android alert

AlertDialog.Builder dlg = new AlertDialog.Builder(this);
        dlg.setTitle("警告");
        dlg.setMessage("确定要删除数据库内容吗，一旦删除数据将不能恢复！！！");
        dlg.setNegativeButton("取消",null);
        dlg.setPositiveButton("确定",new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialogInterface, int i) {
                if(sqliteOpenHelper==null)
                {
                    return;
                }
                sqliteOpenHelper.deleteall();
                m_showlog.setText("数据清除完成");
            }
        });
        dlg.create();
        dlg.show();