ios - 如何使用 CloudKit 通过 CKQueryOperation 迭代查询直到游标为零？

Question

我将如何声明一个从 CloudKit 中检索记录的闭包，该闭包会迭代调用自身直到获取所有记录？下面的代码就是这样做的，除了我收到一条错误消息

Variable used within its own initial value

在我将闭包 queryCompletionBlock 分配给属性的行中，该属性在闭包本身的声明中使用与查询操作相同的名称。基本上，我得到一个错误，因为我在声明闭包之前在闭包声明中调用了闭包本身。

    let predicate = NSPredicate(value: true)
    let query = CKQuery(recordType: DatabaseNameStrings.recordTypeEntry, predicate: predicate)
    let queryOperation = CKQueryOperation(query: query)
    queryOperation.desiredKeys = [DatabaseNameStrings.fieldNameCreatedAt, DatabaseNameStrings.fieldNameText]
    let queryCompletionBlock = {
        (cursor: CKQueryOperation.Cursor?, error: Error?) in
        if let error = error {
            print(error.localizedDescription)
        } else if let cursor = cursor {
            let queryOperation = CKQueryOperation(cursor: cursor)
            queryOperation.desiredKeys = [DatabaseNameStrings.fieldNameCreatedAt, DatabaseNameStrings.fieldNameText]
            queryOperation.queryCompletionBlock = queryCompletionBlock // Error message "Variable used within its own initial value"
            queryOperationQueue.addOperation(queryOperation)
        }
    }
    queryOperation.queryCompletionBlock = queryCompletionBlock
    queryOperationQueue.addOperation(queryOperation)

Answer 1

一个可行的选项是引用原始查询操作的 queryCompletionBlock。

let predicate = NSPredicate(value: true)
let query = CKQuery(recordType: DatabaseNameStrings.recordTypeEntry, predicate: predicate)
let queryOperation = CKQueryOperation(query: query)
queryOperation.desiredKeys = [DatabaseNameStrings.fieldNameCreatedAt, DatabaseNameStrings.fieldNameText]
let queryCompletionBlock = {
    (cursor: CKQueryOperation.Cursor?, error: Error?) in
    if let error = error {
        print(error.localizedDescription)
    } else if let cursor = cursor {
        let newOperation = CKQueryOperation(cursor: cursor)
        newOperation.desiredKeys = queryOperation.desiredKeys
        newOperation.queryCompletionBlock = queryOperation.queryCompletionBlock
        newOperationQueue.addOperation(newOperation)
    }
}
queryOperation.queryCompletionBlock = queryCompletionBlock
queryOperationQueue.addOperation(queryOperation)