January 2020
Intermediate to advanced
356 pages
6h 4m
Chinese
Content preview from Swift游戏开发经典实例
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存储数据
｜
173
// 'record'
是一个
CKRecord
对象
//
读取一个字符值，如果是空值则转换为空字符串
let message = record.object(forKey: "contents") as? String ?? ""
//
读取一个
Date
类型，如果是空值则转换为当前日期
let date = record.object(forKey: "modifiedAt") as? Date ?? Date()
讨论
在查询数据库时，还可以指定排序。首先必须在排序字段上添加索引，步骤是一样
的，但
Index Type
修改为
Sortable
。然后，可以创建一个
SortDescriptor
，将它传
给
CKQuery
：
//
按修改日期排序
let sortDescriptor = NSSortDescriptor(key: "modificationDate",
ascending: false)
query.sortDescriptors = [sortDescriptor]
接收结果集的闭包可以在任何
Operation
队列运行，如果你需要更新
UI
，请让它在
主队列中运行。具体请参考
1.13
节。
5.13
从
CloudKit
数据库中删除记录
问题
你想从
CloudKit
数据库中删除一条记录。
解决方案
要删除记录，必须知道记录的
ID
。一种方法是先用查询获得你想删除的记录（参
考
5.12
节）。
一旦你获得记录
ID
，就可以调用
delete
方法，并传入要删除的记录 ...
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I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.