Android在Sqlite3中怎么应用

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1、首先先建立一个DatabaseHelper类，继承自SQLiteOpenHelper，用于建立数据库，并可更新数据库例如我新建了两张表

public class DatabaseHelper extends SQLiteOpenHelper {    private static DatabaseHelper _databaseHelper;    private static final String TAG = DatabaseHelper.class.getSimpleName();    public synchronized static DatabaseHelper getInstance(Context context)    {        if(_databaseHelper==null)        {            _databaseHelper = new DatabaseHelper(context,"cgjlb",null,2);        }        return _databaseHelper;    }    public synchronized static void destoryInstance(){        if(_databaseHelper!=null){            _databaseHelper=null;    public DatabaseHelper(@Nullable Context context, @Nullable String name, @Nullable SQLiteDatabase.CursorFactory factory, int version) {        super(context, name, factory, version);    @Override    public void onCreate(SQLiteDatabase sqLiteDatabase) {        //主表记录        String sql = "create table t_share(_id integer primary key autoincrement,sharenum text,sharename text,shareprice real,sharelastprice real,addtime text,uptime text,bl real)";        sqLiteDatabase.execSQL(sql);        //记录历史表        sql = "create table t_sharehis(_id integer primary key autoincrement,shareid integer, shareprice real,uptime text)";    public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {        Log.d(TAG, "onUpgrade: upddatabase");        sqLiteDatabase.execSQL("drop table t_share");        sqLiteDatabase.execSQL("drop table t_sharehis");        onCreate(sqLiteDatabase);}

2、编写数据库具体操作类、增删改查我都写了

public class ShareDbService {    SQLiteDatabase db = null;    DatabaseHelper databaseHelper;    private static final String TAG = ShareDbService.class.getSimpleName();    public ShareDbService(Context context) {        databaseHelper = DatabaseHelper.getInstance(context);        db = databaseHelper.getWritableDatabase();    }    public void addShareInfo(ShareBean shareBean)    {        int Id = getShareId(shareBean.getShareNum());        if(Id==-1) {            ContentValues values = new ContentValues();            values.put("sharenum", shareBean.getShareNum());            values.put("sharename", shareBean.getShareName());            values.put("shareprice", shareBean.getSharePrice());            values.put("sharelastprice", shareBean.getShareLastPrice());            values.put("uptime", shareBean.getUptime());            values.put("addtime",shareBean.getAddtime());            double shareprice = shareBean.getSharePrice();            double sharelastprice = shareBean.getShareLastPrice();            double bl = (sharelastprice-shareprice)/shareprice*100;            values.put("bl", new DecimalFormat("0.00").format(bl));            db = databaseHelper.getWritableDatabase();            db.insert("t_share", null, values);            ShareHisBean shareHisBean = new ShareHisBean();            shareHisBean.setShareId(getShareId(shareBean.getShareNum()));            shareHisBean.setSharePrice(shareBean.getSharePrice());            shareHisBean.setUpTime(shareBean.getUptime());            addShareHis(shareHisBean);            db.close();        }    private void addShareHis(ShareHisBean shareHisBean){        ContentValues values = new ContentValues();        values.put("shareid", shareHisBean.getShareId());        values.put("shareprice", shareHisBean.getSharePrice());        values.put("uptime", shareHisBean.getUptime());        db.insert("t_sharehis", null, values);        db.close();    public void refreshShare(ShareHisBean shareHisBean,double sharePrice){        try {            //更新信息主表            values.put("uptime", shareHisBean.getUptime());            values.put("sharelastprice", shareHisBean.getSharePrice());            String[] args = {String.valueOf(shareHisBean.getShareId())};            double sharelastprice = shareHisBean.getSharePrice();            double bl = (sharelastprice - sharePrice) / sharePrice * 100;            values.put("bl", bl);            db.update("t_share", values, "_Id=?", new String[]{String.valueOf(shareHisBean.getShareId())});            //添加记录            values = new ContentValues();            values.put("shareid", shareHisBean.getShareId());            values.put("shareprice", shareHisBean.getSharePrice());            db.insert("t_sharehis", null, values);        }catch(Exception ex){            ex.printStackTrace();        finally {    public void delShare(String Id){        db.delete("t_share","_Id=?",new String[]{Id});        db.delete("t_sharehis","shareid=?",new String[]{Id});    private int getShareId(String shareNum) {        db = databaseHelper.getReadableDatabase();        String sql = "select _Id from t_share where sharenum='" + shareNum + "'";        int Id = -1;        Cursor cursor = db.rawQuery(sql, null);        if (cursor != null) {            while (cursor.moveToNext()){                Id = cursor.getInt(0);            }        cursor.close();        return Id;    public List getShareList(){        List shareBeans = new ArrayList<>();        String sql = "select _id,sharenum,sharename,shareprice,sharelastprice,uptime,addtime,bl from t_share order by _Id desc";                ShareBean shareBean = new ShareBean();                shareBean.set_Id(cursor.getInt(0));                shareBean.setShareNum(cursor.getString(1));                shareBean.setShareName(cursor.getString(2));                shareBean.setSharePrice(cursor.getDouble(3));                shareBean.setShareLastPrice(cursor.getDouble(4));                shareBean.setUptime(cursor.getString(5));                shareBean.setAddtime(cursor.getString(6));                shareBean.setBl(cursor.getDouble(7));                shareBeans.add(shareBean);        return shareBeans;    public List getShareListHis(int ShareId){        List shareHisBeans = new ArrayList<>();        String sql = "select _id,shareid,shareprice,uptime from t_sharehis where shareid='"+String.valueOf(ShareId)+"' order by _id desc";                ShareHisBean shareHisBean = new ShareHisBean();                shareHisBean.set_Id(cursor.getInt(0));                shareHisBean.setShareId(cursor.getInt(1));                shareHisBean.setSharePrice(cursor.getDouble(2));                shareHisBean.setUpTime(cursor.getString(3));                shareHisBeans.add(shareHisBean);        return shareHisBeans;    public ShareBean getShareInfo(int ShareId) {        ShareBean shareBean = new ShareBean();        //_id integer primary key autoincrement,sharenum text,sharename text,shareprice real,sharelastprice real,addtime text,uptime text,bl real        String sql = "select _id,sharenum,sharename,shareprice,sharelastprice,addtime,uptime,bl from t_share where _Id='"+String.valueOf(ShareId)+"'";            if (cursor.moveToNext()){                shareBean.setAddtime(cursor.getString(5));                shareBean.setUptime(cursor.getString(6));        return shareBean;}

3、实际中的应用，就举一个例子吧，数据库操作不用开新线程，直接在主线程里弄就行

ShareDbService shareDbService = new ShareDbService(getContext()); shareDbService.delShare(String.valueOf(shareBean.get_Id()));

4、需要注意的是SQLite不支持多线程，最好是能批量修改，否则很麻烦，如果一定要多线程 ，比如循环请求网络更新数据库时，可以使用CountDownLatch，先将数据弄在一个集合里，等子线程全部执行完成后，再更新数据库。此方法具体应用如下

先声明一个变量

CountDownLatch latch;

实际应用代码

//设置多线程 个数，一共用多少个线程一定要写清楚，后面是要减的。        latch = new CountDownLatch(count);        for (int i = 0; i < count; i++) {                        new Thread(()-> {                try {                    //网络请求等操作                } catch (Exception e) {                    e.printStackTrace();                } finally {                    //这里会自动减1操作，一定要写。                    latch.countDown();                }            }).start();        };        try {            latch.await();           //最后执行主程序，比如更新数据库            Toast.makeText(getContext(), "刷新成功", Toast.LENGTH_SHORT).show();        } catch (InterruptedException e) {            e.printStackTrace();        }

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