem(1,false);
                }else if(event.getX() - dxInitial > 50 && currentPage==0){
                    mPager.setCurrentItem(5,false);
                }
            }

            /*if(Math.abs(dx) > Math.abs(dy)) {
                if(dx>75){ directiion = "right";
                }else if{
                    direction = "left";
                }
            } else {
                if(dy>0) direction = "down";
                else direction = "up";
            }*/

            return false;
        }

    });
    mPager.setOnPageChangeListener(new OnPageChangeListener(){

        @Override
        public void onPageScrollStateChanged(int state) {
            // TODO Auto-generated method stub
            if(state == ViewPager.SCROLL_STATE_IDLE){

            }
        }

        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

        }

        @Override
        public void onPageSelected(int arg0) {
            currentPage=arg0;

        }

    });
}

public static class MyAdapter extends FragmentPagerAdapter{
    public MyAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public int getCount() {
        return NUM_ITEMS;
    }

    @Override
    public Fragment getItem(int position) {
        return MyFragment.newInstance(position);
    }

    @Override
    public Object instantiateItem(View container, int position) {
        vContainer=container;
        return super.instantiateItem(container, position);

    }
}

public static class MyFragment extends ListFragment{
    int mNum;

    /**
     * Create a new instance of CountingFragment, providing "num"
     * as an argument.
     */
    static MyFragment newInstance(int num) {
        MyFragment f = new MyFragment();

        // Supply num input as an argument.
        Bundle args = new Bundle();
        args.putInt("num", num);
        f.setArguments(args);

        return f;
    }

    /**
     * When creating, retrieve this instance's number from its arguments.
     */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mNum = getArguments() != null ? getArguments().getInt("num") : 1;
    }

    /**
     * The Fragment's UI is just a simple text view showing its
     * instance number.
     */
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.fragment_pager_list, container, false);
        View tv = v.findViewById(R.id.text);
        if(mNum == 6){
            mNum=1;
        }else if(mNum==7){
            mNum=5;
        }else if(mNum==0){
            mNum=5;
        }
        ((TextView)tv).setText("Fragment #" + mNum);
        return v;
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        setListAdapter(new ArrayAdapter<String>(getActivity(),
                android.R.layout.simple_list_item_1, new String[] {"test1","test2","test3","test4","Test5"}));
    }

    @Override
    public void onListItemClick(ListView l, View v, int position, long id) {
        Log.i("FragmentList", "Item clicked: " + id);
    }
}

}

1

这是一个相当巧妙的方法,但对我来说效果非常好:

@Override
public int getCount() {
    return NUM_ITEMS * 1000;
}

这将使您的页面“循环”1000次。 不要忘记在getItem上使用%操作,就像这样

@Override
public Fragment getItem(int position) {
    position = position % 1000;
    return MyFragment.newInstance(position);
}

1
实际上,我找到了一种更好、更优雅的方法。在这种情况下,我有“n”个屏幕(3个),由于我想在列表末尾返回到第一个屏幕,所以我“添加另一个屏幕”,它只是最后一个屏幕的精确副本,并且对于反向也是如此。基本上,现在我有“n”个屏幕+2(或者在这种情况下是5)。屏幕设置如下:C的副本,ABCA的副本然后我设置手势监听器并跟踪我所在的页面,如果在列表末尾,我将移动到第一页,即最后一页的副本,模拟循环。 - tyczj
以答案形式发布,这种方法更好,因此其他人也可以受益。 - Entreco

0

我基于tyczj的答案编写了一个Kotlin解决方案,它可以处理当轮播项在适配器创建后加载(例如从服务器加载项)并且不会获取触摸监听器,而是等待ViewPager2的空闲状态。在我的情况下,我有一个用户资料的轮播。

根据tycjz的答案,如果我们有一组项目A B C D,那么ViewPager2的功能最终变成C A B C D A,但我们从位置1开始ViewPager2,而不是0,所以它最终停留在A

inner class UserProfileSlidePagerAdapter(fa: FragmentActivity) : FragmentStateAdapter(fa) {

    var profileToJumpTo: Int? = null

    override fun getItemCount(): Int {
        if (userIdsForLocalUsers.size > 0) {
            return userIdsForLocalUsers.size + 2
        }
        return userIdsForLocalUsers.size
    }

    override fun createFragment(position: Int): Fragment {
        var positionToUse = position - 1
        if (position > userIdsForLocalUsers.size)
        {
            positionToUse = 0
        }
        if (positionToUse < 0)
        {
            positionToUse = userIdsForLocalUsers.size - 1
        }
        val userId = userIdsForLocalUsers[positionToUse]
        this@ProfileViewModel.availableUserProfilesHash[userId].let {userProfile ->
            return CarouselUserProfileFragment.newInstance(userProfile!!)
        }
    }
}

在解决了PageAdapter的“off by 1”定位问题之后,你可以通过ViewPager2的onPageSelected事件判断循环是否到达了开始或结束,并且在onPageScrollStateChanged处选择要跳转到哪一页。因此,在包含ViewPager2的Fragment中:

this.profiles_view_pager.registerOnPageChangeCallback(object: ViewPager2.OnPageChangeCallback() {
    override fun onPageScrollStateChanged(state: Int) {
        if (state == ViewPager2.SCROLL_STATE_IDLE) {
            val adapter = this@CarouselFragment.profiles_view_pager.adapter as ProfileViewModel.UserProfileSlidePagerAdapter
            val profileToJumpTo = adapter.profileToJumpTo
            profileToJumpTo?.let {
                this@CarouselFragment.profiles_view_pager.setCurrentItem(profileToJumpTo, false)
                adapter.profileToJumpTo = null
            }
        }
        super.onPageScrollStateChanged(state)
    }
    override fun onPageSelected(position: Int) {
        val adapter = this@CarouselFragment.profiles_view_pager.adapter as ProfileViewModel.UserProfileSlidePagerAdapter
        adapter.itemCount.let { itemCount ->
            if (position == 0) {
                adapter.profileToJumpTo = itemCount - 2
            }
            if (position == itemCount - 1) {
                adapter.profileToJumpTo = 1
            }
        }
        super.onPageSelected(position)
    }
})

我还有LiveData来观察并将当前项设置为“+1”。

this.profileViewModel.loadUserProfilesResult.observe(viewLifecycleOwner, Observer {     
    this.profiles_view_pager.setCurrentItem(1, false)
 })

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