CloudKit查询中的UITableView部分

Question

我有一个简单的CloudKit记录,它有两个字段,名称和等级.我希望能够对CloudKit进行查询,返回所有记录,但按等级分组.我知道我可以使用NSFetchResultsController执行此操作,但似乎无法使用CKQuery找到一种简单的方法.

获取的当前代码:

    func fetchTeachers(_ completion: @escaping (_ teachers: [CKRecord]?, _ error: NSError?) -> () ) {

    let query = CKQuery(recordType: TeacherType, predicate: NSPredicate(value: true))
    query.sortDescriptors = [NSSortDescriptor(key:"Grade",ascending:true)]

    publicDB.perform(query, inZoneWith: nil) { results, error in
        completion(results, error as NSError?)
    }
}

Answer 1

要将检索到的 CKRecords 数组拆分为多个部分以在 UITableView 中显示，您可以使用下面的帮助器类。

（CKQuery 本身不提供执行此分段的能力 - 它只是使您能够检索记录数组，可选择排序。）

使用SectionedCKRecords类：

首先，使用 CKQuery 从 CloudKit 获取所需的记录。（您的示例代码已经这样做了。）这将为您提供一个 CKRecords 数组。

假设这些记录（根据您的示例代码）包含一个存储字符串值的“ Grade ”键，并且您希望根据“ Grade ”将记录拆分为多个部分。

简单地：

1.）初始化SectionedCKRecords与CKRecords的阵列，且所期望的sectionNameKey：

let sectionedRecords = SectionedCKRecords(records: records, sectionNameKey: "Grade")

2.) 实现您的UITableViewDataSource以在sectionedRecords上调用适当的方法：

SectionedCKRecords暴露出类似的方法NSFetchedResultsController。

class YourDataSource: UITableViewDataSource {

    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let record = sectionedRecords.record(at: indexPath)
        // TODO: construct a UITableViewCell based on the record
        // ...
    }

    func numberOfSections(in tableView: UITableView) -> Int {
        return sectionedRecords.sections.count
    }

    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return sectionedRecords.sections[section].numberOfRecords
    }

    func sectionIndexTitles(for tableView: UITableView) -> [String]? {
        return sectionedRecords.sectionIndexTitles
    }

    // etc...

}

自定义sectionIndexTitle行为：

如果您想自定义 sectionIndexTitles 的生成方式，您可以将sectionIndexTitleForSectionName闭包传递给SectionedCKRecords初始值设定项。

默认情况下，SectionedCKRecords的行为相匹配NSFetchedResultsController用于发电sectionIndexTitles，使用一节名字的大写首字母。

闭包接受一个字符串（sectionName）作为输入，并返回 sectionIndexTitle。

SectionIndexTitleForSectionName结构中提供了一些示例闭包。

例子：

let sectionedRecords = SectionedCKRecords(records: records, sectionNameKey: "Grade", sectionIndexTitleForSectionName: SectionIndexTitleForSectionName.firstLetterOfString)

SectionedCKRecords.swift: (Swift 3)

// SectionedCKRecords.swift (Swift 3)
// © 2016 @breakingobstacles (http://stackoverflow.com/users/57856/breakingobstacles)
// Source: http://stackoverflow.com/a/39737583/57856
//
// License: The MIT License (https://opensource.org/licenses/MIT)
//    Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
//    The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
//    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//

import UIKit
import CloudKit

// MARK: - SectionedCKRecords
class SectionedCKRecords {

    private let sectionNameToSection: [String: Int]
    private let sectionIndex: [String]
    private let sectionIndexTitleToFirstSection: [String: Int]

    init(records: [CKRecord], sectionNameKey: String, sectionIndexTitleForSectionName: (String) -> String? = SectionIndexTitleForSectionName.firstLetterOfString) {

        self.records = records
        self.sectionNameKey = sectionNameKey

        // split records into sections
        let splitResults = split(records: records, bySectionNameKey: sectionNameKey)
        self.sections = splitResults.sections
        self.sectionNameToSection = splitResults.sectionNameToSection

        // build section index
        var sectionIndex: [String] = []
        var sectionIndexTitleToFirstSection: [String: Int] = [:]
        for (index, section) in splitResults.sections.enumerated() {
            guard let sectionIndexTitle = sectionIndexTitleForSectionName(section.name) else {
                continue
            }
            section.indexTitle = sectionIndexTitle
            if sectionIndexTitleToFirstSection.index(forKey: sectionIndexTitle) == nil {
                sectionIndex.append(sectionIndexTitle)
                sectionIndexTitleToFirstSection[sectionIndexTitle] = index
            }
        }

        self.sectionIndex = sectionIndex
        self.sectionIndexTitleToFirstSection = sectionIndexTitleToFirstSection
    }

    /// MARK: - Configuring Information

    // The input array of records.
    let records: [CKRecord]

    // The key on the CKRecords used to determine the section they belong to. Assumes that record[sectionNameKey] returns a String value.
    let sectionNameKey: String

    /// MARK: - Accessing Results

    // Returns the record at the given index path in the sectioned records.
    func record(at indexPath: IndexPath) -> CKRecord {
        return sections[indexPath.section].records[indexPath.row]
    }

    /// MARK: - Querying Section Information

    // The sections for the fetch results.
    private(set) var sections: [SectionInfo]

    // Returns the section number for a given section title and index in the section index.
    func section(forSectionIndexTitle sectionIndexTitle: String, at: Int) -> Int {
        return sectionIndexTitleToFirstSection[sectionIndexTitle] ?? -1
    }

    // The array of section index titles.
    var sectionIndexTitles: [String] {
        get {
            return sectionIndex
        }
    }
}

class SectionInfo: CustomStringConvertible {
    var numberOfRecords: Int { return records.count }
    let name: String
    fileprivate(set) var indexTitle: String?
    private(set) var records: [CKRecord]

    init(name: String, indexTitle: String? = nil, records: [CKRecord] = []) {
        self.name = name
        self.indexTitle = indexTitle
        self.records = records
    }

    fileprivate func add(record: CKRecord) {
        records.append(record)
    }

    // MARK: - CustomStringConvertible
    var description: String {
        return "SectionInfo(name: \"\(name)\", indexTitle: \(indexTitle), numberOfRecords: \(numberOfRecords), records: \(records))"
    }
}

// Example options for mapping section names to section index titles:
struct SectionIndexTitleForSectionName {
    static let firstLetterOfString = { (string: String) -> String? in
        guard let firstCharacter = (string as String).characters.first else {
            return ""
        }
        return String(firstCharacter).uppercased()
    }
    static let fullString = { (string: String) -> String? in
        return string as String
    }
    static let fullStringUppercased = { (string: String) -> String? in
        return (string as String).uppercased()
    }
}

/// split(records:bySectionNameKey)
///
/// Takes an input array of CKRecords, and splits them into sections using the (String) value retrieved from each record's "sectionNameKey".
///
/// The relative ordering of the records in the input array is maintained in each section.
///
/// - parameter records:                         An array of records to be split into sections.
/// - parameter bySectionNameKey:                The key on the CKRecords used to determine the section they belong to.
///                                              Assumes that record[sectionNameKey] returns a String value.
///
/// - returns: An array of sections, and a dictionary mapping sectionName -> the index in the sections array.
func split(records: [CKRecord], bySectionNameKey sectionNameKey: String) -> (sections: [SectionInfo], sectionNameToSection: [String: Int])
{
    func sectionName(forRecord record: CKRecord, withSectionNameKey sectionNameKey: String) -> String? {
        guard let sectionNameValue = record.object(forKey: sectionNameKey) else {
            assertionFailure("Record is missing expected sectionNameKey (\(sectionNameKey)): \(record)")
            return nil
        }
        guard let sectionName = sectionNameValue as? String else {
            assertionFailure("Record[\(sectionNameKey)] contains a value that cannot be converted directly to String. Record: \(record)")
            return nil
        }
        return sectionName
    }

    var sections: [SectionInfo] = []
    var sectionNameToSection: [String: Int] = [:]

    var currentSection: SectionInfo? = nil
    for record in records {
        guard let sectionName = sectionName(forRecord: record, withSectionNameKey: sectionNameKey) else {
            assertionFailure("Unable to obtain expected sectionNameKey (\(sectionNameKey)) for record: \(record)")
            continue
        }

        if let currentSection = currentSection, currentSection.name == sectionName {
            currentSection.add(record: record)
        }
        else {
            // find existing section, if present
            if let desiredSectionIndex = sectionNameToSection[sectionName] {
                sections[desiredSectionIndex].add(record: record)
            }
            else {
                // create new section
                let newSection = SectionInfo(name: sectionName, records: [record])
                sections.append(newSection)
                sectionNameToSection[sectionName] = sections.count - 1
                currentSection = newSection
            }
        }
    }

    return (sections: sections, sectionNameToSection: sectionNameToSection)
}