Question

我有一个didPressSend函数，它接受在textview中编写的文本，并将其作为String插入到上下文中。一旦插入上下文，NSFetchedResultsController的DidChangeContent会检测到某些内容被插入到上下文中并相应地自动更新集合View（请记住，DidChangeContent绝对是空的）。这是我刚刚为该部分编写的代码。（使用text创建消息是插入上下文的函数）。

 func didPressSendButton(button: UIButton!, withMessageText text: String!, senderId: String! ,senderDisplayName: String!, date: NSDate){

    let context = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext



   createMessageWithText(text, friend: friend!, context: moc, date: date)



    do {
        try context.save()


    } catch let err {
        print(err)
    }


}
private func createMessageWithText(text: String, friend: Friend, context: NSManagedObjectContext, date: NSDate, isSender: Bool = false) -> Mesages {
    let message = NSEntityDescription.insertNewObjectForEntityForName("Mesages", inManagedObjectContext: context) as! Mesages

    message.user = friend
    message.text = text
    message.timestamp = date
    message.isSender = isSender
    friend.lastMessage = message


    return message

}

}

一旦插入上下文，didChangeContent就会检测到它并自动更新集合视图：

lazy var fetchedResultsControler: NSFetchedResultsController = {



    let fetchRequest = NSFetchRequest(entityName: "Mesages")
    fetchRequest.fetchBatchSize = 50
    fetchRequest.sortDescriptors = [NSSortDescriptor(key: "timestamp", ascending: true)]
    fetchRequest.predicate = NSPredicate(format: "user.id = %@", self.friend!.id!)
    let moc = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext
    let frc = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: moc, sectionNameKeyPath: nil, cacheName: nil)
    frc.delegate = self
    return frc
}()



func controllerDidChangeContent(controller: NSFetchedResultsController) {

}

奇怪的是，在DidChangeContent中绝对没有任何东西似乎负责填充collectionView，请记住我用fetchResultsController中的对象数量填充collectionView：

  override func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) ->

    Int {
        if let count = fetchedResultsControler.sections?[0].numberOfObjects {
            return count
        }
        return 0
}

override func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {


    let cell = super.collectionView(collectionView, cellForItemAtIndexPath: indexPath) as! JSQMessagesCollectionViewCell
    return cell
}

override func collectionView(collectionView: JSQMessagesCollectionView!, messageDataForItemAtIndexPath indexPath: NSIndexPath!) -> JSQMessageData! {


    let msg : Mesages = fetchedResultsControler.objectAtIndexPath(indexPath) as! Mesages
    let messageData = JSQMessage(senderId: "" , displayName: "Me", text: msg.text)
    return messageData


}

我还有一个来自firebase的监听器，无论何时向我发送消息，它都会立即检测到它，插入上下文，保存，nsfetchResultsController检测到它，并触发didChangeContent。奇怪的是，它不会在这种情况下自动更新，除非我把collectionView.reloadData放在didChangeContent中，但我不需要为didPressSend放置collectionView.reloadData，因为它自己神奇地自动更新。以与didPressSend相同的方式插入上下文的firebase侦听器的代码如下:(使用text创建消息是插入上下文的函数）。

ref2.observeEventType(.ChildAdded, withBlock: {(snapshot2) in
            let messageId = snapshot2.key
            //first message ID out of 20.
            let messagesRef =     FIRDatabase.database().reference().child("messages").child(messageId)
            messagesRef.observeSingleEventOfType(.Value, withBlock: { (snapshot) in



                let dictionary = snapshot.value as! [NSObject: AnyObject]

                let timestamp = dictionary["timestamp"] as! NSNumber
                let doubleTimestamp = Double(timestamp)

                let date = NSDate(timeIntervalSinceReferenceDate: (doubleTimestamp))








                    self.createMessageWithText(dictionary["text"]! as! String, friend: friend, context: context, date: date, isSender: true)





                do {
                    try context.save()

                }

                catch {
                    print(error)

                }



   private func createMessageWithText(text: String, friend: Friend, context: NSManagedObjectContext, date: NSDate, isSender: Bool = false) -> Mesages {
    let message = NSEntityDescription.insertNewObjectForEntityForName("Mesages", inManagedObjectContext: context) as! Mesages

    message.user = friend
    message.text = text
    message.timestamp = date
    message.isSender = isSender
    friend.lastMessage = message


    return message

}

那就是说，我不确定为什么以及如何使用NSfetchedResultsController填充collectionView。（我真的担心DidPressSend正在填充集合视图，而不会重新加载任何类型的数据）。另外还有一个bug，如果我删除didChangeContent，你可以看到包含NOTHING，didPressSend会停止自动更新。当我添加空的didChangeContent时，集合View开始自动更新（仅适用于didpressSend）。

Answer 1

在委托方法下面实施，并且collectionView或TableView将更新同步。尽快获取新数据。

from functools import reduce
from pyspark.sql.functions import udf
from pyspark.sql.types import IntegerType

# UDF definition
find_diff = udf(lambda a: reduce(lambda x, y: x - y, a), IntegerType()) 

(
    df.
        withColumn(
            'diff',
            find_diff('list')
        ).
        show(truncate=False)
)

+-------+------+----+                                                           
|version|list  |diff|
+-------+------+----+
|v1     |[5, 2]|3   |
|v1     |[2, 5]|-3  |
|v1     |[3, 2]|1   |
|v2     |[2]   |2   |
|v2     |[1, 2]|-1  |
|v2     |[1]   |1   |
+-------+------+----+

NSFetchedResultsController不自动更新集合视图

1 个答案: