java - .SQLiteCantOpenDatabaseException : unknown error (code 14): Could not open database

Question

我在打开 SQLite 数据库时遇到问题。它向我显示错误(代码 14)无法打开数据库。我已经尝试过针对先前提出的问题的解决方案，但没有帮助。我已经尝试检查数据库文件是否存在，我也添加了读写权限，但它仍然给我这些错误。我只想知道我做错了什么。请告诉我。

DBHelper.java

    import java.io.File;
    import java.io.FileOutputStream;
    import java.io.IOException;
    import java.io.InputStream;
    import java.io.OutputStream;
    import java.util.ArrayList;
    import android.content.ContentValues;
    import android.content.Context;
    import android.database.Cursor;
    import android.database.SQLException;
    import android.database.sqlite.SQLiteDatabase;
    import android.database.sqlite.SQLiteOpenHelper;
    import android.util.Log;
    public class DBHelper extends SQLiteOpenHelper {
        String DB_PATH;
        private final static String DB_NAME = "db_order";
        public final static int DB_VERSION = 1;
        public static SQLiteDatabase db;

        private final Context context;

        private final String TABLE_NAME = "tbl_order";
        private final String ID = "id";
        private final String MENU_NAME = "Menu_name";
        private final String QUANTITY = "Quantity";
        private final String TOTAL_PRICE = "Total_price";


        public DBHelper(Context context) {

            super(context, DB_NAME, null, DB_VERSION);
            this.context = context;

            DB_PATH = Constant.DBPath;
        }

        public void createDataBase() throws IOException {

            boolean dbExist = checkDataBase();
            SQLiteDatabase db_Read = null;


            if (dbExist) {
                //do nothing - database already exist

            } else {
                db_Read = this.getReadableDatabase();
                db_Read.close();

                try {
                    copyDataBase();
                } catch (IOException e) {
                    throw new Error("Error copying database");
                }
            }

        }


    private boolean checkDataBase() {

        File dbFile = new File(DB_PATH + DB_NAME);

        return dbFile.exists();

    }


    private void copyDataBase() throws IOException {

        InputStream myInput = context.getAssets().open(DB_NAME);

        String outFileName = DB_PATH + DB_NAME;

        OutputStream myOutput = new FileOutputStream(outFileName);

        byte[] buffer = new byte[1024];
        int length;
        while ((length = myInput.read(buffer)) > 0) {
            myOutput.write(buffer, 0, length);
        }

        myOutput.flush();
        myOutput.close();
        myInput.close();

    }

    public void openDataBase() throws SQLException {
        SQLiteDatabase db = null;
        try {

            String myPath = DB_PATH + DB_NAME;
            File file = new File(myPath);
            if (file.exists() && !file.isDirectory()) {
                db = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE);
            }


            if (db != null) {
                db.close();
            }

        }catch (SQLException e)
        {
          //
        }
        if(db!= null)
        {
            db.close();
        }
    }
    @Override
    public void close() {
        db.close();
    }

    @Override
    public void onCreate(SQLiteDatabase db) {

    }

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

    /** this code is used to get all data from database */
    public ArrayList<ArrayList<Object>> getAllData(){
        ArrayList<ArrayList<Object>> dataArrays = new ArrayList<ArrayList<Object>>();

        Cursor cursor = null;

            try{
                cursor = db.query(
                        TABLE_NAME,
                        new String[]{ID, MENU_NAME, QUANTITY, TOTAL_PRICE},
                        null,null, null, null, null);
                cursor.moveToFirst();

                if (!cursor.isAfterLast()){
                    do{
                        ArrayList<Object> dataList = new ArrayList<Object>();

                        dataList.add(cursor.getLong(0));
                        dataList.add(cursor.getString(1));
                        dataList.add(cursor.getString(2));
                        dataList.add(cursor.getString(3));

                        dataArrays.add(dataList);
                    }

                    while (cursor.moveToNext());
                }
                cursor.close();
            }catch (SQLException e){
                Log.e("DB Error", e.toString());
                e.printStackTrace();
            }

        return dataArrays;
    }

    /** this code is used to get all data from database */
    public boolean isDataExist(long id){
        boolean exist = false;

        Cursor cursor = null;

            try{
                cursor = db.query(
                        TABLE_NAME,
                        new String[]{ID},
                        ID +"="+id,
                        null, null, null, null);
                if(cursor.getCount() > 0){
                    exist = true;
                }

                cursor.close();
            }catch (SQLException e){
                Log.e("DB Error", e.toString());
                e.printStackTrace();
            }

        return exist;
    }

    /** this code is used to get all data from database */
    public boolean isPreviousDataExist(){
        boolean exist = false;

        Cursor cursor;


            try{
                cursor = db.query(
                        TABLE_NAME,
                        new String[]{ID},
                        null,null, null, null, null);
                if(cursor.getCount() > 0){
                    exist = true;
                }

                cursor.close();
            }catch (SQLException e){
                Log.e("DB Error", e.toString());
                e.printStackTrace();
            }

        return exist;
    }

    public void addData(long id, String menu_name, int quantity, double total_price){
        // this is a key value pair holder used by android's SQLite functions
        ContentValues values = new ContentValues();
        values.put(ID, id);
        values.put(MENU_NAME, menu_name);
        values.put(QUANTITY, quantity);
        values.put(TOTAL_PRICE, total_price);

        // ask the database object to insert the new data 
        try{db.insert(TABLE_NAME, null, values);}
        catch(Exception e)
        {
            Log.e("DB ERROR", e.toString());
            e.printStackTrace();
        }
    }

    public void deleteData(long id){
        // ask the database manager to delete the row of given id
        try {db.delete(TABLE_NAME, ID + "=" + id, null);}
        catch (Exception e)
        {
            Log.e("DB ERROR", e.toString());
            e.printStackTrace();
        }
    }

    public void deleteAllData(){
        // ask the database manager to delete the row of given id
        try {db.delete(TABLE_NAME, null, null);}
        catch (Exception e)
        {
            Log.e("DB ERROR", e.toString());
            e.printStackTrace();
        }
    }

    public void updateData(long id, int quantity, double total_price){
        // this is a key value pair holder used by android's SQLite functions
        ContentValues values = new ContentValues();
        values.put(QUANTITY, quantity);
        values.put(TOTAL_PRICE, total_price);

        // ask the database object to update the database row of given rowID
        try {db.update(TABLE_NAME, values, ID + "=" + id, null);}
        catch (Exception e)
        {
            Log.e("DB Error", e.toString());
            e.printStackTrace();
        }
    }
}

主 Activity .java

package com.solodroid.frizzy;

import java.io.IOException;
import java.util.ArrayList;

import com.parse.Parse;
import com.parse.ParseAnalytics;
import com.parse.ParseInstallation;
import com.parse.PushService;

import android.annotation.SuppressLint;
import android.app.ActionBar;
import android.app.AlertDialog;
import android.app.Fragment;
import android.content.DialogInterface;
import android.content.Intent;
import android.content.res.Configuration;
import android.content.res.TypedArray;
import android.database.SQLException;
import android.graphics.drawable.ColorDrawable;
import android.net.Uri;
import android.os.Bundle;
import android.support.v4.app.ActionBarDrawerToggle;
import android.support.v4.app.FragmentActivity;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.util.DisplayMetrics;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ListView;
import android.widget.Toast;

@SuppressLint("NewApi")
public class MainActivity extends FragmentActivity {
    private DrawerLayout mDrawerLayout;
    private ListView mDrawerList;
    private ActionBarDrawerToggle mDrawerToggle;

    // nav drawer title
    private CharSequence mDrawerTitle;

    // used to store app title
    private CharSequence mTitle;

    // slide menu items
    private String[] navMenuTitles;
    private TypedArray navMenuIcons;

    private ArrayList<NavDrawerItem> navDrawerItems;
    private AdapterNavDrawerList adapter;

    // declare dbhelper and adapter object
    static DBHelper dbhelper;
    AdapterMainMenu mma;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.nav_drawer_main);

        // Parse push notification
        Parse.initialize(this, getString(R.string.parse_application_id), getString(R.string.parse_client_key));
        ParseAnalytics.trackAppOpened(getIntent());
        PushService.setDefaultPushCallback(this, MainActivity.class);
        ParseInstallation.getCurrentInstallation().saveInBackground();

        mTitle = mDrawerTitle = getTitle();

        // load slide menu items
        navMenuTitles = getResources().getStringArray(R.array.nav_drawer_items);

        // nav drawer icons from resources
        navMenuIcons = getResources().obtainTypedArray(R.array.nav_drawer_icons);

        mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
        mDrawerList = (ListView) findViewById(R.id.list_slidermenu);

        mDrawerLayout.setDrawerShadow(R.drawable.navigation_drawer_shadow, GravityCompat.START);

        navDrawerItems = new ArrayList<NavDrawerItem>();

        // adding nav drawer items to array
        navDrawerItems.add(new NavDrawerItem(navMenuTitles[0], navMenuIcons.getResourceId(0, -1)));

        navDrawerItems.add(new NavDrawerItem(navMenuTitles[1], navMenuIcons.getResourceId(1, -1)));
        navDrawerItems.add(new NavDrawerItem(navMenuTitles[2], navMenuIcons.getResourceId(2, -1)));
        navDrawerItems.add(new NavDrawerItem(navMenuTitles[3], navMenuIcons.getResourceId(3, -1)));

        navDrawerItems.add(new NavDrawerItem(navMenuTitles[4], navMenuIcons.getResourceId(4, -1)));
        navDrawerItems.add(new NavDrawerItem(navMenuTitles[5], navMenuIcons.getResourceId(5, -1)));
        navDrawerItems.add(new NavDrawerItem(navMenuTitles[6], navMenuIcons.getResourceId(6, -1)));

        navDrawerItems.add(new NavDrawerItem(navMenuTitles[7], navMenuIcons.getResourceId(7, -1)));
        navDrawerItems.add(new NavDrawerItem(navMenuTitles[8], navMenuIcons.getResourceId(8, -1)));
        navDrawerItems.add(new NavDrawerItem(navMenuTitles[9], navMenuIcons.getResourceId(9, -1)));

        // Recycle the typed array
        navMenuIcons.recycle();

        mDrawerList.setOnItemClickListener(new SlideMenuClickListener());

        // setting the nav drawer list adapter
        adapter = new AdapterNavDrawerList(getApplicationContext(), navDrawerItems);
        mDrawerList.setAdapter(adapter);

        // enabling action bar app icon and behaving it as toggle button
        //getActionBar().setDisplayHomeAsUpEnabled(true);
        //getActionBar().setHomeButtonEnabled(true);

        ActionBar bar = getActionBar();
        //bar.setBackgroundDrawable(new ColorDrawable(getResources().getColor(R.color.header)));

        // get screen device width and height
        DisplayMetrics dm = new DisplayMetrics();
        getWindowManager().getDefaultDisplay().getMetrics(dm);

        // checking internet connection
        if (!Constant.isNetworkAvailable(MainActivity.this)) {
            Toast.makeText(MainActivity.this, getString(R.string.no_internet), Toast.LENGTH_SHORT).show();
        }

        mma = new AdapterMainMenu(this);
        dbhelper = new DBHelper(this);

        // create database
        try {
            dbhelper.createDataBase();
        } catch (IOException ioe) {
            throw new Error("Unable to create database");
        }

        // then, the database will be open to use
        try {
            dbhelper.getWritableDatabase();
            dbhelper.openDataBase();
        } catch (SQLException sqle) {
            throw sqle;
        }

        // if user has already ordered food previously then show confirm dialog
        if (dbhelper.isPreviousDataExist()) {
            showAlertDialog();
        }

        mDrawerToggle = new ActionBarDrawerToggle(this, mDrawerLayout, R.drawable.ic_drawer, // nav
                // menu
                // toggle
                // icon
                R.string.app_name, // nav drawer open - description for
                // accessibility
                R.string.app_name // nav drawer close - description for
                // accessibility
        ) {
            public void onDrawerClosed(View view) {
                getActionBar().setTitle(mTitle);
                // calling onPrepareOptionsMenu() to show action bar icons
                invalidateOptionsMenu();
            }

            public void onDrawerOpened(View drawerView) {
                getActionBar().setTitle(mDrawerTitle);
                // calling onPrepareOptionsMenu() to hide action bar icons
                invalidateOptionsMenu();
            }
        };
        mDrawerLayout.setDrawerListener(mDrawerToggle);

        if (savedInstanceState == null) {
            // on first time display view for first nav item
            displayView(0);
        }
    }

    // show confirm dialog to ask user to delete previous order or not
    void showAlertDialog() {
        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder.setTitle(R.string.confirm);
        builder.setMessage(getString(R.string.db_exist_alert));
        builder.setCancelable(false);
        builder.setPositiveButton(getString(R.string.yes), new DialogInterface.OnClickListener() {

            public void onClick(DialogInterface dialog, int which) {
                // TODO Auto-generated method stub
                // delete order data when yes button clicked
                dbhelper.deleteAllData();
                dbhelper.close();

            }
        });

        builder.setNegativeButton(getString(R.string.no), new DialogInterface.OnClickListener() {

            public void onClick(DialogInterface dialog, int which) {
                // TODO Auto-generated method stub
                // close dialog when no button clicked
                dbhelper.close();
                dialog.cancel();
            }
        });
        AlertDialog alert = builder.create();
        alert.show();

    }

    @Override
    public void onBackPressed() {
        // TODO Auto-generated method stub
        dbhelper.deleteAllData();
        dbhelper.close();
        finish();
        overridePendingTransition(R.anim.open_main, R.anim.close_next);
    }

    /**
     * Slide menu item click listener
     */
    private class SlideMenuClickListener implements ListView.OnItemClickListener {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            // display view for selected nav drawer item
            displayView(position);
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // toggle nav drawer on selecting action bar app icon/title
        if (mDrawerToggle.onOptionsItemSelected(item)) {
            return true;
        }
        // Handle action bar actions click
        switch (item.getItemId()) {
            case R.id.rate_app:
                try {
                    startActivity(new Intent(Intent.ACTION_VIEW, Uri.parse("market://details?id=" + getPackageName())));
                } catch (android.content.ActivityNotFoundException anfe) {
                    startActivity(new Intent(Intent.ACTION_VIEW,
                            Uri.parse("http://play.google.com/store/apps/details?id=" + getPackageName())));
                }
                return true;
            case R.id.more_app:
                startActivity(new Intent(Intent.ACTION_VIEW, Uri.parse(getString(R.string.more_apps))));
                return true;
            default:
                return super.onOptionsItemSelected(item);
        }
    }

    /*
     * * Called when invalidateOptionsMenu() is triggered
     */
    @Override
    public boolean onPrepareOptionsMenu(Menu menu) {
        // if nav drawer is opened, hide the action items
        boolean drawerOpen = mDrawerLayout.isDrawerOpen(mDrawerList);
        menu.findItem(R.id.ic_menu).setVisible(!drawerOpen);
        return super.onPrepareOptionsMenu(menu);
    }

    /**
     * Diplaying fragment view for selected nav drawer list item
     */
    private void displayView(int position) {
        // update the main content by replacing fragments
        Fragment fragment = null;
        switch (position) {
            case 0:
                fragment = new ActivityHome();
                break;
            case 1:
                startActivity(new Intent(getApplicationContext(), ActivityCategoryList.class));
                overridePendingTransition(R.anim.open_next, R.anim.close_next);
                break;
            case 2:
                startActivity(new Intent(getApplicationContext(), ActivityCart.class));
                overridePendingTransition(R.anim.open_next, R.anim.close_next);
                break;
            case 3:
                startActivity(new Intent(getApplicationContext(), ActivityCheckout.class));
                overridePendingTransition(R.anim.open_next, R.anim.close_next);
                break;
            case 4:
                startActivity(new Intent(getApplicationContext(), ActivityProfile.class));
                overridePendingTransition(R.anim.open_next, R.anim.close_next);
                break;
            case 5:
                startActivity(new Intent(getApplicationContext(), ActivityInformation.class));
                overridePendingTransition(R.anim.open_next, R.anim.close_next);
                break;
            case 6:
                startActivity(new Intent(getApplicationContext(), ActivityAbout.class));
                overridePendingTransition(R.anim.open_next, R.anim.close_next);

                break;
            case 7:
                Intent sendInt = new Intent(Intent.ACTION_SEND);
                sendInt.putExtra(Intent.EXTRA_SUBJECT, getString(R.string.app_name));
                sendInt.putExtra(Intent.EXTRA_TEXT, "E-Commerce Android App\n\"" + getString(R.string.app_name)
                        + "\" \nhttps://play.google.com/store/apps/details?id=" + getPackageName());
                sendInt.setType("text/plain");
                startActivity(Intent.createChooser(sendInt, "Share"));
                break;
            case 8:
                startActivity(new Intent(getApplicationContext(), ActivityContactUs.class));
                overridePendingTransition(R.anim.open_next, R.anim.close_next);

                break;
            case 9:
                dbhelper.deleteAllData();
                dbhelper.close();
                MainActivity.this.finish();
                overridePendingTransition(R.anim.open_next, R.anim.close_next);

                break;

            default:
                break;
        }

        if (fragment != null) {
            android.app.FragmentManager fragmentManager = getFragmentManager();
            fragmentManager.beginTransaction().replace(R.id.frame_container, fragment).commit();

            // update selected item and title, then close the drawer
            mDrawerList.setItemChecked(position, true);
            mDrawerList.setSelection(position);
            setTitle(navMenuTitles[position]);
            mDrawerLayout.closeDrawer(mDrawerList);
        } else {
            // error in creating fragment
            Log.e("MainActivity", "Error in creating fragment");
        }
    }

    @Override
    public void setTitle(CharSequence title) {
        mTitle = title;
        getActionBar().setTitle(mTitle);
    }

    /**
     * When using the ActionBarDrawerToggle, you must call it during
     * onPostCreate() and onConfigurationChanged()...
     */

    @Override
    protected void onPostCreate(Bundle savedInstanceState) {
        super.onPostCreate(savedInstanceState);
        // Sync the toggle state after onRestoreInstanceState has occurred.
        mDrawerToggle.syncState();
    }

    @Override
    public void onConfigurationChanged(Configuration newConfig) {
        super.onConfigurationChanged(newConfig);
        // Pass any configuration change to the drawer toggls
        mDrawerToggle.onConfigurationChanged(newConfig);
    }

}

日志:

09-19 01:59:06.747 17250-17250/com.solodroid.frizzy E/SQLiteLog: (14) cannot open file at line 32456 of [bda77dda96]
09-19 01:59:06.747 17250-17250/com.solodroid.frizzy E/SQLiteLog: (14) os_unix.c:32456: (13) open(/data/data/com.solodroid.ecommerce/databases/db_order) - 
09-19 01:59:06.748 17250-17250/com.solodroid.frizzy E/SQLiteDatabase: Failed to open database '/data/data/com.solodroid.ecommerce/databases/db_order'.
   android.database.sqlite.SQLiteCantOpenDatabaseException: unknown error (code 14): Could not open database
        at android.database.sqlite.SQLiteConnection.nativeOpen(Native Method)
       at android.database.sqlite.SQLiteConnection.open(SQLiteConnection.java:209)
        at android.database.sqlite.SQLiteConnection.open(SQLiteConnection.java:193)
        at android.database.sqlite.SQLiteConnectionPool.openConnectionLocked(SQLiteConnectionPool.java:463)
        at android.database.sqlite.SQLiteConnectionPool.open(SQLiteConnectionPool.java:185)
        at android.database.sqlite.SQLiteConnectionPool.open(SQLiteConnectionPool.java:177)
        at android.database.sqlite.SQLiteDatabase.openInner(SQLiteDatabase.java:808)
        at android.database.sqlite.SQLiteDatabase.open(SQLiteDatabase.java:793)
        at android.database.sqlite.SQLiteDatabase.openDatabase(SQLiteDatabase.java:696)
        at android.database.sqlite.SQLiteDatabase.openDatabase(SQLiteDatabase.java:671)
        at com.solodroid.frizzy.DBHelper.openDataBase(DBHelper.java:101)
        at com.solodroid.frizzy.MainActivity.onCreate(MainActivity.java:138)
        at android.app.Activity.performCreate(Activity.java:6662)
                  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2599)
  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
  at android.app.ActivityThread.-wrap12(ActivityThread.java)
  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
  at android.os.Handler.dispatchMessage(Handler.java:102)
  at android.os.Looper.loop(Looper.java:154)
  at android.app.ActivityThread.main(ActivityThread.java:6077)
  at java.lang.reflect.Method.invoke(Native Method)
  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
                                                                                    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)
09-19 01:59:06.748 17250-17250/com.solodroid.frizzy D/AndroidRuntime: Shutting down VM
09-19 01:59:06.748 17250-17250/com.solodroid.frizzy E/AndroidRuntime: FATAL EXCEPTION: main
   Process: com.solodroid.frizzy, PID: 17250
   java.lang.RuntimeException: Unable to start activity ComponentInfo{com.solodroid.frizzy/com.solodroid.frizzy.MainActivity}:
   java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.Cursor android.database.sqlite.SQLiteDatabase.query(java.lang.String, java.lang.String[],
   java.lang.String, java.lang.String[], java.lang.String, java.lang.String, java.lang.String)' on a null object reference
       at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2646)
       at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
       at android.app.ActivityThread.-wrap12(ActivityThread.java)
       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
       at android.os.Handler.dispatchMessage(Handler.java:102)
       at android.os.Looper.loop(Looper.java:154)
       at android.app.ActivityThread.ma

              in(ActivityThread.java:6077)
                                                                                  at java.lang.reflect.Method.invoke(Native Method)
  com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)
  Caused by: java.lang.NullPointerException: 
  Attempt to invoke virtual method 'android.database.Cursor android.database.sqlite.SQLiteDatabase.query(java.lang.String, java.lang.String[], java.lang.String, java.lang.String[], java.lang.String, java.lang.String, java.lang.String)'
  on a null object reference
  at com.solodroid.frizzy.DBHelper.isPreviousDataExist(DBHelper.java:205)
  at com.solodroid.frizzy.MainActivity.onCreate(MainActivity.java:144)
  at android.app.Activity.performCreate(Activity.java:6662)
  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2599)
  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707) 
  at android.app.ActivityThread.-wrap12(ActivityThread.java) 
  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)   at android.os.Handler.dispatchMessage(Handler.java:102)
  at android.os.Looper.loop(Looper.java:154) 
  at android.app.ActivityThread.main(ActivityThread.java:6077) 
  at java.lang.reflect.Method.invoke(Native Method)

Answer 1

您永远不会打开 db在您的 DBHelper.isPreviousDataExist() 中引用方法。它引用全局静态 db :

DBHelper.java

public static SQLiteDatabase db

您可以使它成为一个实例变量并在构造函数中初始化它(首选)，或者完全摆脱它并创建一个本地 SQLiteDatabase在你的DBHelper.isPreviousDataExist()方法，就像您在其他方法中所做的那样。

最后，您的代码有很多问题，但是 public static成员是一个很大的代码味道。 See this为什么。