ViewPager中的片段无法正常工作

Question

我在viewpager中有3个选项卡，在所有3个片段中，我都使用改造功能来调用服务器，但是当我启动活动时，首先调用了2个片段，并且从两个网络中都调用了该功能，当我定位到下一个选项卡时，没有任何显示，并且位置变为2。

问题是，当我进入活动视图时，寻呼机已初始化，并且寻呼机适配器返回两个位于位置0和1的片段，并对两个片段都进行充气处理，因此从这两个位置都调用了网络，但是当我将Tab键移至下一个位置时，它变为2。 。应该为1。

适配器类别：

public class PagerAdapter extends FragmentStatePagerAdapter {

private int mNumTabs;

    public PagerAdapter(FragmentManager fm, int numTabs) {
        super(fm);
        this.mNumTabs= numTabs;
    }

    @Override
    public Fragment getItem(int position) {
        switch (position) {

            case 0:
                Fragment1 tab0 = new Fragment1();
                return tab0;
            case 1:
                Fragment2 tab1 = new Fragment2();
                return tab1;
            case 2:
                Fragment3 tab2 = new Fragment3();
                return tab2;
            default:
                return null;
        }
    }

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

}

活动类别：

public class UserProfileScreen extends AppCompatActivity {

    private ViewPager viewPager;
    private TabLayout tabLayout;
    private Context context;      
    private PagerAdapter PagerAdapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_user_profile_screen);
        context = this;
        initViews();
    tabLayout.addTab(tabLayout.newTab().setText("About"));
        tabLayout.addTab(tabLayout.newTab().setText("Session"));
        tabLayout.addTab(tabLayout.newTab().setText("Subjects"));
        pagerAdapter = new PagerAdapter(getSupportFragmentManager(), tabLayout.getTabCount());
        viewPager.setAdapter(profilePagerAdapter);
        viewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));
        tabLayout.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
            @Override
            public void onTabSelected(TabLayout.Tab tab) {
                viewPager.setCurrentItem(tab.getPosition());
            }
            @Override
            public void onTabUnselected(TabLayout.Tab tab) {
                //Toast.makeText(context, "Unselected",Toast.LENGTH_LONG).show();
            }

            @Override
            public void onTabReselected(TabLayout.Tab tab) {
                //Toast.makeText(context, "Reselected",Toast.LENGTH_LONG).show();
            }
        });
    }

    private void initViews(){
        myToolbar = (Toolbar) findViewById(R.id.toolbar);
        tabLayout = (TabLayout) findViewById(R.id.profile_tab_layout);
        setSupportActionBar(myToolbar);
        viewPager = (ViewPager) findViewById(R.id.profile_viewPager);
    }

}

片段1：

public class Fragment1 extends Fragment {

    private RecyclerView sessions_recycler_view;
    private SessionsAdapter sessionsAdapter;
    private SessionProfileFragmentPresenter presenter;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        sessionsAdapter = new SessionsAdapter(getContext(),this);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_profile,container,false);

        sessions_recycler_view = (RecyclerView) view.findViewById(R.id.sessions_list);
        sessions_recycler_view.setAdapter(sessionsAdapter);

     //Server Call to get List<HashMap<String,Object>> data

      setDataToAdapter(data);

        return view;
    }


    private void setDataToAdapter(List<HashMap<String, Object>> sessions) {
        sessionsAdapter.setData(sessions);
    }

}

Fragment2也与Fragment1相同。

Answer 1

我支持Pramod Garg的回答

viewPager的默认OffscreenPageLimit为1，因此以下代码可能对您有用。 我刚刚添加了viewpager.setOffscreenPageLimit（2）行。

 @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_user_profile_screen);
        context = this;
        initViews();
    tabLayout.addTab(tabLayout.newTab().setText("About"));
        tabLayout.addTab(tabLayout.newTab().setText("Session"));
        tabLayout.addTab(tabLayout.newTab().setText("Subjects"));
        pagerAdapter = new PagerAdapter(getSupportFragmentManager(), tabLayout.getTabCount());
        viewPager.setAdapter(profilePagerAdapter);
        viewpager.setOffscreenPageLimit(2)
        viewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));
        tabLayout.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
            @Override
            public void onTabSelected(TabLayout.Tab tab) {
                viewPager.setCurrentItem(tab.getPosition());
            }
            @Override
            public void onTabUnselected(TabLayout.Tab tab) {
                //Toast.makeText(context, "Unselected",Toast.LENGTH_LONG).show();
            }

            @Override
            public void onTabReselected(TabLayout.Tab tab) {
                //Toast.makeText(context, "Reselected",Toast.LENGTH_LONG).show();
            }
        });
    }