问题
I am using Navigation Drawer to navigate between fragments they all use the MainActivity toolbar but each fragment has it's own TabLayout with 3 tabs and in each tab I am using RecyclerView to show different text and images.
I did this last time using actvities instead of fragments but now using the drawer it's beter to use fragments.
I have got to a point where the tabs work but as soon as I put the ViewPager in and connect the adapters to the tabs and I open the new fragment from the drawer I get a Null Pointer what could be the problem here?
MainActivity.java
public class MainActivity extends AppCompatActivity
implements NavigationView.OnNavigationItemSelectedListener {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
drawer.setDrawerListener(toggle);
toggle.syncState();
NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
navigationView.setNavigationItemSelectedListener(this);
}
@Override
public void onBackPressed() {
DrawerLayout 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) {
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
return id == R.id.action_settings || super.onOptionsItemSelected(item);
}
@Override
public boolean onNavigationItemSelected(MenuItem item) {
int id = item.getItemId();
Fragment fragment;
if (id == R.id.fragment_one) {
fragment = new NewFragment();
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.replace(R.id.container, fragment);
ft.commit();
} else if (id == R.id.fragment_two) {
fragment = new NewFragment();
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.replace(R.id.container, fragment);
ft.commit();
} else if (id == R.id.fragment_three) {
fragment = new NewFragment();
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.replace(R.id.container, fragment);
ft.commit();
}
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
drawer.closeDrawer(GravityCompat.START);
return true;
}
}
activity_main.xml
<android.support.v4.widget.DrawerLayout 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"
android:id="@+id/drawer_layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:openDrawer="start">
<android.support.design.widget.CoordinatorLayout 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"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:context="com.xcandy.guideforfifa17.MainActivity">
<android.support.design.widget.AppBarLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:theme="@style/AppTheme.AppBarOverlay">
<android.support.v7.widget.Toolbar
android:id="@+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="?attr/colorPrimary"
app:popupTheme="@style/AppTheme.PopupOverlay" />
</android.support.design.widget.AppBarLayout>
<include layout="@layout/content_main" />
</android.support.design.widget.CoordinatorLayout>
<android.support.design.widget.NavigationView
android:id="@+id/nav_view"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:layout_gravity="start"
android:fitsSystemWindows="true"
app:headerLayout="@layout/nav_header_main"
app:menu="@menu/activity_main_drawer" />
</android.support.v4.widget.DrawerLayout>
NewFragment.java
public class NewFragment extends Fragment {
private RecyclerView mRecyclerView;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.activity_fragment_one, container, false);
TabLayout tabLayout = (TabLayout) view.findViewById(R.id.tabs);
tabLayout.addTab(tabLayout.newTab().setText("A"));
tabLayout.addTab(tabLayout.newTab().setText("B"));
tabLayout.addTab(tabLayout.newTab().setText("C"));
final ViewPager viewPager = (ViewPager) view.findViewById(R.id.viewpager);
mRecyclerView = (RecyclerView) view.findViewById(R.id.recycler_view);
RecyclerView.LayoutManager mLayoutManager = new LinearLayoutManager(getActivity());
mRecyclerView.setLayoutManager(mLayoutManager);
viewPager.setAdapter(new PagerAdapter
(getFragmentManager(), tabLayout.getTabCount()));
viewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));
tabLayout.setOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
@Override
public void onTabSelected(TabLayout.Tab tab) {
viewPager.setCurrentItem(tab.getPosition());
}
@Override
public void onTabUnselected(TabLayout.Tab tab) {
}
@Override
public void onTabReselected(TabLayout.Tab tab) {
}
});
return view;
}
public class PagerAdapter extends FragmentStatePagerAdapter {
int mNumOfTabs;
public PagerAdapter(FragmentManager fm, int NumOfTabs) {
super(fm);
this.mNumOfTabs = NumOfTabs;
}
@Override
public Fragment getItem(int position) {
switch (position) {
case 0:
RecyclerView.Adapter mAdapter = new AdapterOne();
mRecyclerView.setAdapter(mAdapter);
case 1:
mAdapter = new AdapterTwo();
mRecyclerView.setAdapter(mAdapter);
case 2:
mAdapter = new AdapterThree();
mRecyclerView.setAdapter(mAdapter);
default:
return null;
}
}
@Override
public int getCount() {
return mNumOfTabs;
}
}
}
activity_fragment.xml
<android.support.design.widget.CoordinatorLayout 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"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:context=".NewFragment">
<android.support.design.widget.AppBarLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:theme="@style/AppTheme.AppBarOverlay">
<android.support.design.widget.TabLayout
android:id="@+id/tabs"
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:tabMode="fixed"
app:tabGravity="fill"/>
</android.support.design.widget.AppBarLayout>
<android.support.v4.view.ViewPager
android:id="@+id/viewpager"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="@android:color/white"/>
<android.support.v7.widget.RecyclerView
android:id="@+id/recycler_view"
android:layout_width="match_parent"
android:layout_height="match_parent"
/>
</android.support.design.widget.CoordinatorLayout>
Error Log
--------- beginning of crash
06-23 11:19:56.985 2466-2466/com.candyx.sims E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.candyx.sims, PID: 2466
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setLayoutManager(android.support.v7.widget.RecyclerView$LayoutManager)' on a null object reference
at com.candyx.sims.BlankFragment.onCreateView(BlankFragment.java:38)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:1974)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1252)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:742)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1617)
at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:517)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5254)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
06-23 11:23:14.912 5839-5873/com.candyx.sims D/OpenGLRenderer: Use EGL_SWAP_BEHAVIOR_PRESERVED: true
[ 06-23 11:23:14.920 5839: 5839 D/ ]
HostConnection::get() New Host Connection established 0xb4125190, tid 5839
06-23 11:23:14.927 5839-5839/com.candyx.sims D/Atlas: Validating map...
06-23 11:23:15.011 5839-5873/com.candyx.sims I/OpenGLRenderer: Initialized EGL, version 1.4
06-23 11:23:15.027 5839-5873/com.candyx.sims D/OpenGLRenderer: Enabling debug mode 0
06-23 11:23:15.039 5839-5873/com.candyx.sims W/EGL_emulation: eglSurfaceAttrib not implemented
06-23 11:23:15.039 5839-5873/com.candyx.sims W/OpenGLRenderer: Failed to set EGL_SWAP_BEHAVIOR on surface 0xae838600, error=EGL_SUCCESS
06-23 11:23:16.444 5839-5839/com.candyx.sims W/PathParser: Points are too far apart 4.000000596046461
06-23 11:23:17.342 5839-5839/com.candyx.sims W/PathParser: Points are too far apart 4.000000596046461
06-23 11:23:17.350 5839-5839/com.candyx.sims I/AppCompatViewInflater: app:theme is now deprecated. Please move to using android:theme instead.
06-23 11:23:17.369 5839-5839/com.candyx.sims D/AndroidRuntime: Shutting down VM
06-23 11:23:17.369 5839-5839/com.candyx.sims E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.candyx.sims, PID: 5839
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setLayoutManager(android.support.v7.widget.RecyclerView$LayoutManager)' on a null object reference
at com.candyx.sims.NewFragment.onCreateView(NewFragment.java:38)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:1974)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1252)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:742)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1617)
at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:517)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5254)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
06-23 11:25:16.961 7518-7518/com.candyx.sims W/art: Before Android 4.1, method android.graphics.PorterDuffColorFilter android.support.graphics.drawable.VectorDrawableCompat.updateTintFilter(android.graphics.PorterDuffColorFilter, android.content.res.ColorStateList, android.graphics.PorterDuff$Mode) would have incorrectly overridden the package-private method in android.graphics.drawable.Drawable
06-23 11:25:17.078 7518-7548/com.candyx.sims D/OpenGLRenderer: Use EGL_SWAP_BEHAVIOR_PRESERVED: true
[ 06-23 11:25:17.081 7518: 7518 D/ ]
HostConnection::get() New Host Connection established 0xb412a1f0, tid 7518
06-23 11:25:17.082 7518-7518/com.candyx.sims D/Atlas: Validating map...
06-23 11:25:17.109 7518-7548/com.candyx.sims I/OpenGLRenderer: Initialized EGL, version 1.4
06-23 11:25:17.126 7518-7548/com.candyx.sims D/OpenGLRenderer: Enabling debug mode 0
06-23 11:25:17.134 7518-7548/com.candyx.sims W/EGL_emulation: eglSurfaceAttrib not implemented
06-23 11:25:17.134 7518-7548/com.candyx.sims W/OpenGLRenderer: Failed to set EGL_SWAP_BEHAVIOR on surface 0xb41234c0, error=EGL_SUCCESS
06-23 11:25:31.030 7518-7518/com.candyx.sims W/PathParser: Points are too far apart 4.000000596046461
06-23 11:25:32.174 7518-7518/com.candyx.sims W/PathParser: Points are too far apart 4.000000596046461
06-23 11:25:32.187 7518-7518/com.candyx.sims I/AppCompatViewInflater: app:theme is now deprecated. Please move to using android:theme instead.
06-23 11:25:32.207 7518-7518/com.candyx.sims D/AndroidRuntime: Shutting down VM
06-23 11:25:32.207 7518-7518/com.candyx.sims E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.candyx.sims, PID: 7518
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setLayoutManager(android.support.v7.widget.RecyclerView$LayoutManager)' on a null object reference
at com.candyx.sims.NewFragment.onCreateView(NewFragment.java:38)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:1974)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1252)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:742)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1617)
at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:517)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5254)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
回答1:
After looking into yours code, I found that you forget to return a fragment in getItem method of PagerAdapter that you overrided from the FragmentStatePagerAdapter and there is no break statement in each case due to which every time a null value was returned.
To doing so you need to create a another new fragment for each page in ViewPager or you can create one new fragment that could use in all page of ViewPager.
You can't use the same recyclerview into the tabs of view pager that you have defined in parent fragment.
activity_fragment_one.xml
<android.support.design.widget.CoordinatorLayout 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"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:context=".NewFragment">
<android.support.design.widget.AppBarLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:theme="@style/AppTheme.AppBarOverlay">
<android.support.design.widget.TabLayout
android:id="@+id/tabs"
android:layout_width="match_parent"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
app:tabTextAppearance="?android:attr/textAppearanceMedium"
app:tabTextColor="#ffffff"
android:layout_height="?android:actionBarSize"
app:tabMode="fixed"
app:tabGravity="fill"/>
</android.support.design.widget.AppBarLayout>
<android.support.v4.view.ViewPager
android:id="@+id/viewpager"
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
android:background="@android:color/white"/>
</android.support.design.widget.CoordinatorLayout>
I have fixed your fragment and created a new Fragment that you can use in ViewPager Pages.
public class NewFragment extends Fragment {
private RecyclerView mRecyclerView;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.activity_fragment_one, container, false);
TabLayout tabLayout = (TabLayout) view.findViewById(R.id.tabs);
tabLayout.addTab(tabLayout.newTab().setText("A"));
tabLayout.addTab(tabLayout.newTab().setText("B"));
tabLayout.addTab(tabLayout.newTab().setText("C"));
final ViewPager viewPager = (ViewPager) view.findViewById(R.id.viewpager);
// mRecyclerView = (RecyclerView) view.findViewById(R.id.recycler_view);
LinearLayoutManager mLayoutManager = new LinearLayoutManager(getActivity());
mLayoutManager.setOrientation(LinearLayoutManager.VERTICAL);
//mRecyclerView.setLayoutManager(mLayoutManager);
viewPager.setAdapter(new PagerAdapter(getFragmentManager(), tabLayout.getTabCount()));
viewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));
tabLayout.setupWithViewPager(viewPager);
tabLayout.setTabMode(TabLayout.MODE_SCROLLABLE);
tabLayout.setOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
@Override
public void onTabSelected(TabLayout.Tab tab) {
viewPager.setCurrentItem(tab.getPosition());
}
@Override
public void onTabUnselected(TabLayout.Tab tab) {
}
@Override
public void onTabReselected(TabLayout.Tab tab) {
}
});
return view;
}
public class PagerAdapter extends FragmentStatePagerAdapter {
int mNumOfTabs;
public PagerAdapter(FragmentManager fm, int NumOfTabs) {
super(fm);
this.mNumOfTabs = NumOfTabs;
}
@Override
public Fragment getItem(int position) {
switch (position) {
case 0:
return new FragmentTab();
case 1:
return new FragmentTab();
case 2:
return new FragmentTab();
default:
return null;
}
}
@Override
public int getCount() {
return mNumOfTabs;
}
}
}
FragmentTab for each Page in View Pager (or you can create different fragment for each page according to yours need).
public class FragmentTab extends Fragment {
RecyclerView mRecyclerView;
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_tab, container, false);
mRecyclerView = (RecyclerView) view.findViewById(R.id.recycler_view);
LinearLayoutManager mLayoutManager = new LinearLayoutManager(getActivity());
mLayoutManager.setOrientation(LinearLayoutManager.VERTICAL);
mRecyclerView.setLayoutManager(mLayoutManager);
RecyclerView.Adapter mAdapter = new AdapterOne();
mRecyclerView.setAdapter(mAdapter);
return view;
}
}
fragment_tab.xml
<?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">
<android.support.v7.widget.RecyclerView
android:id="@+id/recycler_view"
android:layout_width="match_parent"
android:layout_height="match_parent"
/>
</LinearLayout>
回答2:
Use getChildFragmentManager() instead of getSupportFragmentManager()
回答3:
Without the error logs, it's difficult to say where and why do you get the NullPointerException.
The first thing that caught my attention is that you didn't link your TabLayout and ViewPager. Use the following code after you set the adapter for the ViewPager:
// setUpWithViewPager doesn't work without using a Runnable interface.
// Support library bug, maybe?
tabLayout.post(new Runnable() {
@Override
public void run() {
tabLayout.setupWithViewPager(viewPager);
}
});
I'm not sure if this is the problem, but give it a try :)
回答4:
Well, some time ago I implemented exactly the same app design. I had a fragment, that intended to hold Tabs and ViewPager. That was a tricky task, and I recall that I faced similar problems as you did. Here is how I solved it:
The layout sequence is:
Activity -> Fragment -> Tab Layout + ViewPager -> FragmentStatePagerAdapter -> Fragment -> RecyclerView
You've got nothing to do with your Main Activity. All the stuff is in fragments. So get rid from TabLayout in your activity_main.xml.
You will have to deal with nested fragments inside pager. All page content must be there and TabLayout must be in the same layout where you ViewPager is.
My project is a bit old, and I used android.support.v4.app.Fragment in case if it makes sense. I stripped sources from data you wont need, so you may see refers to some orphaned methods.
The task was to display price list with categories, and render each category products on its own page, so that horizontal swipes would switch categories and vertical swipes — list products.
Each fragment with ViewPager and TabLayout has following subfragment_price_list_pager.xml layout:
<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.CardView 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"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@color/icons"
app:cardCornerRadius="4dp"
app:cardElevation="4dp"
app:cardPreventCornerOverlap="true">
<android.support.v7.widget.Toolbar
android:id="@+id/priceListToolbar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:elevation="4dp"
android:theme="@style/AppTheme.Toolbar.TabLayout"
app:navigationIcon="@drawable/ic_tag_multiple_grey600_24dp"
tools:ignore="UnusedAttribute">
<android.support.design.widget.TabLayout
android:id="@+id/tabBar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true" />
</android.support.v7.widget.Toolbar>
<android.support.v4.view.ViewPager
android:id="@+id/priceList"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginTop="58dp"
android:padding="5dp"
android:scrollbars="horizontal" />
</android.support.v7.widget.CardView>
Here is the PriceListPagerFragment.class:
public class PriceListPagerFragment extends Fragment {
private static final String TAG = "PriceListPagerFragment";
private PriceList mPriceList;
private ViewPager mCategoriesViewPager;
private TabLayout tabLayout;
private Loader<PriceList> priceListLoader;
private EditText scanerBarcodeText;
private OnCartActionListener mListener;
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.subfragment_price_list_pager, container, false);
// Pager that would be inflated with page fragments.
mCategoriesViewPager = (ViewPager) rootView.findViewById(R.id.priceList);
tabLayout = (TabLayout) rootView.findViewById(R.id.tabBar);
tabLayout.setTabMode(TabLayout.MODE_SCROLLABLE);
// Do all the stuff with pager here:
updatePriceListPages();
return rootView;
}
private void updatePriceListPages() {
if (mCategoriesViewPager != null && mPriceList != null) {
Log.d(TAG, this + "updatePriceListPages");
if (mCategoriesViewPager.getAdapter() == null) {
PriceListCategoriesAdapter adapter = new PriceListCategoriesAdapter(
getFragmentManager(),
tabLayout
);
mCategoriesViewPager.setAdapter(
adapter
);
// Each page is a content of a single category of one-level catalog
// We did not supply catalog to adapter before it is bound to ViewPager for some serious reason which I can't recall now
adapter.setPriceList(mPriceList);
tabLayout.setupWithViewPager(mCategoriesViewPager);
} else {
((PriceListCategoriesAdapter) mCategoriesViewPager.getAdapter()).setPriceList(mPriceList);
}
}
}
}
Custom FragmentStatePagerAdapter implementation, PriceListCategoriesAdapter.class:
public class PriceListCategoriesAdapter extends FragmentStatePagerAdapter {
private static final String TAG = "PriceListCategoriesAd";
private final TabLayout mTabLayout;
private FragmentManager mFm;
private Vector<PriceListFragment> recyclerViewList;
private Vector<String> titles;
public PriceListCategoriesAdapter(FragmentManager fm, TabLayout tabLayout) {
super(fm);
mFm = fm;
mTabLayout = tabLayout;
recyclerViewList = new Vector<>();
titles = new Vector<>();
}
// All the magic with nested page fragments is done here
public void setPriceList(PriceList priceList) {
boolean updateTabs = false;
Vector<String> newTitles = new Vector<>();
int position = 0;
for (CatalogItem catalogItem : priceList.getCatalogs()) {
if (catalogItem.getProducts() == null)
continue;
boolean newFragment;
PriceListFragment fragment;
try {
fragment = recyclerViewList.get(position);
newFragment = false;
} catch (ArrayIndexOutOfBoundsException e) {
fragment = new PriceListFragment();
newFragment = true;
}
fragment.setCatalogItem(catalogItem);
newTitles.add(catalogItem.getName());
if (newFragment) {
recyclerViewList.add(fragment);
}
position++;
}
if (titles.size() != newTitles.size()) {
updateTabs = true;
} else {
for (int position = 0; position < titles.size(); position++) {
if (!titles.get(position).equals(newTitles.get(position))) {
updateTabs = true;
break;
}
}
}
titles = newTitles;
notifyDataSetChanged();
if (updateTabs)
mTabLayout.setTabsFromPagerAdapter(this);
}
@Override
public Fragment getItem(int position) {
return recyclerViewList.get(position);
}
@Override
public int getItemPosition(Object object) {
PriceListFragment fragment = (PriceListFragment) object;
String title = (String) fragment.getTitle();
int position = titles.indexOf(title);
if (position >= 0) {
return position;
} else {
return POSITION_NONE;
}
}
@Override
public int getCount() {
return titles.size();
}
@Override
public CharSequence getPageTitle(int position) {
return recyclerViewList.get(position).getTitle();
}
// We don't keep states
@Override
public Parcelable saveState() {
return null;
}
// We don't keep states
@Override
public void restoreState(Parcelable state, ClassLoader loader) {
}
}
And finally PriceListFragment layout:
<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.RecyclerView android:id="@+id/categoryList"
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:scrollbars="vertical" />
PriceListFragment.class itself has nothing special. Just instantiate it's RecyclerView with proper data.
回答5:
i suggest using getChildFragmentManager instead of getFragmentManager in
viewPager.setAdapter(new PagerAdapter
(getFragmentManager(), tabLayout.getTabCount()));
回答6:
This method getItem in PagerAdapter wrong, it return Fragment init
You should return Fragment. And in fragment, you setView recyclerView to it
来源：https://stackoverflow.com/questions/35058819/android-tablayout-inside-fragment