NSNumber 的谓词 = 0

Question

我有以下代码从核心数据中获取结果以填充表格视图。

private lazy var fetchedResultsController: NSFetchedResultsController = {
    // Initialize Fetch Request
    let fetchRequest = NSFetchRequest(entityName: "MileageLog")

    // Add Sort Descriptors
    let dateSort = NSSortDescriptor(key: "logDate", ascending: true)
    let mileSort = NSSortDescriptor(key: "mileage", ascending: true)
    fetchRequest.sortDescriptors = [dateSort, mileSort]

    //// Create a new predicate that filters out any object that
    //// have not been exported.
    // let predicate = NSPredicate(format: "wasExported == %@", 0)

    //// Set the predicate on the fetch request
    // fetchRequest.predicate = predicate

    let delegate = UIApplication.sharedApplication().delegate as! AppDelegate
    let managedObjectContext = delegate.managedObjectContext

    // Initialize Fetched Results Controller
    let fetchedResultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: managedObjectContext, sectionNameKeyPath: nil, cacheName: nil)

    fetchedResultsController.delegate = self

    return fetchedResultsController

}()

如果没有谓词，表格视图将填充所有正确排序的记录。取消注释这两行以使谓词生效，根本不会返回任何结果。我的数据集有 4 条记录，wasExported == 1 和 3 条记录，wasExported == 0... wasExported 是一个布尔值，但在核心数据中它存储为 NSNumber .....我做错了什么？

Answer 1

您在谓词中使用了错误的格式说明符。你想要：

let predicate = NSPredicate(format: "wasExported == %d", 0)

%@ 用于对象指针。对于%@，0 被解释为nil 指针。