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我将如何声明一个从 CloudKit 检索记录的闭包，该闭包迭代地调用自身，直到获取所有记录？下面的代码可以做到这一点，除了我得到一个错误说

在自己的初始值内使用的变量

在我将闭包 queryCompletionBlock 分配给闭包本身声明中查询操作的相同名称的属性的那一行。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)
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1 回答 1

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一个应该起作用的选项是引用queryCompletionBlock原始查询操作的。

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)
于 2018-12-07T04:38:57.977 回答