搜索iCloud文件Searching for iCloud Documents

文件有一个设备上的一个应用创建，通过相同的应用运行在用户的其他设备上。一个应用发现文档在一个iCloud容器目录，是通过使用一个元数据查询对象，这是一个NSMetadatQuery对象的实例。一个元数据查询对象为文件查找可用的iCloud容器目录。Documents created by an app on one device must be discoverable by the same app running on the user’s other devices. An app discovers documents in an iCloud container directory is by using a metadata query object, which is an instance of the NSMetadataQuery class. A metadata query object searches the available iCloud container directories for files matching the criteria you specify.

因为文件会在任意时间出现在一个容器目录中（或者从目录中消失），它经常会使场景开启一个队列，并让它运行。在这种情况下，你应该在你应用的一些主要部分创建查询对象，并在你应用的声明周期与该对象保持一个关联。Because documents can appear in a container directory (or disappear from the directory) at any time, it often makes sense to start a query and leave it running. In such a case, you should create the query object in some central part of your app and keep a reference to that object for the lifetime of your app.

开始你的文档的寻找Starting Your Search for Documents

STEMasterViewController类在你应用声明的开始创建一个元数据查询对象，并打开它。这个查询会立刻返回一个文档的初始设置，当发生改变时发送修改。The STEMasterViewController class creates a metadata query object early in the life of the app and starts it. This query returns an initial set of documents right away and sends later updates when changes occur.

因为查询在应用运行过程中不断运行，STEMasterViewController类持续地使用一个实例变量来存储一个查询对象。Because the query runs constantly while the app is running, the STEMasterViewController class uses an instance variable to store a query object persistently.

你在应用启动循环期间初始化_query实例变量。You initialize the _query instance variable during the app launch cycle.

查询结果的过程Processing the Search Results

搜索结果在两个阶段传递：初始的收集阶段和修改阶段。初始阶段在你打开一个元数据查询就会立刻发生并且是第一组结果返回。之后，查询对象发送修改通知只在目录中的文件改变时。对于两个阶段，元数据查询结果包括所有在特定位置找到的文件。Search results are delivered in two phases: the initial gathering phase and the update phase. The initial gathering phase occurs immediately after you start a metadata query and is the first set of results to be returned. Thereafter, the query object sends update notifications only when the files in the directory change. For both the initial gathering phase and for updates, the metadata query results include all of the files currently found in the specified location.

简单文件编辑应用那个中，使用元数据查询通知来修改它的文档列表，刷新它的用户接口。The Simple Text Editor app uses the metadata query notifications to update its list of documents and refresh its user interface accordingly.

创建并运行你的应用Building and Running Your App

在这一点上，你应该有所有你需要构建并运行完整的应用程序。你应该能够在iCloud创建新文档，打开现有文档，编辑这些文档的内容。如果您有多个相关设备配置概要文件，你应该也可以插入每个设备，看到文件上创建一个出现在另一个。At this point, you should have everything you need to build and run the complete app. You should be able to create new documents in iCloud, open existing documents, and edit the contents of those documents. If you have multiple devices associated with the provisioning profile, you should also be able to plug in each device and see the files created on one show up on the other.

如果应用没有如期运行，你可以使用“Troubleshooting” 进行故障排除。If the app does not behave as you expect, you can troubleshoot the problem using the information in “Troubleshooting.”

扼要重述Recap

当你完成搜寻的实现，你已经完成了你的第三个iOS应用（一直在说的iCloud应用），祝贺！Now that you have completed the implementation of searching, you have completed your third iOS app. Congratulations!

花一会来考虑iCloud将如何影响你的应用框架。大部分需要支持iCloud的工作是在你的应用程序的数据部分。当你用一个UIDocument对象来管理你的文件，你所要做的工作量其实很小。Take a moment to think about how iCloud impacted your overall app architecture. Most of the work needed to support iCloud is in the data portion of your app. And when you use a UIDocument object to manage your files, the amount of work you have to do is actually small.