CKQueryOperation queryCompletionBlock仅运行3次

Question

我正在尝试使用CloudKit和游标从我的iCloud公共数据库下载一批记录。无论resultsLimit如何设置，代码在前3次执行中都工作得很好，但是第四个完成块永远不会执行。如果没有设置resultsLimit，我会得到300条记录；如果设置为50，我会得到150条记录；如果设置为5，我会得到15条记录……

不会报告任何错误，并且该块似乎已添加，但从未执行过。平台是OS X。下面是有问题的代码：

        let queryOp = CKQueryOperation(query: query)
        queryOp.recordFetchedBlock = self.fetchedDetailRecord
        queryOp.resultsLimit = 5
        queryOp.queryCompletionBlock = { [weak self]
          (cursor: CKQueryCursor!, error: NSError!) -> Void in
          println("comp block called with \(cursor) \(error)")
          if error != nil {
            println("Error on fetch \(error.userInfo)")
          } else {
            if cursor != nil {
              let nextOp = CKQueryOperation(cursor: cursor)
              nextOp.recordFetchedBlock = self!.fetchedDetailRecord
              nextOp.queryCompletionBlock = queryOp.queryCompletionBlock
              nextOp.resultsLimit = 5
              self!.publicDatabase?.addOperation(nextOp)
              println("added next fetch")
            } else {
              self!.fileHandle!.closeFile()
              self!.exportProgressIndicator.stopAnimation(self)
            }
          }
        }

        self.publicDatabase?.addOperation(queryOp)

这是来自控制台的结果-

459013587628.012 0 459013587628.621 1 459013587628.863 2 459013587629.113 3 459013587629.339 4通过添加nil调用的comp块459013587828.552 5 459013587828.954 6 459013587829.198 7 459013587829.421 8 459013587829.611 9通过添加nil调用的comp块459013587997.084 10 459013587997.479 11 459013587997.74 12 459013587997.98 13 459013587998.207 14

大数字是调用recordFetchedBlock之间的时间间隔，第二个数字是调用该块的次数。

我是stumped...any关于如何继续下去的想法？容器和publicDatabase是类变量，在运行上面的代码片段之前进行了初始化。

Answer 1

在queryCompletionBlock作用域中定义nextOp的方式在该块的三次迭代后会导致问题。如果您将CKQueryOperation的创建过程分解为它自己的方法，那么问题就不复存在了。

代码如下：

func fetchedDetailRecord(record: CKRecord!) -> Void {
    println("Retrieved record: \(record)")
}

func createQueryOperation(cursor: CKQueryCursor? = nil) -> CKQueryOperation {
    var operation:CKQueryOperation
    if (cursor != nil) {
        operation = CKQueryOperation(cursor: cursor!)
    } else {
        operation = CKQueryOperation(query: CKQuery(...))
    }
    operation.recordFetchedBlock = self.fetchedDetailRecord
    operation.resultsLimit = 5
    operation.queryCompletionBlock = { [weak self]
        (cursor: CKQueryCursor!, error: NSError!) -> Void in
        println("comp block called with \(cursor) \(error)")
        if error != nil {
            println("Error on fetch \(error.userInfo)")
        } else {
            if cursor != nil {
                self!.publicDatabase?.addOperation(self!.createQueryOperation(cursor: cursor))
                println("added next fetch")
            } else {
                self!.fileHandle!.closeFile()
                self!.exportProgressIndicator.stopAnimation(self) 
            }
        }
    }
    return operation
}

func doQuery() {
    println("Querying records...")
    self.publicDatabase?.addOperation(createQueryOperation())
}

Answer 2

这可能是另一种方法(已经更新到Swift 3)。

它不会在第三次迭代后停止，而是会一直持续到最后

var queryOp = CKQueryOperation(query: query)
queryOp.recordFetchedBlock = self.fetchedARecord
queryOp.resultsLimit = 5
queryOp.queryCompletionBlock = { [weak self] (cursor : CKQueryCursor?, error : Error?) -> Void in
    print("comp block called with \(cursor) \(error)")

    if cursor != nil {
        let nextOp = CKQueryOperation(cursor: cursor!)
        nextOp.recordFetchedBlock = self!.fetchedARecord
        nextOp.queryCompletionBlock = queryOp.queryCompletionBlock
        nextOp.resultsLimit = queryOp.resultsLimit

        //this is VERY important
        queryOp = nextOp

        self!.publicDB.add(queryOp)
        print("added next fetch")
    }

}

self.publicDB.add(queryOp)

我成功地使用它从CloudKit检索了成百上千条记录