UIScreen类

摘要

最近无聊看了一下苹果的UIScreen类，发现好像除了使用[UIScreen mainScreen].bounds去获取获取屏幕的宽高外没有什么额外的用途。百度了一下，发现关于对它的介绍并不是很多，本着没人去翻译我就去打开个翻译软件翻译下的想法，打开了苹果的iOS Developer Library在UIKit框架里面找到了UIScreen_Class

官方介绍&翻译

A UIScreen object defines the properties associated with a hardware-based display. iOS devices have a main screen and zero or more attached screens. A tvOS device has a main screen for the television connected to the device. Use this class to obtain screen objects for each display attached to the device. Each screen object defines the bounds rectangle for the associated display and other interesting properties such as its brightness.

UIScreen对象定义了基于硬件显示的相关属性。iOS设备有一个主屏幕和零个或多个附带屏幕。tvOS设备有一个主屏幕，就是设备相连接的电视。使用这个类来获取每一个设备显示屏幕的对象。每一个屏幕对象定义了相关的边界矩形和其它有趣的属性，例如它的亮度。

Prior to iOS 8, a screen’s bounds rectangle always reflected the screen dimensions relative to a portrait-up orientation. Rotating the device to a landscape or upside-down orientation did not change the bounds. In iOS 8 and later, a screen’s bounds property takes the interface orientation of the screen into account. This behavior means that the bounds for a device in a portrait orientation may not be the same as the bounds for the device in a landscape orientation. Apps that rely on the screen dimensions can use the object in the fixedCoordinateSpace property as a fixed point of reference for any calculations they must make.

在iOS8之前，屏幕的bounds总能反映出屏幕尺寸，这个方向总是向上的，旋转设备和颠倒设备都不会改变。在iOS8之后，屏幕的bounds属性会被屏幕的方向而影响，这意味着设备的bounds在横屏的时候会不一样。如果App依赖于屏幕尺寸的话，可以使用fixedCoordinateSpace属性座位一个固定的参考点作为计算。

Handling Screen Connection and Disconnection Notifications

处理屏幕断开和连接的通知

When the user connects or disconnects a display to an iOS device, the system sends appropriate notifications to your app. Always observe the notifications from a long-lived object of your app, such as your app delegate. Connection and disconnection notifications can come at any time, even when your app is suspended in the background. If your app is suspended when a notification arrives, the notification is queued until your app starts running again in the foreground or background, at which point it is delivered to your observer object.

当用户连接或断开一个显示iOS的设备，系统会发送通知给App，使用一个长生命周期的对象去监听它，例如AppDelegate。在任何时候都有可能收到连接和断开的通知，甚至在你的App后台运行着。如果你的App暂停通知到来后,通知再次排队，直到你的App开始前台运行，它就会被送到你的观察者对象那里。

When you get a notification that a new external display is connected, use the extra screen space whenever you can. To use the space, create a window object, assign the new screen to its screen property, and show the window. Doing so causes the window’s contents to be displayed on the display when your app is in the foreground. If you do not create a window for the extra screen, or if you create a window but do not show it, a black field is displayed on the external display.

当你收到一个通知告诉你新的外部显示器已连接,你尽你所能去使用更多的屏幕空间。为了使用空间，你要创建一个窗口对象,分配新的屏幕的屏幕属性和去显示窗口。这样做会导致当你App前台运行时显示在窗口的内容。如果你不为额外的屏幕创建一个窗口,或者如果你创建一个窗口,但没有表现出来,一个黑色的字段显示在新的外部显示器。

handling connect and disconnect notifications shows two sampler handler methods for the connection and disconnection notifications. The connection handler creates a secondary window, associates it with the newly connected screen, asks one of the app’s view controllers (represented by the custom viewController property) to add some content to the window, and shows it. The disconnection handler releases the window and notifies the main view controller so that it can adjust its presentation accordingly.

处理连接和断开的通知告诉你两个简单处理通知的方法。连接处理的方法创建了一个二级窗口，将它与新连接的屏幕，询问其中一个应用程序的视图控制器(由自定义viewController属性)来添加一些内容的窗口，并显示它。断开处理的方法释放窗口和通知主要视图控制器，以便它可以相应地调整其界面。

Listing 1 Handling connect and disconnect notifications

- (void)handleScreenConnectNotification:(NSNotification*)aNotification {
    UIScreen*    newScreen = [aNotification object];
    CGRect        screenBounds = newScreen.bounds;
 
    if (!_secondWindow) {
        _secondWindow = [[UIWindow alloc] initWithFrame:screenBounds];
        _secondWindow.screen = newScreen;
 
        //设置并显示初始界面窗口
        [self.viewController displaySelectionInSecondaryWindow:_secondWindow];
        [_secondWindow makeKeyAndVisible];
    }
}
 
- (void)handleScreenDisconnectNotification:(NSNotification*)aNotification {
    if (_secondWindow) {
        //隐藏和删除窗口
        _secondWindow.hidden = YES;
        [_secondWindow release];
        _secondWindow = nil;
 
        //更新主屏幕的显示
        [self.viewController displaySelectionOnMainScreen];
    }
}

Configuring the Screen Mode of an External Display

配置外置屏幕显示模式

Many screens support multiple resolutions, some of which use different pixel aspect ratios. Screen objects use the most common screen mode by default, but you can change that mode to one that is more suitable for your content. For example, if you are implementing a game using OpenGL ES and your textures are designed for a 640 x 480 pixel screen, you might change the screen mode for screens with higher default resolutions.

多个屏幕支持多个分辨率，有一些使用不同的分辨率。屏幕对象在默认情况下使用常用的现实模式，但是你可以改变这一模式以适配你的内容。例如，如果你使用OpenGL ES去编写你的游戏，而游戏是根据640*480去设计的，你可能需要更改屏幕模式。

If you plan to use a screen mode other than the default one, apply that mode to the UIScreen object before associating the screen with a window. The UIScreenMode class defines the attributes of a single screen mode. You can get a list of the modes supported by a screen from its availableModes property and iterate through the list for one that matches your needs.

如果你打算使用一个非默认模式下的屏幕模式，在连接窗口之前你就应该更改完毕。UIScreenMode这个类定义一个单一的屏幕模式。你可以从它的availableModes属性中获取屏幕支持的模式列表，并在其中找到你所需要的模式。

For more information about screen modes, see UIScreenMode Class Reference.

想了解更多的屏幕模式，请看UIScreenMode类的介绍

Getting the Available Screens

获取可用的屏幕

• • mainScreen //类方法 返回主屏幕
• • screens //类方法 返回一个装有所有屏幕的数组
• mirroredScreen //属性 外部显示器的镜像(readonly)

Getting the Screen Coordinate Spaces

获取屏幕坐标空间

• coordinateSpace //属性 当前屏幕的坐标空间
• fixedCoordinateSpace //属性 被修正后的坐标空间

Getting the Bounds Information

获取边界矩形信息

• bounds //属性 屏幕的bounds
• applicationFrame //iOS9 属性 窗口的Frame
• nativeBounds //属性 物理屏幕的像素
• nativeScale //属性 设备物理屏幕的比例因子
• scale //属性 屏幕的设计比例因子

Accessing the Screen Modes

访问屏幕模式

• currentMode //属性 当前的屏幕模式
• preferredMode //属性 最佳的屏幕模式
• availableModes //属性 可用的屏幕模式

Getting a Display Link

获取一个显示连接

• • displayLinkWithTarget:selector: //对象方法 返回一个当前屏幕显示的链接对象

Setting a Display’s Brightness

设置显示亮度

• brightness //属性 屏幕亮度等级
• wantsSoftwareDimming //属性 使用软件改变亮度模式

Setting a Display’s Overscan Compensation

设置显示的扫描补偿

• overscanCompensation //属性 设置弥补过度扫描
• overscanCompensationInsets //属性 边缘嵌入值

Capturing a Screen Snapshot

捕捉屏幕快照

• • snapshotViewAfterScreenUpdates: //对象方法 返回一个基于当前屏幕的一个快照

Handling Focus Change on the Screen

处理改变屏幕的焦点

• focusedView //属性 当前焦点的视图
• supportsFocus //属性 判断是否支持遥控输入

Constants

常量

UIScreenOverscanCompensation

描述了不同的补偿技术在屏幕的边缘像素的损失。

typedef enum {
   UIScreenOverscanCompensationScale,
   UIScreenOverscanCompensationInsetBounds,
   UIScreenOverscanCompensationNone,
   UIScreenOverscanCompensationInsetApplicationFrame,
} UIScreenOverscanCompensation;

UIScreenOverscanCompensationScale //使所有像素在屏幕上可见。
UIScreenOverscanCompensationInsetBounds //屏幕范围缩小，所有像素在屏幕上是可见的。
UIScreenOverscanCompensationNone //没有发生补偿
UIScreenOverscanCompensationInsetApplicationFrame //缩小弥补过扫描，屏幕外的忽略

Notifications

通知

UIScreenDidConnectNotification

屏幕设备连接的通知

UIScreenDidDisconnectNotification

屏幕设备断开的通知

UIScreenModeDidChangeNotification

屏幕模式变更的通知

UIScreenBrightnessDidChangeNotification

屏幕亮度变更的通知

总结

经过了解发现，iOS开发并不常用到这个类，可能除了获取屏幕宽高以外的就是改变亮度了，但是做tvOS可能需要对这个类进行了解，因为这个类可以应对Apple TV连接断开电视的相关操作，而且能对屏幕进行优化！

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