【iOS翻译】App启动时的响应过程

　Responding to the Launch of Your App

　　Initialize your app’s data structures, prepare your app to run, and respond to any launch-time requests from the system.

　　初始化应用程序的数据结构、准备运行应用程序、响应系统启动时的一些请求。

　Overview 

　　The system launches your app when the user taps your app’s icon on the Home screen. If your app requested specific events, the system might also launch your app in the background to handle those events. For a scene-based app, the system similarly launches the app when one of your scenes needs to appear onscreen or do some work.

　　当用户点击桌面的应用程序图标时，系统就会运行你的应用程序，若是你的应用程序请求特定的事件，系统可能会在后台进行处理这些事件，而对于一个基于场景的应用程序，当一个场景须要出如今屏幕上或者作一些工做时，系统也会启动应用程序。

　　All apps have an associated process, represented by the UIApplication object. Apps also have an app delegate object—an object that conforms to the UIApplicationDelegateprotocol—whose job is to respond to important events happening within that process. Even a scene-based app uses an app delegate to manage fundamental events like launch and termination. At launch time, UIKit automatically creates the UIApplication object and your app delegate. It then starts your app’s main event loop.

　　全部的应用程序都有一个关联的进程，由UIApplication对象标识，应用程序也有一个委托对象（一个基于UIApplicationDelegate协议的对象，它的工做时响应进程执行中的重要事件），甚至一个基于场景的应用程序也使用应用程序委托对象来管理基本事件，在启动时，UIKit会自动建立UIApplication对象和委托代理。而后启动应用程序的主事件循环。

　Provide a Launch Storyboard

　　When the user first launches your app on a device, the system displays your launch storyboard until your app is ready to display its UI. Displaying the launch storyboard assures the user that your app launched and is doing something. If your app initializes itself and readies its UI quickly, the user may see your launch storyboard only briefly.

　　当用户第一次在设备上启动你的应用程序时，系统会显示启动故事板，直到程序准备好它的UI.显示故事板的目的是向用户保证你的应用程序已经启动，并且正在运行。　若是你的应用程序初始化的速度和准备的过程很是快，那用户可能只能短暂的看到你的启动故事板。

　　Xcode projects automatically include a default launch storyboard for you to customize, and you can add more launch storyboards as needed. To add new launch storyboards to your project, do the following:

　　Xcode项目会自动包含一个默认的启动故事板，但你能够根据须要添加更多的故事板，若是想添加新的启动故事板到项目中，须要作以下操做：

1. Open your project in Xcode.

2. Select File > New > New File.

3. Add a Launch Screen resource to your project.

　　Add views to your launch storyboard, and use Auto Layout constraints to size and position those views so that they adapt to the underlying environment. For example, you might create a splash screen with a solid-color background and a fixed-size image of your company logo or other content. Always create a final version of the interface you want. Never include temporary content or content that requires localization. UIKit displays exactly what you provide, using your constraints to fit your views into the available space.

　　添加视图到启动故事板中，使用自动布局约束来调整视图的大小和位置，以适应底层的环境。例如：你能够建立一个纯色的背景和固定大小的图片来标识你的公司logo，或者其余内容。始终建立所需接口的最终版本。不要包含临时内容或须要本地化的内容。精确地显示你所提供的，使用你的约束来说你的视图放入可用的空间。

　Important

　　In iOS 13 and later, always provide a launch storyboard for your app. Don’t use static launch images.

　　在iOS13及之后，老是提供一个故事板，再也不使用静态的启动图片。

 　Initialize Your App's Data Structures

　　Put your app's launch-time initialization code in one or both of the following methods:

　　将您的应用程序的启动时初始化代码放在如下一个或两个方法:

• application(_:willFinishLaunchingWithOptions:)

• application(_:didFinishLaunchingWithOptions:)

　　UIKit calls these methods at the beginning of your app’s launch cycle. Use them to:

　　UIKit在应用程序启动周期开始时调用这些方法。使用它们来作如下操做：

• Initialize your app's data structures.

• 初始化应用程序的结构

• Verify that your app has the resources it needs to run. 

• 验证应用程序运行所须要的资源

• Perform any one-time setup when your app is launched for the first time. For example, install templates or user-modifiable files in a writable directory; see Performing One-Time Setup for Your App. 

• 在应用程序第一次启动时执行任何一次性设置，例如：在可读写的目录中安装模板或用户可修改的文件。

• Connect to any critical services that your app uses. For example, connect to the Apple Push Notification service if your app supports remote notifications.

• 链接应用程序使用的任何关键服务。例如:若是你的应用程序支持远程推送通知，会链接到APNS.

• Check the launch options dictionary for information about why your app was launched; see Determine Why Your App Was Launched.

• 检查启动项字典信息。

　　For apps that aren't scene-based, UIKit loads your default user interface automatically at launch time. Use the application(_:didFinishLaunchingWithOptions:) method to make additional changes to that interface before it appears onscreen. For example, you might install a different view controller to reflect what the user was doing the last time they used the app.

　　对于不是基于场景的应用，UIKit在启动时默认加载用户界面。使用application(_:didFinishLaunchingWithOptions:)方法来作额外的更改。例如：你能够安装一个默认控制器来反应用户上一次使用应用程序作什么。

　　Move Long-Running Tasks off the Main Thread

　　When the user launches your app, make a good impression by launching quickly. UIKit doesn't present your app's interface until after the application(_:didFinishLaunchingWithOptions:) method returns. Performing long-running tasks in that method or your application(_:willFinishLaunchingWithOptions:) method might make your app appear sluggish to the user. Returning quickly is also important when launching to the background, because your app’s background execution time is limited. 

　　当用户启动应用程序时，经过快速启动来给用户留下一个好的印象。UIKit直到应用程序(_:didFinishLaunchingWithOptions:)方法返回后，才会显示用户界面，在该方法或(_:willFinishLaunchingWithOptions:)方法中执行耗时操做，可能会让用户以为你的应用程序运行缓慢。在启动到后台时，快速返回很重要，由于应用程序在后台执行时间有限。

　　Move tasks that are not critical to your app’s initialization out of the launch-time sequence. For example:

　　将对应用程序启动不重要的任务移出启动时间序列。例如：

• Defer the initialization of features that are not needed immediately.

• 推迟不须要的特性初始化。

• Move important, long-running tasks off your app’s main thread. For example, run them asynchronously on a global dispatch queue.

• 将重要的长时间运行的任务移出应用程序的主线程。例如：在全局调度队列中异步运行他们。

　Determine Why Your App Was Launched

　　When UIKit launches your app, it passes along a launch options dictionary to your application(_:willFinishLaunchingWithOptions:) and application(_:didFinishLaunchingWithOptions:) methods with information about why your app was launched. The keys in that dictionary indicate important tasks to perform immediately. For example, they might reflect actions that the user started elsewhere and want to continue in your app. Always check the contents of the launch options dictionary for keys that you expect, and respond appropriately to their presence.

　　当UIkit启动你的应用程序时，它会传递一个启动项字典给你的应用程序application(_:willFinishLaunchingWithOptions:) and application(_:didFinishLaunchingWithOptions:)方法，其中包含了为何启动。字典中的键标识当即执行的重要任务。例如：它们可能反应用户在其余地方启动的操做，并但愿在应用程序中继续执行。始终检查启动项字典的内容，查找您指望的键，并对它们作出适当的响应。

　Note

　　For a scene-based app, examine the options passed to the application(_:configurationForConnecting:options:) method to determine why your scene was created.

　　对于基于场景的应用程序，检查传递给应用程序(_:configurationforconnected:options:)方法的选项，以肯定为何建立场景。

　　Listing 1 shows the app delegate method for an app that handles background location updates. When the location key is present, the app starts location updates immediately, instead of deferring them until later. Starting location updates allows the Core Location framework to deliver the new location event.

　　清单1显示了处理后台位置更新的应用程序的应用程序委托方法。当位置键存在时，应用程序当即启动位置更新，而不是推迟到之后。启动位置更新容许核心位置框架交付新的位置事件。

class AppDelegate: UIResponder, UIApplicationDelegate, 
               CLLocationManagerDelegate {
    
   let locationManager = CLLocationManager()
   func application(_ application: UIApplication,
              didFinishLaunchingWithOptions launchOptions:
              [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
       
      // If launched because of new location data,
      //  start the visits service right away.
      if let keys = launchOptions?.keys {
         if keys.contains(.location) {
            locationManager.delegate = self
            locationManager.startMonitoringVisits()
         }
      }
       
      return true
   }
   // other methods…
}

　　The system doesn’t include a key unless your app supports the corresponding feature. For example, the system doesn’t include the remoteNotification key for an app that doesn’t support remote notifications. 

　　For a list of launch option keys and information about how to handle them, see UIApplication.LaunchOptionsKey.

　　除非你的应用程序支持相应的功能，不然系统不会包含密钥。例如，对于不支持远程通知的应用程序，系统不包含remoteNotification键。　　有关启动选项键的列表和有关如何处理它们的信息，请参见UIApplication.LaunchOptionsKey。