【急】【关于Android 中SQLite的insert与query方法报错insert】。

Question

【关于Android 中SQLite的insert与query方法报错insert】
我觉得应该是SQLite相关操作的问题，但是找了很久找不到哪里报错。
代码是跟着网上一个项目的源码写的。这个项目没报错并且能正常运行，我一insert就报：

java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.Cursor android.database.sqlite.SQLiteDatabase.rawQuery(java.lang.String, java.lang.String[])' on a null object reference

找了78个小时都没找到

下面是logcat的报错信息

04-28 06:40:53.227 1344-1654/? W/audio_hw_generic: Not supplying enough data to HAL, expected position 14441882 , only wrote 14304701
04-28 06:40:56.113 1950-3104/com.android.inputmethod.latin D/EGL_emulation: eglMakeCurrent: 0xae4549c0: ver 3 1 (tinfo 0xae4524e0)
04-28 06:40:56.114 1950-3104/com.android.inputmethod.latin E/Surface: getSlotFromBufferLocked: unknown buffer: 0xa20fa0e0
04-28 06:40:57.874 9152-9152/com.example.nero.thecashregistersystem D/MyDBOpenHelper: query sql: select rowid,name,goods_number,in_price,out_price,'update_time 'from goods where name='123';
04-28 06:40:57.874 9152-9152/com.example.nero.thecashregistersystem D/AndroidRuntime: Shutting down VM


    --------- beginning of crash
04-28 06:40:57.874 9152-9152/com.example.nero.thecashregistersystem E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.nero.thecashregistersystem, PID: 9152
    java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.Cursor android.database.sqlite.SQLiteDatabase.rawQuery(java.lang.String, java.lang.String[])' on a null object reference
        at com.example.nero.thecashregistersystem.db.MyDBOpenHelper.query(MyDBOpenHelper.java:212)
        at com.example.nero.thecashregistersystem.db.MyDBOpenHelper.insert(MyDBOpenHelper.java:140)
        at com.example.nero.thecashregistersystem.db.MyDBOpenHelper.insert(MyDBOpenHelper.java:128)
        at com.example.nero.thecashregistersystem.add_goodsActivity.onClick(add_goodsActivity.java:108)
        at android.view.View.performClick(View.java:5198)
        at android.view.View$PerformClick.run(View.java:21147)
        at android.os.Handler.handleCallback(Handler.java:739)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:148)
        at android.app.ActivityThread.main(ActivityThread.java:5417)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

上代码：
MyDBOpenHelper.java

package com.example.nero.thecashregistersystem.db;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;

import com.example.nero.thecashregistersystem.bean.goodsInfo;
import com.example.nero.thecashregistersystem.bean.goodsInfo;

import java.util.ArrayList;

public class MyDBOpenHelper extends SQLiteOpenHelper {


    //from storage(这里是跟着项目源码敲的)
    private static final String TAG = "MyDBOpenHelper";
    private static final String DB_NAME = "my.db";
    private static MyDBOpenHelper mHelper = null;
    private SQLiteDatabase mDB = null;
    private static final String TABLE_NAME = "goods";
    private static final int DB_VERSION = 1;

    private MyDBOpenHelper(Context context) {
        super(context, DB_NAME, null, DB_VERSION);
    }

    private MyDBOpenHelper(Context context,int version) {
        super(context, DB_NAME, null, version);
    }

    @Override
    //数据库第一次创建时被调用
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("CREATE TABLE goods(good_ID INTEGER PRIMARY KEY AUTOINCREMENT," +
                "name VARCHAR(20)  NOT NULL," +
                "goods_number INTEGER NOT NULL," +
                "in_price REAL(8)  NOT NULL," +
                "out_price REAL(8)  NOT NULL," +
                "update_time VARCHAR NOT NULL)");
        db.execSQL("CREATE TABLE bill(bill_ID INTEGER PRIMARY KEY AUTOINCREMENT," +
                "name VARCHAR(20)," +
                "quantily INTEGER," +
                "goods_number INTEGER  NOT NULL," +
                "in_price REAL(8) NOT NULL," +
                "out_price REAL(8) NOT NULL ," +
                "sum_price REAL(8)," +
                "FOREIGN KEY(name) REFERENCES goods(name)," +
                "FOREIGN KEY(in_price) REFERENCES goods(in_price)," +
                "FOREIGN KEY(out_price) REFERENCES goods(out_price))");
        db.execSQL("CREATE TABLE orders(bill_ID INTEGER ,name VARCHAR(20)," +
                "quantily INTEGER ," +
                "goods_number INTEGER," +
                "out_price REAL(8)," +
                "sum_price REAL(8)," +
                "FOREIGN KEY(bill_ID) REFERENCES bill(bill_ID)," +
                "FOREIGN KEY(name) REFERENCES goods(name)," +
                "FOREIGN KEY(out_price) REFERENCES goods(out_price)," +
                "FOREIGN KEY(sum_price) REFERENCES bill(sum_price))");
    }

    //软件版本号发生改变时调用
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
//        db.execSQL("ALTER TABLE person ADD phone VARCHAR(12) NULL");
    }

    public static MyDBOpenHelper getInstance(Context context, int version) {
        if (version > 0 && mHelper == null) {
            mHelper = new MyDBOpenHelper(context, version);
        } else if (mHelper == null) {
            mHelper = new MyDBOpenHelper(context);
        }
        return mHelper;
    }

    public SQLiteDatabase openReadLink() {
        if (mDB == null || mDB.isOpen() != true) {
            mDB = mHelper.getReadableDatabase();
        }
        return mDB;
    }

    public SQLiteDatabase openWriteLink() {
        if (mDB == null || mDB.isOpen() != true) {
            mDB = mHelper.getWritableDatabase();
        }
        return mDB;
    }

    public void closeLink() {
        if (mDB != null && mDB.isOpen() == true) {
            mDB.close();
            mDB = null;
        }
    }

    public String getDBName() {
        if (mHelper != null) {
            return mHelper.getDatabaseName();
        } else {
            return DB_NAME;
        }
    }


    public int delete(String condition) {
        int count = mDB.delete(TABLE_NAME, condition, null);
        return count;
    }

    public int deleteAll() {
        int count = mDB.delete(TABLE_NAME, "1=1", null);
        return count;
    }


    public long insert(goodsInfo info) {
        ArrayList<goodsInfo> infoArray = new ArrayList<goodsInfo>();
        infoArray.add(info);
//这里的insert中的infoArray不为null，已经验证过了
//        if(infoArray == null){
//
//            Log.d("infoArray 为null","infoArray 为null");
//        }else {
//            Log.d("不为null","不为null");
//        }
        return insert(infoArray);//logcat报错中有提示到这行
    }

    public long insert(ArrayList<goodsInfo> infoArray) {
        long result = -1;
        for (int i = 0; i < infoArray.size(); i++) {
            goodsInfo info = infoArray.get(i);
            ArrayList<goodsInfo> tempArray = new ArrayList<goodsInfo>();
            // 如果存在同名记录，则更新记录
            // 注意条件语句的等号后面要用单引号括起来
            if (info.name != null && info.name.length() > 0) {
                String condition = String.format("name='%s'", info.name);
                tempArray = query(condition);
                if (tempArray.size() > 0) {
                    update(info, condition);
                    result = tempArray.get(0).rowid;
                    continue;
                }
            }
            // 如果存在同样的goods_number，则更新记录
            if (info.goods_number != null && info.goods_number.length() > 0) {
                String condition = String.format("goods_number='%s'", info.goods_number);
                tempArray = query(condition);//logcat报错中有提示到这行
                if (tempArray.size() > 0) {
                    update(info, condition);
                    result = tempArray.get(0).rowid;
                    continue;
                }
            }
            // 不存在唯一性重复的记录，则插入新记录
            ContentValues cv = new ContentValues();
            cv.put("name", info.name);
            cv.put("in_price", info.in_price);
            cv.put("out_price", info.out_price);
            cv.put("quantily", info.quantily);

            cv.put("update_time", info.update_time);

            result = mDB.insert(TABLE_NAME, "", cv);//logcat报错中有提示到这行
//            Log.d("这里result:"+result,"这里result:"+result);
//这里是Log.d没有打印

            // 添加成功后返回行号，失败后返回-1
            if (result == -1) {
                return result;
            }
        }
        return result;
    }

    public int update(goodsInfo info, String condition) {
        ContentValues cv = new ContentValues();
        cv.put("name", info.name);
        cv.put("in_price", info.in_price);
        cv.put("out_price", info.out_price);
        cv.put("quantily", info.quantily);
        cv.put("quantily", info.quantily);
        int count = mDB.update(TABLE_NAME, cv, condition, null);
        return count;
    }

    public int update(goodsInfo info) {
        return update(info, "rowid=" + info.rowid);
    }

    public ArrayList<goodsInfo> query(String condition) {
        String sql = String.format("select rowid,name,goods_number,in_price,out_price," +
//                "quantily,sum_price," +
                "'"+"update_time "+"'"+"from %s where %s;", TABLE_NAME, condition);
        Log.d(TAG, "query sql: " + sql);
        ArrayList<goodsInfo> infoArray = new ArrayList<goodsInfo>();
        Cursor cursor = mDB.rawQuery(sql, null);//logcat报错中有提示到这行
        if (cursor.moveToFirst()) {
            for (; ; cursor.moveToNext()) {
                goodsInfo info = new goodsInfo();
                info.rowid = cursor.getLong(0);
                info.goods_number = cursor.getString(0);
                info.in_price = cursor.getDouble(0);
                info.out_price = cursor.getDouble(0);
                info.quantily = cursor.getInt(0);
                info.sum_price = cursor.getDouble(0);

                if (cursor.isLast() == true) {
                    break;
                }
            }
        }
        cursor.close();
        return infoArray;
    }


//    }
}

在activity里的insert代码：

    @Override
    protected void onStart() {
        super.onStart();
        mHelper = MyDBOpenHelper.getInstance(this, 2);
        mHelper.openWriteLink();
    }

    @Override
    protected void onStop() {
        super.onStop();
        mHelper.closeLink();
    }


@Override
    public void onClick(View v) {
        if (v.getId() == R.id.button_addgoods) {
            String name = et_name.getText().toString();
            String goods_number = et_good_number.getText().toString();
            String in_price = et_in_price.getText().toString();
            String out_price = et_out_price.getText().toString();
            if (name==null || name.length()<=0) {
                showToast("请先填写商品名称");
                return;
            }
            if (goods_number==null || goods_number.length()<=0) {
                showToast("请先填写商品编码");
                return;
            }
            if (in_price==null || in_price.length()<=0) {
                showToast("请先填写进货价");
                return;
            }
            if (out_price==null || out_price.length()<=0) {
                showToast("请先填写出售价");
                return;
            }

            goodsInfo info = new goodsInfo();
            info.name = name;
            info.goods_number = goods_number;
            info.in_price = Long.parseLong(in_price);
            info.out_price = Float.parseFloat(out_price);
            info.update_time = DateUtil.getNowDateTime("yyyy-MM-dd HH:mm:ss");
            mHelper.insert(info);//logcat中提示到这行
            showToast("数据已写入SQLite数据库");
        }
    }

希望各位哥哥姐姐能告诉我哪里出错了。
（ps：如果有人愿意指导我这个project就更好了，这个project快弄完了，弄完数据库就弄个类似购物车 加减计算就ok了）

Answer 1

你Debug一下看看，mDB初始化成功了吗，是不是null？