Я новичок в Fragments, поэтому извините за вопрос любителя. Мой сценарий в всплеск Activity. Я подключаюсь к API, получаю некоторую информацию и сохраняю их в моем локальном файле (sqlite db), это нормально работает, после этого у меня есть нижняя навигация с 5 кнопками и фрагментами, которые тоже работают нормально, но в категории Fragment язагружаю свою базу данных в Tablayout, где я читаю количество вкладок и имен вкладок из базы данных и снова хочу заполнить вкладки своей базой данных. Здесь я сталкиваюсь с проблемой, когда я получаю некоторые ошибки, но теперь я получаю
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.viewpager.widget.ViewPager.setAdapter(androidx.viewpager.widget.PagerAdapter)' on a null object reference
Я уже много искал о Tablayouts и Fragments, но мне ничего не помогло. если вы думаете, что мой полный проект поможет вам лучше помочь мне, или если я пропустил что-то, чтобы показать, вы можете получить к нему доступ через мой git: https://github.com/pouya16/fansyapp
Вот мой HomeActivity, который делает фрагменты для BottomNavigation:
public class HomeActivity extends AppCompatActivity {
final Fragment homeFragment =new HomeFragment();
final Fragment categoriesFragment = new CategoriesFragment();
final Fragment ordersFragment = new OrdersFragment();
final Fragment profileFragment = new ProfileFragement();
final Fragment backupFragment = new BackupFragement();
final FragmentManager fm = getSupportFragmentManager();
Fragment activeFragment = homeFragment;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_home);
BottomNavigationView navigation = (BottomNavigationView) findViewById(R.id.navigation_bottom_home);
navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener);
fm.beginTransaction().add(R.id.main_container,backupFragment,"5").hide(backupFragment).commit();
fm.beginTransaction().add(R.id.main_container,profileFragment,"4").hide(profileFragment).commit();
fm.beginTransaction().add(R.id.main_container,ordersFragment,"3").hide(ordersFragment).commit();
fm.beginTransaction().add(R.id.main_container,categoriesFragment,"2").hide(categoriesFragment).commit();
fm.beginTransaction().add(R.id.main_container,homeFragment,"1").commit();
}
private BottomNavigationView.OnNavigationItemSelectedListener mOnNavigationItemSelectedListener
=new BottomNavigationView.OnNavigationItemSelectedListener() {
@Override
public boolean onNavigationItemSelected(@NonNull MenuItem item) {
switch (item.getItemId()){
case R.id.navigation_home:
fm.beginTransaction().hide(activeFragment).show(homeFragment).commit();
activeFragment = homeFragment;
return true;
case R.id.navigation_categories:
fm.beginTransaction().hide(activeFragment).show(categoriesFragment).commit();
activeFragment = categoriesFragment;
return true;
case R.id.navigation_orders:
fm.beginTransaction().hide(activeFragment).show(ordersFragment).commit();
activeFragment = ordersFragment;
return true;
case R.id.navigation_profile:
fm.beginTransaction().hide(activeFragment).show(profileFragment).commit();
activeFragment = profileFragment;
return true;
case R.id.navigation_backup:
fm.beginTransaction().hide(activeFragment).show(backupFragment).commit();
activeFragment = backupFragment;
return true;
}
return false;
}
};
}
Вот фрагмент моей категории, который я хочу создать Tablayout внутри:
public class CategoriesFragment extends Fragment {
public CategoriesFragment() {
// Required empty public constructor
}
MyApi api = new MyApi();
TableLayout tabLayout;
ViewPager viewPager;
AdaptorViewPager adaptorViewPager;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_categories, container, false);
tabLayout = (TableLayout) getActivity().findViewById(R.id.tablayout_categories);
viewPager =(ViewPager) getActivity().findViewById(R.id.viewpager_category);
try{
api.createOrOpenDataBase(getActivity());
}catch (Exception e){
Toast.makeText(getActivity(),"failed to connect to database",Toast.LENGTH_SHORT);
}
SQLiteDatabase db= api.getDatabase();
int pagesCount = getCount(db);
String[] pageTitle = new String[pagesCount];
for(int i = 0;i<pagesCount;i++){
pageTitle[i] = getPageTitle(db,i);
}
Log.i("Log9","number of tabs is: " + pagesCount);
Log.i("Log9","tab names are: " + pageTitle.toString());
adaptorViewPager = new AdaptorViewPager(getActivity().getSupportFragmentManager(),pagesCount,pageTitle);
Log.i("Log9","adaptorViewPager is: " + adaptorViewPager.toString());
if(adaptorViewPager!=null) {
viewPager.setAdapter(adaptorViewPager);
tabLayout.addView(viewPager);
}
return view;
}
@Override
public void onResume() {
super.onResume();
Log.i("Log1","On resume");
//getCategories();
}
@Override
public void onPause() {
Log.i("Log1","on pause");
super.onPause();
}
private String getPageTitle(SQLiteDatabase db, int position) {
String pageTitle ="";
try{
String query = "SELECT * FROM firstcategory";
Cursor cursor = db.rawQuery(query,null);
cursor.moveToPosition(position);
pageTitle = cursor.getString(1);
Log.i("Log9","pageTitle is: " + pageTitle);
}catch (Exception e){
Log.i("Log9","can not respawn category name: " + e.toString());
}
return pageTitle;
}
private int getCount(SQLiteDatabase db) {
int pagesCount = 0;
Log.i("Log9", "Start counting ");
try{
String query ="SELECT * FROM firstcategory";
Cursor cursor = db.rawQuery(query,null);
while(cursor.moveToNext()){
pagesCount++;
}
Log.i("Log9","page count is: " + pagesCount);
}catch (Exception e){
Log.i("Log9","Cant Count ViewPagers Count: " + e.toString());
}
return pagesCount;
}
}
Это Fragment, который должен отображать информацию на каждой вкладке:
public class TabLayoutFragment extends Fragment {
private int position = 0;
public TabLayoutFragment(int pos) {
position = pos;
// Required empty public constructor
}
MyApi api = new MyApi();
Category category;
ArrayList<Category> categoryList = new ArrayList<>();
ListViewAdaptor adaptor;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
api.createOrOpenDataBase(getActivity());
Log.i("Log7","DataBase Opened Successfully");
View view = inflater.inflate(R.layout.fragment_tab_layout, container, false);
ListView listView = (ListView) getActivity().findViewById(R.id.category_list_item);
try {
String query = "SELECT * FROM firstcategory WHERE autoId = '" + position + "'";
Cursor cursor = api.getDatabase().rawQuery(query, null);
Log.i("Log7","cursor had made and fetched data");
cursor.moveToFirst();
Log.i("Log7","cursor moved to first successfully");
int child = cursor.getInt(5);
String parentid = cursor.getString(0);
int coded = Integer.parseInt(parentid);
coded = coded - 10;
if (child > 0) {
String query1 = "SELECT * FROM secondcategory WHERE parentid = '" + coded + "'";
Cursor cursor2 = api.getDatabase().rawQuery(query1, null);
Log.i("Log7","cursor1 created successfully");
while (cursor2.moveToNext()) {
String catTitle = cursor.getString(1);
byte[] byteImage = cursor.getBlob(2);
Bitmap catImage = BitmapFactory.decodeByteArray(byteImage, 0, byteImage.length);
String id = cursor.getString(6);
int children = cursor.getInt(8);
Category currentCategory = new Category(id, catTitle, catImage, children);
categoryList.add(currentCategory);
}
} else {
}
if(categoryList!=null){
adaptor = new ListViewAdaptor(getActivity(), categoryList);
Log.i("Log7","adaptor had made");
}else{
Log.i("Log7","adaptor did not made");
}
if(adaptor!=null) {
listView.setAdapter(adaptor);
Log.i("Log7","ListView had made");
}else{
Log.i("Log7","ListView did not made");
}
}catch (Exception e){
Log.i("Log7","Problem Reading tabs from db: " + e.toString());
}
return view;
}
public static TabLayoutFragment newInstance(int pos) {
Bundle args = new Bundle();
TabLayoutFragment fragment = new TabLayoutFragment(pos);
fragment.setArguments(args);
return fragment;
}
}
И последний, но не менее важный адаптер ViewPager:
public class AdaptorViewPager extends FragmentPagerAdapter {
SQLiteDatabase db;
int tabsNumber;
String[] tabNames;
public AdaptorViewPager(@NonNull FragmentManager fm,int tabCount,String[] tabnames) {
super(fm);
tabsNumber=tabCount;
tabNames = tabnames;
}
public AdaptorViewPager(@NonNull FragmentManager fm) {
super(fm);
}
@NonNull
@Override
public Fragment getItem(int position) {
Log.i("Log10", "Start StartFragments ");
if(position<0||position>position){
return null;
}
return TabLayoutFragment.newInstance(position);
}
//Count the numbers of pages in viewpagers
@Override
public int getCount() {
return tabsNumber;
}
@Nullable
@Override
public CharSequence getPageTitle(int position) {
String pageTitle =tabNames[position];
return pageTitle;
}
}
Данная ошибка:
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.esppad.fansy4, PID: 24898
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.esppad.fansy4/com.example.esppad.fansy4.Activities.HomeActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.viewpager.widget.ViewPager.setAdapter(androidx.viewpager.widget.PagerAdapter)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2778)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2856)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1589)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6494)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.viewpager.widget.ViewPager.setAdapter(androidx.viewpager.widget.PagerAdapter)' on a null object reference
at com.example.esppad.fansy4.fragments.CategoriesFragment.onCreateView(CategoriesFragment.java:53)
at androidx.fragment.app.Fragment.performCreateView(Fragment.java:2595)
at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:881)
at androidx.fragment.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManagerImpl.java:1238)
at androidx.fragment.app.BackStackRecord.executeOps(BackStackRecord.java:434)
at androidx.fragment.app.FragmentManagerImpl.executeOps(FragmentManagerImpl.java:2076)
at androidx.fragment.app.FragmentManagerImpl.executeOpsTogether(FragmentManagerImpl.java:1866)
at androidx.fragment.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManagerImpl.java:1821)
at androidx.fragment.app.FragmentManagerImpl.execPendingActions(FragmentManagerImpl.java:1727)
at androidx.fragment.app.FragmentManagerImpl.dispatchStateChange(FragmentManagerImpl.java:2660)
at androidx.fragment.app.FragmentManagerImpl.dispatchActivityCreated(FragmentManagerImpl.java:2610)
at androidx.fragment.app.FragmentController.dispatchActivityCreated(FragmentController.java:246)
at androidx.fragment.app.FragmentActivity.onStart(FragmentActivity.java:542)
at androidx.appcompat.app.AppCompatActivity.onStart(AppCompatActivity.java:201)
at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1334)
at android.app.Activity.performStart(Activity.java:7029)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2741)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2856)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1589)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6494)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)