Question

我有一个视图控制器，可以显示Core Data中项目的详细信息。要查找的特定项目将从前一个控制器传递给控制器。

以下是基本代码：

class ItemDetailViewController: UIViewController, UITableViewDelegate, UITableViewDataSource{

@IBOutlet weak var itemLabel: UILabel!

var selectedItemObjectID:String!

        override func viewDidAppear(animated: Bool) {

                //Fetch the the list of items from the context
                var appDel:AppDelegate = (UIApplication.sharedApplication().delegate as! AppDelegate)
                var request = NSFetchRequest(entityName: "Item")
                var context:NSManagedObjectContext = appDel.managedObjectContext!
                var error: NSError?
                var results:NSArray = context.executeFetchRequest(request, error: &error)!

                //optional, avoids potential compiler error
                request.returnsObjectsAsFaults = false

                if (results.count > 0) {
                    for fetchResult in results {
                        println("POPULATING THE DETAILS PAGE...")
                        println("fetchResult.objectID is \(fetchResult.objectID)")
                        println("selectedItemObjectID is \(selectedItemObjectID)")
                        //If the array entry matches the data passed to us, then populate the item details screen
                        if (fetchResult.objectID  == selectedItemObjectID) { 
                            itemLabel.text = fetchResult.valueForKey("itemName") as? String         
                } else {
                    println("No items in the database...")
                }
            }

我遇到的问题是，在我看来，我相互比较的objectID看起来完全一样。然而，if语句未被触发，并且itemLabel.text永远不会被更改。当for循环遍历应该匹配的那个时，这是输出：

POPULATING THE DETAILS PAGE...
fetchResult.objectID is 0xd000000000080000 <x-coredata://5F0AE77F-A83A-41BC-9361-0DE37F120776/Item/p2>
selectedItemObjectID is 0xd000000000080000 <x-coredata://5F0AE77F-A83A-41BC-9361-0DE37F120776/Item/p2>

它们看起来完全一样！我的if语句是否形成错误？我是否会以错误的方式使用objectID？

Answer 1

我明白了。在if比较中，我需要使用fetchresult.fetchResult.objectID.description而不是fetchresult.fetchResult.objectID。

请参阅下面的更正代码：

class ItemDetailViewController: UIViewController, UITableViewDelegate, UITableViewDataSource{

@IBOutlet weak var itemLabel: UILabel!

var selectedItemObjectID:String!

        override func viewDidAppear(animated: Bool) {

                //Fetch the the list of items from the context
                var appDel:AppDelegate = (UIApplication.sharedApplication().delegate as! AppDelegate)
                var request = NSFetchRequest(entityName: "Item")
                var context:NSManagedObjectContext = appDel.managedObjectContext!
                var error: NSError?
                var results:NSArray = context.executeFetchRequest(request, error: &error)!

                //optional, avoids potential compiler error
                request.returnsObjectsAsFaults = false

                if (results.count > 0) {
                    for fetchResult in results {
                        println("POPULATING THE DETAILS PAGE...")
                        println("fetchResult.objectID is \(fetchResult.objectID)")
                        println("selectedItemObjectID is \(selectedItemObjectID)")
                        //If the array entry matches the data passed to us, then populate the item details screen
                        if (fetchResult.objectID.description  == selectedItemObjectID) { 
                            itemLabel.text = fetchResult.valueForKey("itemName") as? String         
                } else {
                    println("No items in the database...")
                }
            }

如何将fetched ObjectID与字符串进行比较？

1 个答案: