当我回到片段时防止重复项目
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【中文标题】当我回到片段时防止重复项目【英文标题】：Prevent repeating of items when i back to fragment 【发布时间】：2021-10-31 08:38:59 【问题描述】：在我的应用程序中，我的 ViewPager 包含 3 个片段（Home、Profile 等）
Home Fragment 包含 RecyclerView
当我从Home Fragment 导航到Profile Fragment 或More Fragment 时，它按预期工作。
但是当我导航回 Home Fragment 时，RecyclerView 中的项目重复...
当我再次导航时，它再次重复
这是我的 MainActivity.java 代码：
public class MainActivity extends AppCompatActivity
TabLayout mainTabLayout;
ViewPager mainViewPager;
@Override
protected void onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mainTabLayout = findViewById(R.id.main_tablayout);
mainViewPager = findViewById(R.id.main_viewpager);
mainTabLayout.setupWithViewPager(mainViewPager);
//to put mainTabLayout Icons...
MainTabLayoutIcons();
//to Change MainLayout Icons...
private void MainTabLayoutIcons()
ViewPagerAdapter adapter = new ViewPagerAdapter(getSupportFragmentManager());
// add fragments to the adapter
adapter.addFragment(new Home());
adapter.addFragment(new MyActivity());
adapter.addFragment(new More());
mainViewPager.setOffscreenPageLimit(0);
mainViewPager.setAdapter(adapter);
// Select Home tab as default tab on startup
mainViewPager.setCurrentItem(0);
mainTabLayout.getTabAt(0).select();
// Set tabs Initial icons
mainTabLayout.getTabAt(0).setIcon(R.drawable.home_black);
mainTabLayout.getTabAt(1).setIcon(R.drawable.user_outline);
mainTabLayout.getTabAt(2).setIcon(R.drawable.more_outline);
/* tabSelectedListener to change the icon color once it is selected
// and change it back once another tab is selected */
mainTabLayout.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener()
@Override
public void onTabSelected(TabLayout.Tab tab)
if (tab.getPosition() == 0)
mainTabLayout.getTabAt(0).setIcon(R.drawable.home_black);
mainTabLayout.getTabAt(1).setIcon(R.drawable.user_outline);
mainTabLayout.getTabAt(2).setIcon(R.drawable.more_outline);
if (tab.getPosition() == 1)
mainTabLayout.getTabAt(0).setIcon(R.drawable.home_outline);
mainTabLayout.getTabAt(1).setIcon(R.drawable.user_);
mainTabLayout.getTabAt(2).setIcon(R.drawable.more_outline);
if (tab.getPosition() == 2)
mainTabLayout.getTabAt(0).setIcon(R.drawable.home_outline);
mainTabLayout.getTabAt(1).setIcon(R.drawable.user_outline);
mainTabLayout.getTabAt(2).setIcon(R.drawable.more_black);
@Override
public void onTabUnselected(TabLayout.Tab tab)
//no need for it
@Override
public void onTabReselected(TabLayout.Tab tab)
//no need for it
);
这里是ViewPagerAdapter代码：
//Adapter for mainActivity ...
public class ViewPagerAdapter extends FragmentStatePagerAdapter
private final List<Fragment> fragmentList = new ArrayList<>();
public ViewPagerAdapter(@NonNull FragmentManager fm)
super(fm);
@Override
public Fragment getItem(int position)
return fragmentList.get(position);
@Override
public int getCount()
return fragmentList.size();
public void addFragment(Fragment fragment)
fragmentList.add(fragment);
这里是第一个片段Home.java代码：
public class Home extends Fragment
View v;
public SwipeRefreshLayout mSwipeRefreshLayout;
public RecyclerView mainRecyclerView;
private LinearLayoutManager linearLayoutManager;
public final List<MyActivityModel> mainPosts = new ArrayList<>();
private PostAdapter mAdapter;
public Home()
/*Required Empty Constructor... */
@Override
public View onCreateView(LayoutInflater layoutInflater, ViewGroup container, Bundle bundle)
v = layoutInflater.inflate(R.layout.fragment_home, container, false);
mSwipeRefreshLayout = (SwipeRefreshLayout) v.findViewById(R.id.mainSwipeRefresh);
mainRecyclerView = (RecyclerView) v.findViewById(R.id.MainRecyclerView);
linearLayoutManager = new LinearLayoutManager(getActivity());
mainRecyclerView.setLayoutFrozen(true);
mainRecyclerView.setNestedScrollingEnabled(false);
mainRecyclerView.setLayoutManager(linearLayoutManager);
mAdapter = new PostAdapter(mainPosts);
mainRecyclerView.setAdapter(mAdapter);
Swipe();
LoadPosts();
return v;
/**
* -----------------TODO: to load posts in Home RecyclerView...----------------
*/
public void LoadPosts()
Query database = FirebaseDatabase.getInstance().getReference().child("Posts");
database.addChildEventListener(new ChildEventListener()
@Override
public void onChildAdded(@NonNull DataSnapshot snapshot, @Nullable String previousChildName)
if (snapshot.exists())
MyActivityModel post = snapshot.getValue(MyActivityModel.class);
mainPosts.add(0, post);
mAdapter.notifyDataSetChanged();
@Override
public void onChildChanged(@NonNull DataSnapshot snapshot, @Nullable String previousChildName)
@Override
public void onChildRemoved(@NonNull DataSnapshot snapshot)
@Override
public void onChildMoved(@NonNull DataSnapshot snapshot, @Nullable String previousChildName)
@Override
public void onCancelled(@NonNull DatabaseError error)
);
private void Swipe()
//to refresh page after swipe
mSwipeRefreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener()
@Override
public void onRefresh()
Handler handler = new Handler();
handler.postDelayed(new Runnable()
@Override
public void run()
try
mainPosts.clear();
LoadPosts();
mSwipeRefreshLayout.setRefreshing(false);
Toast.makeText(v.getContext(),"Refreshed", Toast.LENGTH_SHORT).show();
catch (Exception e)
mSwipeRefreshLayout.setRefreshing(false);
, 500);
);
这是an image showing item reeating
任何人都可以帮助我如何防止这种重复...
【问题讨论】：
【参考方案1】：您可能需要使用 FragmentPagerAdapter 而不是 FragmentStatePagerAdapter。另外，将mainRecyclerView.setLayoutFrozen(true); 设置为 false，因为它会停止 recyclerView 中的所有内容。
何时需要使用 FragmentPagerAdapter？
FragmentStatePagerAdapter 在数量较多时更有用 页面，更像是一个列表视图。当页面不可见时 用户，他们的整个片段可能会被销毁，只保留 该片段的保存状态。 这允许寻呼机保持 与每个访问的页面相关联的内存要少得多 FragmentPagerAdapter 以潜在的更多开销为代价 在页面之间切换。
FragmentPagerAdapter 示例：
class viewpager_class extends FragmentPagerAdapter
int tabcount;
public viewpager_class(@NonNull FragmentManager fm, int tab_count)
super(fm, tab_count);
this.tabcount = tab_count;
@NonNull
@Override
public Fragment getItem(int position)
switch (position)
case 0:
Fragment1 fragment1 = new Fragment1 ();
return todayBAFragment;
case 1:
Fragment2 fragment2 = new Fragment2 ();
return todayReminderDue;
case 2:
Fragment3 fragment3 = new Fragment3 ();
return currentTransaction;
default:
return null;
@Override
public int getCount()
return tabcount;
另外，将适配器设置到 ViewPager 中，无论您想要显示 viewPager：
//set adapter into viewpager
viewpager_class viewpagerClass = new viewpager_class(getChildFragmentManager(), tabLayout.getTabCount());
viewPager.setAdapter(viewpagerClass);
viewPager.setOffscreenPageLimit(2);
viewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));
【讨论】：
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