如何在Core Data中使用带有fetchRequest的谓词

首先摆脱所有NSString和NSDictionary事件.这是斯威夫特!使用Swift本机结构String和Dictionary.

其次,总是把所有好的代码放在do一个do - catch块的范围内.

CoreData谓词具有attribute == value与以下内容非常类似的简单格式aContact.uniqueId! == contactIdentifierString:

var contactIdentifierString = ""

func userSelectedContact(contactIdentifier: String) {

    let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext

    do {
        let fetchRequest : NSFetchRequest = Contact.fetchRequest()
        fetchRequest.predicate = NSPredicate(format: "uniqueId == %@", contactIdentifier)
        let fetchedResults = try context.fetch(fetchRequest) as! [Contact]
        if let aContact = fetchedResults.first {
           providerName.text = aContact.providerName
        }
    }
    catch {
        print ("fetch task failed", error)
    }

}

代码假定有一个NSManagedObject子类Contact包含

@nonobjc public class func fetchRequest() -> NSFetchRequest {
    return NSFetchRequest(entityName: "Contact")
}