在导航抽屉片段中保存视图页面片段的状态答案

【问题标题】：Save state of viewpager fragment in navigation drawer fragments在导航抽屉片段中保存视图页面片段的状态
【发布时间】：2018-08-01 21:14:56
【问题描述】：

我有导航抽屉。在导航抽屉的第一个片段中，有 viewpager，并且有来自网络的信息。Viewpager 也有 2 个片段。当我将片段切换到导航抽屉的设置片段并返回到这个片段时，一切都是消失了..没有任何信息..我怎样才能保存这个片段的状态？或者我可以通过哪种方法发送请求以再次从网络获取信息

主活动

          public class MainActivity extends AppCompatActivity implements 

        NavigationView.OnNavigationItemSelectedListener {

        private DrawerLayout drawer;

@Override

protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);

    setContentView(R.layout.activity_main);

    drawer = (DrawerLayout) findViewById(R.id.drawer_layout);


    NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
    navigationView.setNavigationItemSelectedListener(this);

    getSupportFragmentManager()
            .beginTransaction()
            .replace(R.id.motherFragments, FragmentMainPage.newInstance("MainPage"))
            .commit();
}

@Override
public void onBackPressed() {
   drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    if (drawer.isDrawerOpen(GravityCompat.START)) {
        drawer.closeDrawer(GravityCompat.START);
    } else {
        super.onBackPressed();
    }
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
        case android.R.id.home: {
            drawer.openDrawer(GravityCompat.START);
            break;
        }

    }

    return super.onOptionsItemSelected(item);
}

@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
    Fragment fragment = null;

    if (item.isChecked()) {
        drawer.closeDrawer(GravityCompat.START);
        return false;
    }
    switch (item.getItemId()) {

        case R.id.home: {
            fragment = new FragmentMainPage().newInstance("Sample");
            break;
        }
        case R.id.settings:{
            Intent intent = new Intent(this,SettingsActivity.class);
            startActivity(intent);
            break;
        }
        case R.id.incoming:{
            fragment  = new FragmentIncomingPage().newInstance("Sample");
            break;
        }

    }

    if (fragment != null) {
        getSupportFragmentManager()
                .beginTransaction().replace(R.id.motherFragments, fragment)
                .commit();
        item.setChecked(true);

    }

    drawer.closeDrawer(GravityCompat.START);
    return true;
} }

导航抽屉的Fragment1

            public class FragmentMainPage extends Fragment implements 
         ViewPager.OnPageChangeListener {
             private Toolbar toolbar;
              private MainActivity activity;
           private TabLayout tabLayout;
             private ViewPager viewPager;

String[] names = {
        "Sample 1",
        "Sample 2"

};



private static FragmentMainPage myInstance;
public static FragmentMainPage newInstance(String testString){
    Bundle bundle = new Bundle();
    bundle.putString("test",testString);
    if(myInstance == null){
        myInstance = new FragmentMainPage();
    }
    myInstance.setArguments(bundle);
    return myInstance;
}

@Override
public void onAttach(Context context) {
    super.onAttach(context);
    activity = ((MainActivity) context);
}

@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setHasOptionsMenu(true);
}

@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.activity_fragment_main,container,false);
    toolbar = (Toolbar) view.findViewById(R.id.toolbar);

    activity.setSupportActionBar(toolbar);
    activity.setTitle(getResources().getText(R.string.bosh_sahifa));
    activity.getSupportActionBar().setHomeAsUpIndicator(R.drawable.ic_menu_white_24dp);
    activity.getSupportActionBar().setDisplayHomeAsUpEnabled(true);
    viewPager = (ViewPager) view.findViewById(R.id.viewpager);
    setupViewpager(viewPager);
    tabLayout = (TabLayout) view.findViewById(R.id.tabs);
    tabLayout.setupWithViewPager(viewPager);
    viewPager.addOnPageChangeListener(this);
    setupTabName();

    return view;
}


private void setupViewpager(ViewPager viewPager) {
    MyAdapter adapter = new MyAdapter(getActivity().getSupportFragmentManager());
    adapter.addFragement(new Fragment_home1());
    adapter.addFragement(new Fragment_home2());

    viewPager.setAdapter(adapter);

}

private void setupTabName() {
    tabLayout.getTabAt(0).setText(names[0]);
    tabLayout.getTabAt(1).setText(names[1]);

}

@Override
public void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);


}

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

}

@Override
public void onPageSelected(int position) {

}

@Override
public void onPageScrollStateChanged(int state) {

}

private class MyAdapter extends FragmentPagerAdapter {
    private final List<Fragment> mFragmentList = new ArrayList<>();

    public MyAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public Fragment getItem(int position) {
        return mFragmentList.get(position);
    }

    @Override
    public int getCount() {
        return mFragmentList.size();
    }
    public void addFragement(Fragment fragment){
        mFragmentList.add(fragment);
    }
}

}

导航抽屉的片段 2

             public class FragmentIncomingPage extends Fragment  {
             private Toolbar toolbar;
               private MainActivity activity;




private static FragmentIncomingPage myInstance;
public static FragmentIncomingPage newInstance(String testString){
    Bundle bundle = new Bundle();
    bundle.putString("test",testString);
    if(myInstance == null){
        myInstance = new FragmentIncomingPage();
    }
    myInstance.setArguments(bundle);
    return myInstance;
}

@Override
public void onAttach(Context context) {
    super.onAttach(context);
    activity = ((MainActivity) context);
}

@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setHasOptionsMenu(true);
}

@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.activity_fragment_incoming,container,false);
    toolbar = (Toolbar) view.findViewById(R.id.toolbar);

    activity.setSupportActionBar(toolbar);
    activity.setTitle(getResources().getText(R.string.Incoming));
    activity.getSupportActionBar().setHomeAsUpIndicator(R.drawable.ic_menu_white_24dp);
    activity.getSupportActionBar().setDisplayHomeAsUpEnabled(true);

    return view;
}

}

【问题讨论】：

标签： android navigation fragment drawer

【解决方案1】：

有 3 个片段，然后滑动到第 3 个片段然后回到第 1 个片段，第 1 个片段的数据消失了吗？

【讨论】：

如果你的情况是我上面提到的，请尝试ViewPager.setOffscreenPageLimit(2)
在 viewpager 中没有，我可以使用更多片段。它工作正常...当我更改 viewpager 的母片段并回到这个母片段时，一切都消失了..
你能发布一些关于“当我改变 viewpager 的母片段”的代码片段和“回来”的代码片段
所以你打开Fragment1再打开Fragment2，最后再打开Fragment1，fragment1的数据就没了？
是的，确实是这样..viewpager 片段的数据已经消失

【解决方案2】：

您可以使用 fragment.addToBackStack(null) 方法。喜欢，

FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.replace(R.id.content_frame, A);
ft.addToBackStack(null);
ft.commit();

【讨论】：

我在哪里使用它？在抽屉片段中或在 MainActivity 中切换抽屉片段。？
@JavohirRuzimurodov 当您替换或添加片段时，请使用上述代码。
我照你说的做了..但它仍然丢失数据

【解决方案3】：

实现它的方法很少。

您可以使用 SharedPreferences 通过 mViewPager.getCurrentItem() 保存当前 Fragment，并在您通过导航抽屉按钮进入 ViewPager 活动时再次设置它。
使用 BaseFragment 并从 Base Fragment 实现您的 Fragment，将 View Pager 的当前可见 Fragment 保留在 Base Fragment 中作为受保护的变量。
作为上面描述的Base Fragment，你可以使用Bas Activity类。

【讨论】：