我应该为这个可选添加啥标识符？

Posted 2023-03-05

【中文标题】我应该为这个可选添加啥标识符？

【英文标题】：What identifier should I add for this optional?我应该为这个可选添加什么标识符？

【发布时间】：2016-04-28 06:54:02

【问题描述】：

我想添加这个可选的

var mapRegion : MKCoordinateRegion

它给了我一个错误，我需要在类旁边有一个标识符：

class TableViewController: UITableViewController, NSFetchedResultsControllerDelegate,

那个标识符是什么？

文件如下所示：

import UIKit
import CoreData
import MapKit

class TableViewController: UITableViewController, NSFetchedResultsControllerDelegate,  

let moc = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext
var frc : NSFetchedResultsController = NSFetchedResultsController()

var mapRegion : MKCoordinateRegion


func fetchRequest() -> NSFetchRequest 

    let fetchRequest = NSFetchRequest(entityName: "Item")
    let sortDescriptor = NSSortDescriptor(key: "name",
                                          ascending: true)
    fetchRequest.sortDescriptors = [sortDescriptor]
    return fetchRequest

func getFRC() -> NSFetchedResultsController 

    frc = NSFetchedResultsController(fetchRequest: fetchRequest(), managedObjectContext: moc, sectionNameKeyPath: nil, cacheName: nil)
    return frc


override func viewDidLoad() 
    super.viewDidLoad()

    frc = getFRC()
    frc.delegate = self

    do 
        try frc.performFetch()
     catch 
        print("Failed to perform initial fetch.")
        return
    

    self.tableView.rowHeight = 480
    self.tableView.backgroundView = UIImageView( image: UIImage(named: "flatgrey2"))
    self .tableView.reloadData()


override func viewDidAppear(animated: Bool) 
    frc = getFRC()
    frc.delegate = self

    do 
        try frc.performFetch()
     catch 
        print("Failed to perform initial fetch.")
        return
    
    self .tableView.reloadData()



override func didReceiveMemoryWarning() 
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.


// MARK: - Table view data source


override func numberOfSectionsInTableView(tableView: UITableView) -> Int 
    // #warning Incomplete implementation, return the number of sections
    let numberOfSections = frc.sections?.count
    return numberOfSections!



override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int 
    // #warning Incomplete implementation, return the number of rows
    let numberofRowsInSection = frc.sections?[section].numberOfObjects

    return numberofRowsInSection!

    //return 0





override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell 
    let cell = tableView.dequeueReusableCellWithIdentifier("cell", forIndexPath: indexPath)

    if indexPath.row % 2 == 0 
        cell.backgroundColor = UIColor.clearColor()
     else 
        cell.backgroundColor = UIColor.whiteColor().colorWithAlphaComponent(0.2)
        cell.textLabel?.backgroundColor = UIColor.whiteColor().colorWithAlphaComponent(0.0)
        cell.detailTextLabel?.backgroundColor = UIColor.whiteColor().colorWithAlphaComponent(0.0)
    


    // Configure the cell...
    cell.textLabel?.textColor = UIColor.darkGrayColor()
    cell.detailTextLabel?.textColor = UIColor.darkGrayColor()

    let item = frc.objectAtIndexPath(indexPath) as! Item
    cell.textLabel?.text = item.name
    cell.imageView?.image = UIImage(data: (item.image)!)

    return cell






/*
// Override to support conditional editing of the table view.
override func tableView(tableView: UITableView, canEditRowAtIndexPath indexPath: NSIndexPath) -> Bool 
    // Return false if you do not want the specified item to be editable.
    return true

*/


// Override to support editing the table view.

override func tableView(tableView: UITableView, commitEditingStyle editingStyle: UITableViewCellEditingStyle, forRowAtIndexPath indexPath: NSIndexPath) 

    let managedObject : NSManagedObject = frc.objectAtIndexPath(indexPath) as! NSManagedObject
    moc.deleteObject(managedObject)

    do 
        try moc.save()
     catch 
        print ("Failed to save.")
        return
    


func controller(controller: NSFetchedResultsController, didChangeObject anObject: AnyObject, atIndexPath indexPath: NSIndexPath?, forChangeType type: NSFetchedResultsChangeType, newIndexPath: NSIndexPath?) 
    tableView.reloadData()







/*
// Override to support rearranging the table view.
override func tableView(tableView: UITableView, moveRowAtIndexPath fromIndexPath: NSIndexPath, toIndexPath: NSIndexPath) 


*/

/*
// Override to support conditional rearranging of the table view.
override func tableView(tableView: UITableView, canMoveRowAtIndexPath indexPath: NSIndexPath) -> Bool 
    // Return false if you do not want the item to be re-orderable.
    return true

*/


// MARK: - Navigation

// In a storyboard-based application, you will often want to do a little preparation before navigation
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) 
    // Get the new view controller using segue.destinationViewController.
    // Pass the selected object to the new view controller.
    if segue.identifier == "edit" 

        let cell = sender as! UITableViewCell
        let indexPath = tableView.indexPathForCell(cell)
        let itemController : AddEditVC = segue.destinationViewController as! AddEditVC
        let item : Item = frc.objectAtIndexPath(indexPath!)  as! Item
        itemController.item = item
    

【参考方案1】：

变量在声明时应该有一个值，否则会显示此错误。为变量var mapRegion : MKCoordinateRegion 赋值。如果该值是在稍后阶段给出的，即，如果它取决于任何计算，则将其设置为像这样的可选 var mapRegion : MKCoordinateRegion? 但是，只要您想使用 ma​​pRegion 值，就必须通过放置变量名末尾的感叹号。

【参考方案2】：

您已声明var mapRegion : MKCoordinateRegion，但没有任何初始化程序或默认值。要使其成为可选项，只需添加 ? 即可，因此声明：

var mapRegion : MKCoordinateRegion?