Help please solve the problem.

import android.database.Cursor; import android.os.Bundle; import android.app.Fragment; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.widget.ListView; import android.widget.SimpleCursorAdapter; import android.database.sqlite.SQLiteDatabase; public class FragmentСategoriesSecond extends Fragment implements View.OnClickListener { ListView userList; DatabaseHelper databaseHelper; SQLiteDatabase db; Cursor userCursor; SimpleCursorAdapter userAdapter; public FragmentCategoriesSecond() { } @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { super.onCreate(savedInstanceState); View v = inflater.inflate(R.layout.ex3, null); userList = (ListView)v.findViewById(R.id.list_item); databaseHelper = new DatabaseHelper(getActivity()); // создаем базу данных databaseHelper.create_db(); return v; } @Override public void onResume() { super.onResume(); // открываем подключение db = databaseHelper.open(); //получаем данные из бд в виде курсора userCursor = db.rawQuery("select * from "+ DatabaseHelper.TABLE, null); // определяем, какие столбцы из курсора будут выводиться в ListView String[] headers = new String[] {DatabaseHelper.COLUMN_NAME, DatabaseHelper.COLUMN_NAME}; // создаем адаптер, передаем в него курсор userAdapter = new SimpleCursorAdapter(getActivity(), android.R.layout.two_line_list_item, userCursor, headers, new int[]{android.R.id.text1, android.R.id.text2}, 0); userList.setAdapter(userAdapter); } @Override public void onDestroy(){ super.onDestroy(); // Закрываем подключение и курсор db.close(); userCursor.close(); } public void onClick(View v) { switch (v.getId()) { case R.id.button: { break; } case R.id.button1: { break; } } } }

An error

  --------- beginning of crash 2019-03-19 16:26:53.033 28931-28931/ru.forestcode.receptapp E/AndroidRuntime: FATAL EXCEPTION: main Process: ru.forestcode.receptapp, PID: 28931 java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference at ru.forestcode.receptapp.FragmentCategoriesSecond.onResume(FragmentCategoriesSecond.java:61) at android.app.Fragment.performResume(Fragment.java:2399) at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1032) at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1171) at android.app.BackStackRecord.run(BackStackRecord.java:815) at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1578) at android.app.FragmentManagerImpl$1.run(FragmentManager.java:483) at android.os.Handler.handleCallback(Handler.java:751) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:154) at android.app.ActivityThread.main(ActivityThread.java:6077) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)

    1 answer 1

    This means that you need to open the markup file ( ex3.xml ) and find that there is no <ListView> at all or it has a different id (not a list_item ) and correct the situation.

    That is, the reason for the error is that calling v.findViewById(R.id.list_item); did not find an element with such id and returned null .

    • Thank you very much! Eyes zamylilsya for the whole day and did not see the problem before the nose) - FerretBlack 1:51 pm