如何使用带有片段的数据库

Question

 SQLiteDatabase db = getWritableDatabase();

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);
       }
    }

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 

下面是logcat：

12-15 13:15:30.763 295 33-29533/com.example.hieul.hismartversearch e/androidruntime：致命html" target="_blank">异常：main process：com.example.hieul.hismartversearch,pid：29533 java.lang.nullpointerexception：试图在Android.database.sqlite.sqlite.sqlite.sqlite.sqlite.sqlite.sqlite.sqlite.sqlite.sqlite.getdatabaseLocked（eOpenHelper.java:223)在Android.database.sqlite.sqliteOpenHelper.getWritableDatabase(SqliteOpenHelper.java:163)在com.example.hieul.hismartVersearch.db.queryData(Db.java:33)在com.example.hieul.hismartVersearch.tabonefragment.loaddTaWeb（Tabonefragment.java:309)在port.v4.app.FragmentManagerImpl.mo在Android.support.v4.app.fragmentManager.java:1419)在Android.support.v4.app.fragmentManagerimpl.moveFragmentToExpectedState（FragmentManager.java:1750)在Android.support.v4.app.fragmentManagerimpl.moveState（FragmentManager.java:1819)在Android.support.v4.app.fragmentManagerimpl.moveToState（FragmentManager.java:1819)在Android.support.v4.app.fragmentManagerImpl.removereddantOperationSandExecute(FragentManager.java:2332)，在Android.support.v4.app.fragmentManagerImpl.execsingleAction(FragmentManager.java:2209)，在Android.support.v4.app.backstackRecord.commitnoWollowingStateloss(BackstackRecord.java:649)，在4.view.viewpager.populate（viewpager.java:1086)在Android.support.v4.view.viewPager.onMeasure（viewPager.java:1616)在Android.view.view.measure（view.java:20151)在Android.view.viewgroup.measure（view.java:20151)在Android.view.viewgroup.measure ChildWith Margins（viewgroup.java:6328)在Android.support.design.widget.coordinatorlayout.onMeasurchild（port.design.widget.coordinatorlayout.onMeasure（coordinatorlayout.java:789)在Android.view.viewgroup.measure（view.java:20151)在Android.view.viewgroup.measure（view.java:20151)在Android.widget.line在Android.widget.v7.widget.framelayout.onMeasure（framelayout.java:194)在Android.widget.linearlayout.java:1464)android.widget.linearlayout.measurevertic(linearlayout.java:747)android.widget.linearlayout.onMeasur(linearlayout.java:629)android.View.viewgroup.measur(View.java:20151)android.View.viewgroup.measur(View.java:20151)android.View.View.measure（widget.linearlayout.MeasureChildbeRelayout(linearlayout.java:1464)，地址为Android.widget.linearlayout.measureVertic(linearlayout.java:747)，地址为Android.widget.linearlayout.onMeasure(linearlayout.java:629)，地址为Android.View.viewgroup.measure(View.java:20151)，地址为Android.View.viewgroup.measure(View.java:20151)，视图.java:20151)在Android.view.viewrootimpl.PerformMeasure（viewrootimpl.java:2594)在Android.vi

Answer 1

• 纠正您的片段节。
• 哪里是DBoncreate（SQLiteDatabase DB).

oncreate（SQLiteDatabase db)这是我们需要编写create table语句的地方。这在创建数据库时调用。

代码

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());

和

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