Android在Sqlite3中的应用及多线程使用数据库的建议

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)";
        sqLiteDatabase.execSQL(sql);
    }

    @Override
    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 = databaseHelper.getWritableDatabase();
        db.insert("t_sharehis", null, values);
        db.close();
    }

    public void refreshShare(ShareHisBean shareHisBean,double sharePrice){
        try {
            //更新信息主表
            db = databaseHelper.getWritableDatabase();
            ContentValues values = new ContentValues();
            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());
            values.put("uptime", shareHisBean.getUptime());
            db.insert("t_sharehis", null, values);
        }catch(Exception ex){
            ex.printStackTrace();
        }
        finally {
            db.close();
        }

    }

    public void delShare(String Id){
        db = databaseHelper.getWritableDatabase();
        db.delete("t_share","_Id=?",new String[]{Id});
        db.delete("t_sharehis","shareid=?",new String[]{Id});
        db.close();
    }

    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();
        db.close();
        return Id;
    }

    public List<ShareBean> getShareList(){
        db = databaseHelper.getReadableDatabase();
        List<ShareBean> shareBeans = new ArrayList<>();
        String sql = "select _id,sharenum,sharename,shareprice,sharelastprice,uptime,addtime,bl from t_share order by _Id desc";
        Cursor cursor = db.rawQuery(sql, null);
        if (cursor != null) {
            while (cursor.moveToNext()){
                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);
            }
        }
        cursor.close();
        db.close();
        return shareBeans;
    }

    public List<ShareHisBean> getShareListHis(int ShareId){
        db = databaseHelper.getReadableDatabase();
        List<ShareHisBean> shareHisBeans = new ArrayList<>();
        String sql = "select _id,shareid,shareprice,uptime from t_sharehis where shareid='"+String.valueOf(ShareId)+"' order by _id desc";
        Cursor cursor = db.rawQuery(sql, null);
        if (cursor != null) {
            while (cursor.moveToNext()){
                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);
            }
        }
        cursor.close();
        db.close();
        return shareHisBeans;
    }

    public ShareBean getShareInfo(int ShareId) {
        db = databaseHelper.getReadableDatabase();
        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)+"'";
        Cursor cursor = db.rawQuery(sql, null);
        if (cursor != null) {
            if (cursor.moveToNext()){
                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.setAddtime(cursor.getString(5));
                shareBean.setUptime(cursor.getString(6));
                shareBean.setBl(cursor.getDouble(7));
            }
        }
        cursor.close();
        db.close();
        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();
        }