【发布时间】：2019-09-23 13:04:17
【问题描述】：
我正在开发一个 android 应用程序，它有一个底部导航，可以在没有 viewpager 的情况下打开 3 个不同的片段。一个片段内部有一个查看器，可打开 2 个片段。这两个片段是同一个片段，每个片段里面都有一个 recyclerview。我的问题是，当我运行应用程序时，除了 viewpager 之外的所有内容都按预期运行。我尝试将片段放入 viewpager 而不是它，并且片段可以工作。我什至尝试将 viewpager 放在一个空的活动中，它也很有效。
这是我的 MainActivity，它包含 BottomNavigation 及其功能：
public class MainActivity extends AppCompatActivity implements BottomNavigationView.OnNavigationItemSelectedListener {
private androidx.appcompat.widget.Toolbar toolbar;
private BottomNavigationView navView;
private Fragment fragment1 = new HomeFragment();
private Fragment fragment2 = new SearchFragment();
private Fragment fragment3 = new SettingsFragment();
private FragmentManager fm = getSupportFragmentManager();
private Fragment active = fragment1;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
toolbar = findViewById(R.id.action_bar);
setSupportActionBar(toolbar);
getSupportActionBar().setTitle("Home");
fm.beginTransaction().add(R.id.main_container, fragment3, "settings").hide(fragment3).commit();
fm.beginTransaction().add(R.id.main_container, fragment2, "search").hide(fragment2).commit();
fm.beginTransaction().add(R.id.main_container, fragment1, "home").commit();
navView = findViewById(R.id.nav_view);
navView.setOnNavigationItemSelectedListener(this);
}
@Override
public boolean onNavigationItemSelected(@NonNull MenuItem menuItem) {
switch (menuItem.getItemId()) {
case R.id.navigation_home:
fm.beginTransaction().hide(active).show(fragment1).addToBackStack("home").commit();
active = fragment1;
toolbar.setTitle("Home");
return true;
case R.id.navigation_search:
fm.beginTransaction().hide(active).show(fragment2).addToBackStack("search").commit();
active = fragment2;
toolbar.setTitle("Search");
return true;
case R.id.navigation_settings:
fm.beginTransaction().hide(active)
.show(fragment3).addToBackStack("settings").commit();
active = fragment3;
toolbar.setTitle("Settings");
return true;
}
return false;
}
public void setCurrentPage(Fragment fragment, int position) {
if(fm.findFragmentByTag("playlist"+position) != null){
fm.beginTransaction().remove(fragment).hide(active).add(R.id.main_container, fragment, "playlist"+position).addToBackStack(null).commit();
active = fragment;
} else {
fm.beginTransaction().hide(active).add(R.id.main_container, fragment, "playlist"+position).addToBackStack(null).commit();
active = fragment;
}
}
}
这是 MainActivityLayout：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
tools:context=".MainActivity">
<include
layout="@layout/action_bar"
android:id="@+id/action_bar"/>
<androidx.core.widget.NestedScrollView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginTop="56dp"
android:layout_marginBottom="70dp"
android:id="@+id/main_container_parent">
<FrameLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
android:id="@+id/main_container"/>
</androidx.core.widget.NestedScrollView>
<com.google.android.material.bottomnavigation.BottomNavigationView
android:id="@+id/nav_view"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="?android:attr/windowBackground"
android:layout_alignParentBottom="true"
app:menu="@menu/bottom_nav_menu"
app:itemTextColor="@color/bottom_nav_color"
app:itemIconTint="@color/bottom_nav_color"
android:elevation="20dp"/>
</RelativeLayout>
这是我实现 ViewPager 的 Fragment：
public class HomeFragment extends Fragment {
@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
return inflater.inflate(R.layout.fragment_home, container, false);
}
@Override
public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
PlaylistsPagerAdapter playlistsPagerAdapter = new PlaylistsPagerAdapter(getChildFragmentManager());
playlistsPagerAdapter.addFragment(new PlaylistsFragment(),"private");
playlistsPagerAdapter.addFragment(new PlaylistsFragment(),"public");
ViewPager viewPager = view.findViewById(R.id.pager_home);
viewPager.setAdapter(playlistsPagerAdapter);
TabLayout tabLayout = view.findViewById(R.id.tab_layout_home);
tabLayout.setupWithViewPager(viewPager);
setHasOptionsMenu(false);
}
public class PlaylistsPagerAdapter extends FragmentStatePagerAdapter {
ArrayList<Fragment> mFragmentList = new ArrayList<>();
ArrayList<String> mFragmentListTitle = new ArrayList<>();
public void addFragment(Fragment playlistsFragment, String title) {
mFragmentListTitle.add(title);
mFragmentList.add(playlistsFragment);
}
public PlaylistsPagerAdapter(FragmentManager fm) {
super(fm);
}
@NonNull
@Override
public Fragment getItem(int i) {
return mFragmentList.get(i);
}
@Override
public int getCount() {
return mFragmentList.size();
}
@Override
public CharSequence getPageTitle(int position) {
return mFragmentListTitle.get(position);
}
}
}
这是 HomeFragmentLayout：
<?xml version="1.0" encoding="utf-8"?>
<androidx.viewpager.widget.ViewPager
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/pager_home"
android:layout_width="match_parent"
android:layout_height="match_parent">
<com.google.android.material.tabs.TabLayout
android:id="@+id/tab_layout_home"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
</androidx.viewpager.widget.ViewPager>
这是播放列表片段：
public class PlaylistsFragment extends Fragment {
private static final String TAG = "PlaylistsFragment";
private ArrayList<String> mPlaylistName = new ArrayList<>();
@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
return inflater.inflate(R.layout.fragment_playlists, container, false);
}
@Override
public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
initNameBitmap(view);
}
private void initNameBitmap(View view){
mPlaylistName.add("Playlist1");
mPlaylistName.add("Playlist2");
mPlaylistName.add("Playlist3");
mPlaylistName.add("Playlist4");
initRecyclerView(view);
}
private void initRecyclerView(View view){
RecyclerView recyclerView = view.findViewById(R.id.recycler_view_playlists);
RecyclerViewAdapterPlaylists recyclerViewAdapterPlaylists = new RecyclerViewAdapterPlaylists(mPlaylistName, view.getContext(),this);
recyclerView.setAdapter(recyclerViewAdapterPlaylists);
recyclerView.setLayoutManager(new LinearLayoutManager(getView().getContext()));
}
}
这是 PlaylistsFragments 布局：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">
<androidx.recyclerview.widget.RecyclerView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/recycler_view_playlists"
android:layout_margin="10dp" />
</LinearLayout>
奇怪的是它已经起作用了。我尝试了 onBackPressed ，当我实现这个并在底部导航上按下另一个视图而不是手机上的后退按钮和主页按钮时，它显示为意图：
fm.beginTransaction().hide(active).show(fragmentsHistory.get(fragmentsHistory.size()-1));
active = fragmentsHistory.get(fragmentsHistory.size()-1)
fragmentsHistory.remove(fragmentsHistory.size()-1);
我做错了什么？ 感谢您的帮助！
【问题讨论】：
-
可以上传xml文件吗？
-
好的，我添加了 xml 文件
标签： android android-fragments android-viewpager fragment