recycle的切换list和grid，数据库的一些操作

if (flag==true){
rv.setLayoutManager(new GridLayoutManager(Main2Activity.this,2));
setaba();
}else{
rv.setLayoutManager(new LinearLayoutManager(Main2Activity.this,LinearLayoutManager.VERTICAL,false));
setaba();
}

//数据库

public class Dao {private Dbhelpher myHelper;private SQLiteDatabase db;//实现一个方法传递一个布局public Dao(Context context) {myHelper = new Dbhelpher(context);}//添加历史记录public int   add(String json){db = myHelper.getWritableDatabase();db.execSQL("insert into jilu values(null,?)",new String[]{json});//成功返回1return 1;}//查询数据库public List<String> sel(){List<String> list=new ArrayList<>();db = myHelper.getWritableDatabase();Cursor cursor = db.rawQuery("select * from jilu", null);while (cursor.moveToNext()){//String id = cursor.getString(cursor.getColumnIndex("id"));String json = cursor.getString(cursor.getColumnIndex("json"));list.add(json);}return list;}//清空历史记录public void del(){db = myHelper.getWritableDatabase();db.execSQL("delete from jilu");}}