我正试图解决从CoreData
提取数据比从Parse中检索数据并将其保存到CoreData
之前执行更早的问题。我如何实现一个队列来执行从Parse提取数据?现在,当我启动应用程序时,数据库已更新,但tableView
中未显示。GCD和核心数据
从CoreData
检索数据:
func fetchFromCoreData() {
do {
let results = try context.executeFetchRequest(fetchRequest)
medicines = results as! [Medicine]
print("FetchFromCoreData")
tableViewMedicines.reloadData()
} catch let error as NSError {
print("Could not fetch \(error), \(error.userInfo)")
}
}
读取数据从parse:
func fetchFromParse() {
let entity = NSEntityDescription.entityForName("Medicine", inManagedObjectContext: context)
let query = PFQuery(className: PFUser.currentUser()!.username!)
query.findObjectsInBackgroundWithBlock { (objects, error) -> Void in
if error == nil {
for object in objects! {
if let name = object["medicineName"] as? String,
amount = object["amountQuantity"] as? String,
time = object["time"] as? String
{
let predicate = NSPredicate(format: "name = %@", name)
self.fetchRequest.predicate = predicate
do{
let fetchedEntities = try self.context.executeFetchRequest(self.fetchRequest) as! [Medicine]
//save to Core Data
if fetchedEntities.count <= 0 {
let medicine = NSManagedObject(entity: entity!, insertIntoManagedObjectContext: self.context)
medicine.setValue(name, forKey: "name")
medicine.setValue(amount, forKey: "amount")
medicine.setValue(time, forKey: "time")
}
} catch let error as NSError{
print(error)
}
}
}
}
do {
try self.context.save()
print("Context.save")
} catch let error as NSError {
print("Could not save \(error), \(error.userInfo)")
}
self.fetchFromCoreData()
}
}
我打电话给他们viewWillAppear
:
override func viewWillAppear(animated: Bool) {
if Reachability.isConnectedToNetwork() {
//fetching data from Parse
fetchFromParse()
fetchFromCoreData()
tableViewMedicines.reloadData()
} else {
//fetching data from Core data
fetchFromCoreData()
logOutButton.enabled = false
}
}
我编辑了我的帖子。我在viewWillAppear中调用它们,但不知道它有什么区别 – kiuzio2
我不知道你会怎么做,但是你可能不得不调用'fetchFromCoreData'方法中的'fetchFromParse'方法,这样你就可以得到首先解析数据。您将测试网络连接,然后从解析中获取数据,否则您只会从磁盘获取数据。 –
这可能是因为你的'findObjectsInBackground'回调将在未来的某个时刻被执行;在你重新加载你的表格数据之后。一个提示是重新考虑你调用tableViewMedicines.reloadData()的位置。 –