How to use database with fragment

1
votes

I am using an Activity manager tab layout that has three fragments. I call class Db extends SQLiteHelper in TabtOneFragment but it is not working and shows this error at Line in Db file. 

 SQLiteDatabase db = getWritableDatabase();

I'm using Db db = new Db(getActivity()); to get context but it isn't working either. Any help would be super helpful, Please!

Here is the Db class:

package com.example.hismartversearch;

import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class Db extends SQLiteOpenHelper {
    public Db(Context context) {
        super(context, "Db.sqlite", null, 1);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
    }

    public Cursor getdata(String sql) {
        // error at this line below
        SQLiteDatabase db = getWritableDatabase();
        Cursor c = db.rawQuery(sql, null);
        return c;
    }

    public void querydata(String sql) {
        SQLiteDatabase db = getWritableDatabase();
        db.execSQL(sql);
    }

    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    }

    public void delete_table(String table_name) {
        SQLiteDatabase db = getWritableDatabase();
        db.execSQL("delete from " + table_name);
    }

    public void delete_row(String tenbang, String tencot, String giatri) {
        SQLiteDatabase db = getWritableDatabase();
        db.delete(tenbang, tencot + "=" + giatri, null);
       }
    }

Here is TabOneFragment : 

public class TabOneFragment extends Fragment implements SearchView.OnQueryTextListener {
Db db = new Db(getActivity());
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.tab_one_fragment, container, false);
        recyclerView = (RecyclerView) view.findViewById(R.id.recyclerview);
 final RecyclerView.LayoutManager mLayoutManager = new GridLayoutManager(getActivity(), 2);
        recyclerView.setLayoutManager(mLayoutManager);
        recyclerView.addItemDecoration(new GridSpacingItemDecoration(2, dpToPx(5), true));
        recyclerView.setItemAnimator(new DefaultItemAnimator());
        recyclerView.setAdapter(adapter);
   return view;
    }

    @Override
    public boolean onQueryTextSubmit(String query) {
        return false;
    }

    @Override
    public boolean onQueryTextChange(String newText) {
        return false;
    }

// error at line in logcat when I create table. 

 public void LoadDtaWeb() {
      db.querydata("Create table if not exists tbl_mon_app (_ID integer primary key, IDMon integer not null, IDCH integer not null, TenMon text not null, Gia text not null, ImgUrl text not null, ImgLocal text)");
    }
}
//some text hidden to save space display

Here is Logcat:

12-15 13:15:30.763 29533-29533/com.example.hieul.hismartversearch E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.hieul.hismartversearch, PID: 29533 java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.sqlite.SQLiteDatabase android.content.Context.openOrCreateDatabase(java.lang.String, int, android.database.sqlite.SQLiteDatabase$CursorFactory, android.database.DatabaseErrorHandler)' on a null object reference at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:223) at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:163) at com.example.hieul.hismartversearch.Db.querydata(Db.java:33) at com.example.hieul.hismartversearch.TabOneFragment.LoadDtaWeb(TabOneFragment.java:309) at com.example.hieul.hismartversearch.TabOneFragment.onCreateView(TabOneFragment.java:131) at android.support.v4.app.Fragment.performCreateView(Fragment.java:2261) at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1419) at android.support.v4.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManager.java:1750) at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1819) at android.support.v4.app.BackStackRecord.executeOps(BackStackRecord.java:797) at android.support.v4.app.FragmentManagerImpl.executeOps(FragmentManager.java:2590) at android.support.v4.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2377) at android.support.v4.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManager.java:2332) at android.support.v4.app.FragmentManagerImpl.execSingleAction(FragmentManager.java:2209) at android.support.v4.app.BackStackRecord.commitNowAllowingStateLoss(BackStackRecord.java:649) at android.support.v4.app.FragmentStatePagerAdapter.finishUpdate(FragmentStatePagerAdapter.java:167) at android.support.v4.view.ViewPager.populate(ViewPager.java:1238) at android.support.v4.view.ViewPager.populate(ViewPager.java:1086) at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1616) at android.view.View.measure(View.java:20151) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6328) at android.support.design.widget.CoordinatorLayout.onMeasureChild(CoordinatorLayout.java:719) at android.support.design.widget.HeaderScrollingViewBehavior.onMeasureChild(HeaderScrollingViewBehavior.java:91) at android.support.design.widget.AppBarLayout$ScrollingViewBehavior.onMeasureChild(AppBarLayout.java:1361) at android.support.design.widget.CoordinatorLayout.onMeasure(CoordinatorLayout.java:789) at android.view.View.measure(View.java:20151) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6328) at android.widget.FrameLayout.onMeasure(FrameLayout.java:194) at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:139) at android.view.View.measure(View.java:20151) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6328) at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1464) at android.widget.LinearLayout.measureVertical(LinearLayout.java:747) at android.widget.LinearLayout.onMeasure(LinearLayout.java:629) at android.view.View.measure(View.java:20151) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6328) at android.widget.FrameLayout.onMeasure(FrameLayout.java:194) at android.view.View.measure(View.java:20151) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6328) at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1464) at android.widget.LinearLayout.measureVertical(LinearLayout.java:747) at android.widget.LinearLayout.onMeasure(LinearLayout.java:629) at android.view.View.measure(View.java:20151) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6328) at android.widget.FrameLayout.onMeasure(FrameLayout.java:194) at com.android.internal.policy.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:3143) at android.view.View.measure(View.java:20151) at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2594) at android.vi

2
androidsqlitefragmentandroid-sqlite
Possible duplicate of Opening Android Sqlite Database in Fragment – Benjith binja

2 Answers

3
votes
  • Rectify your FRAGMENT section.
  • Where is DB onCreate(SQLiteDatabase db).

onCreate(SQLiteDatabase db) These is where we need to write create table statements. This is called when database is created.

Code

public class TabOneFragment extends Fragment implements SearchView.OnQueryTextListener {
public Db db ;

   @Override
    public void onCreate(Bundle savedInstanceState) 
    {
        super.onCreate(savedInstanceState);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        View view = inflater.inflate(R.layout.tab_one_fragment, container, false);
        db = new Db(getActivity());

And 

@Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(CREATE_TABLE_STATEMENT);
    }

Check Android SQLite Database Tutorial.

0
votes
public static final String TABLE_NAME = "table_name";   

 String CREATE_TABLE_SAMPLE = "create table " + TABLE_NAME + " (" + COLUMN_XXX_ID + " UNIQUE,"
                + COLUMN_XXX_NAME + "," + COLUMN_XXXX +
                "," + COLUMN_XXXXX + ");";


        @Override
        public void onCreate(SQLiteDatabase db) {
            db.execSQL(CREATE_TABLE_SAMPLE);
        }

        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
            db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
            onCreate(db);
        }