CloudKit查询中的UITableView部分

Question

I have a simple CloudKit record that has two fields, Name and Grade. I would like to be able to do a query to CloudKit returning all of the records but grouped into sections by Grade. I know I can do this with NSFetchResultsController but can't seem to find an easy way to do this with CKQuery.

Current code for fetching:

    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

To split an array of retrieved CKRecords into sections for display in a UITableView, you can use the helper class below.

(A CKQuery itself does not provide the ability to do this sectioning - it just enables you to retrieve an array of records, optionally sorted.)

---

Using the SectionedCKRecords class:

First, fetch the desired records from CloudKit using a CKQuery. (Your example code already does this.) This will provide you with an array of CKRecords.

Let's assume that those records (per your example code) contain a " Grade " key that stores a String value, and that you want to split the records into sections based on the " Grade ".

Simply:

1.) Initialize a SectionedCKRecords with the array of CKRecords, and the desired sectionNameKey :

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

2.) Implement your UITableViewDataSource to call the appropriate methods on sectionedRecords :

SectionedCKRecords exposes methods similar to those of 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...

}

Customizing sectionIndexTitle Behavior:

If you'd like to customize how the sectionIndexTitles are generated, you can pass a sectionIndexTitleForSectionName closure to the SectionedCKRecords initializer.

By default, SectionedCKRecords matches the behavior of NSFetchedResultsController for generating sectionIndexTitles , using the capitalized first letter of the section name.

The closure takes a String (the sectionName) as input, and returns the sectionIndexTitle.

Some example closures are provided in the SectionIndexTitleForSectionName struct.

Example:

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)
}

Answer 2

Just as a model you could write something resembling this for a tableView. You can edit your dashboard entries or keys to sort by whatever you want.

Teachers.swift

class Teachers: NSObject {
var recordID: CKRecordID!
var name: String!
var grade: String!
}

You might have a submit class like this.

SubmitViewController.swift

//There can be a fail at any time so CloudKit send methods have an
//error being passed into the closure. You can set an isDirty property.
CKContainer.default().publicCloudDatabase.save(teacherRecord) { [unowned self] record, error in
DispatchQueue.main.async {
//code 
ViewController.dirty = true
//code }

ViewController.swift

//Property that will store an array of Teachers
//objects so that you can show them in a table view
var teachers = [Teachers]() 

//A “dirty” flag tracks when the derived data is out of sync with the primary data.
//It is set when the primary data changes. If the flag is set when the derived data
//is needed, then it is reprocessed and the flag is cleared. Otherwise,
//the previous cached derived data is used.
static var isDirty = true

//viewWillAppear() is going to clear the table view's selection if it has one,
//then it will use the isDirty flag to call loadTeachers() if it's needed.
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)

if let indexPath = tableView.indexPathForSelectedRow {
    tableView.deselectRow(at: indexPath, animated: true)
}

if ViewController.dirty {
    loadTeachers()
}
} 

func loadTeachers() {
let pred = NSPredicate(value: true)
let sort = NSSortDescriptor(key: "creationDate", ascending: true)
let query = CKQuery(recordType: "TeacherType", predicate: pred)
query.sortDescriptors = [sort]

let operation = CKQueryOperation(query: query)

//Set the desiredKeys property to be an array of the record keys you want
operation.desiredKeys = ["name", "grade"]
operation.resultsLimit = 25

//CKQueryOperation has two closures. One streams records and one is
//called when the records have been downloaded. To handle this you
//can create a new array that will hold the teachers as they are parsed.
var newTeachers = [Teachers]()

//Set a recordFetchedBlock closure on the CKQueryOperation object.
//This will be given a CKRecord value for every record that gets
//downloaded, and the convert that into a Teachers object. 
operation.recordFetchedBlock = { record in
let teacher = Teachers()
teacher.recordID = record.recordID
teacher.name = record["name"] as! String
teacher.grade = record["grade"] as! String
newTeachers.append(teacher)
}

//Called by CloudKit when all records have been downloaded, and will be
//given two parameters: a query cursor and an error if there was one.
//The query cursor is useful if you want to implement paging.
operation.queryCompletionBlock = { [unowned self] (cursor, error) in
DispatchQueue.main.async {
    if error == nil {
        self.teachers = newTeachers
        self.tableView.reloadData()
    } else {
        let ac = UIAlertController(title: "Fetch failed", message: "Please try again: \(error!.localizedDescription)", preferredStyle: .alert)
        ac.addAction(UIAlertAction(title: "OK", style: .default))
        self.present(ac, animated: true)
    }
}
}

//Ask CloudKit to run it
CKContainer.default().publicCloudDatabase.add(operation)

} //End of loadTeachers()

Confirm:

• Did you see your data in the CloudKit Dashboard?
• Did you name your record type "TeacherType" when writing and reading?
• For the Metadata Indexes, did you select Query next to ID, and Sort next to Date Created?
• Is your device online?

*With help from Paul.