swift - 如何使用完成处理程序在核心数据swift 5中获取过滤器数据结果

Question

我已经在完成处理程序中创建了 fetch data 方法，并传递了两个参数 search text 和 fetchOfSet 但我没有得到响应。我还必须对记录进行排序并按降序过滤记录。

func fetchAllExpenses(searchText:String, page_no:Int,completionHandler: @escaping (_ responseHandler:[Expense]) -> Void, errorHandler: @escaping (_ error: Error) -> Void) {

    var array = [Expense]()


    // filter the id descending order
    let idDescriptor: NSSortDescriptor = NSSortDescriptor(key: "exp_id", ascending: false)

    // set the fetch limt data
    fetchRequest.fetchLimit = 5

    // sort the data by descending order
    fetchRequest.sortDescriptors = [idDescriptor]

    // need to update every time because can not predicate how many rows before fetched
    fetchRequest.fetchOffset = page_no

    do{
        if let fetchResult = try context.fetch(fetchRequest) as? [Expense]{

            for i in 0..<fetchResult.count {
                let expenses: Expense? = fetchResult[i]
                array.append(expenses!)
                completionHandler(array)
            }

            DispatchQueue.main.async {


            }
        }else{
            print("Not Found More Data")
        }
    } catch let error {
        errorHandler("Error whilve retrieving data..\(error.localizedDescription)" as! Error)
    }
}

Answer 1

首先，核心数据获取是同步的。不需要完成处理程序。

基本上缺少获取请求。而不是返回错误或可选地将错误移交给调用者。如果没有找到记录，则数组为空。searchText并且根本没有使用该参数。

func fetchAllExpenses(pageNo: Int) throws -> [Expense] {

    let fetchRequest : NSFetchRequest<Expense> = Expense.fetchRequest()

    // filter the id descending order
    let idDescriptor = NSSortDescriptor(key: "exp_id", ascending: false)

    // set the fetch limt data
    fetchRequest.fetchLimit = 5

    // sort the data by descending order
    fetchRequest.sortDescriptors = [idDescriptor]

    // need to update every time because can not predicate how many rows before fetched
    fetchRequest.fetchOffset = pageNo

    return try context.fetch(fetchRequest)
}