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，如果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，当一个场景需要出现在屏幕上或者做一些工作时，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.

所有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，它的工作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会自动创建UIApplication对象和委托代理。然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，而且正在运行。　如果你的应用程序初始化的速度和准备的过程非常快，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，但你可以根据需要添加更多的故事板，如果想添加新的启动故事板到项目中，需要做如下操作：

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：你可以创建一个纯色的背景和固定大小的图片来标识你的公司logo，或者其他内容。始终创建所需接口的最终版本。不要包含临时内容或需要本地化的内容。精确地显示你所提供的，使用你的约束来讲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及以后，总是提供一个故事板，不再使用静态的启动图片。

 　Initialize Your App‘s Data Structures

　　Move Long-Running Tasks off the Main Thread

　Determine Why Your App Was Launched

　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，以确定为什么创建场景。

　　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，应用程序立即启动位置更新，而不是推迟到以后。启动位置更新允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，否则系统不会包含密钥。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。