Question

我正在使用FRC，我想创建根据日期（DD MMMM）对数据进行分组的部分！每个任务都有一个日期，我正在使用该日期并将其格式化为节标题。

我正在使用他们在Objective C中提供的Apple示例代码，并将其转换为swift。这是代码：

import UIKit
import CoreData

class completedNotes: NSManagedObject
{
    @NSManaged var cNote: String
    @NSManaged var cPriorityColor: UIColor
    @NSManaged var cDate: Date

}


extension completedNotes {
var sectionIdentifier : String? {
    // Create and cache the section identifier on demand.

    self.willAccessValue(forKey: "sectionIdentifier")
    var tmp = self.primitiveValue(forKey: "sectionIdentifier") as? String
    self.didAccessValue(forKey: "sectionIdentifier")

    if tmp == nil {
        if let timeStamp = self.value(forKey: "cDate") as? NSDate {
            /*
             Sections are organized by month and year. Create the section
             identifier as a string representing the number (year * 1000) + month;
             this way they will be correctly ordered chronologically regardless
             of the actual name of the month.
             */
            let calendar  = NSCalendar.current

            let components = calendar.dateComponents([.year, .month,], from: timeStamp as Date)
            tmp = String(format: "%ld", components.year! * 1000 + components.month!)
            self.setPrimitiveValue(tmp, forKey: "sectionIdentifier")
        }
    }
    return tmp
}
}

上面的代码在NSManagedObject中，我正在创建一个瞬态属性sectionIdentifier。它取值为NSDagedObject的cDate值。

然后在titlesforheaderinSection

 func tableView(_ tableView: UITableView, titleForHeaderInSection section: Int) -> String? {
    struct Formatter {
        static let formatter : DateFormatter = {
            let fmt = DateFormatter()
            let dateFormat = DateFormatter.dateFormat(fromTemplate: "MMMM yyyy", options: 0,
                                                      locale: NSLocale.current)
            fmt.dateFormat = dateFormat
            return fmt
        }()
    }

    if let theSection = fetchedResultsController1.sections?[section] as? NSFetchedResultsSectionInfo,
        let numericSection = Int(theSection.name) {
        var components = DateComponents()
        components.year = numericSection / 1000
        components.month = numericSection % 1000
        if let date = Calendar.current.date(from: components) {
            let titleString = Formatter.formatter.string(from: date)
            return titleString
        }
    }
    return nil

}

这是我用于其他tableview函数的代码：

func numberOfSections(in tableView: UITableView) -> Int {
    return (fetchedResultsController1.sections?.count)!
}

func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return fetchedResultsController1.sections![section].numberOfObjects
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCell(withIdentifier: cellid, for: indexPath) as! TasksTableViewCell
    cell.selectionStyle = .none

    cell.textview.text = fetchedResultsController1.object(at: indexPath).cNote
    cell.priorityline.backgroundColor = fetchedResultsController1.object(at: indexPath).cPriorityColor

    return cell
}

这是NSFetchedResultsController：

let aFetchedResultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: self.moContext1, sectionNameKeyPath: "sectionIdentifier", cacheName: nil)
    aFetchedResultsController.delegate = self
    _fetchedResultsController = aFetchedResultsController as? NSFetchedResultsController<completedNotes>

为什么我无法在tableview中显示任何部分以及为什么当我删除最后一个tableview单元格时，应用程序崩溃？

谢谢！

Answer 1

传递给String result = output.contains("1") ? output.substring(output.indexOf("1")) : "0";的关键路径获取结果控制器的参数必须是可见的 Objective-C运行时。在Swift 4中需要显式注释使用sectionNameKeyPath:（也比较How can I deal with @objc inference deprecation with #selector() in Swift 4?）：

@objc

如果没有，则会自动忽略部分名称密钥路径。

如何在Swift 4中使用FetchedResultsController获取DateSectionTitles

1 个答案: