假设用户在select PHYSICIAN.PHYSICIAN_ID, PHYSICIAN.firstname_physician, PHYSICIAN.lastname_physician, phone.phone_number, count(patient.patient_id) as "Numbers of new patients he/she can take"
from patient, physician, physician_phone, phone
where physician.physician_id = patient.physician_id and PHYSICIAN_PHONE.PHYSICIAN_ID = PHYSICIAN.PHYSICIAN_ID and phone.PHONE_ID = physician_phone.PHONE_ID
group by PHYSICIAN.PHYSICIAN_ID, PHYSICIAN.firstname_physician, PHYSICIAN.lastname_physician, physician_phone.phone_id, phone.phone_number
having count(patient.patient_id) = 0;
流中启动异步请求，然后将其关闭。如果他们迅速带回PageViewController，它将不会导航到正确的页面，因为正在进行一个异步请求（该请求确定要显示的下一个逻辑页面）。防止用户解雇控制器或要求他们不要的标准吗？如果不是，我该如何管理后台任务，因此我知道保持加载屏幕状态并等待浏览页面，直到最后一个请求完成并更改状态/服务器端数据？