基于iOS的车载视频客户端软件开发外文翻译资料-外文翻译网

苹果官方API翻译

1. UIImageView

A UIImageView object displays a single image or a sequence of animated images in your interface. Image views let you efficiently draw any image that can be specified using a UIImage object. For example, you can use this class to display the contents of many standard image files, such as JPEG and PNG files. You can configure image views programmatically or in your storyboard file and change the images they display at runtime. For animated images, you can also use the methods of this class to start and stop the animation and specify other animation parameters.

2. UIImage

A UIImage object manages image data in your app. You use image objects to represent image data of all kinds, and the UIImage class is capable of managing data for all image formats supported by the underlying platform. Image objects are immutable, so you always create them from existing image data, such as an image file on disk or programmatically created image data. An image object may contain a single image or a sequence of images you intend to use in an animation.

3. NSTimer

You use the NSTimer class to create timer objects or, more simply, timers. A timer waits until a certain time interval has elapsed and then fires, sending a specified message to a target object. For example, you could create an NSTimer object that sends a message to a window, telling it to update itself after a certain time interval.

Timers work in conjunction with run loops. To use a timer effectively, you should be aware of how run loops operate—see NSRunLoop and Threading Programming Guide. Note in particular that run loops maintain strong references to their timers, so you donrsquo;t have to maintain your own strong reference to a timer after you have added it to a run loop.

A timer is not a real-time mechanism; it fires only when one of the run loop modes to which the timer has been added is running and able to check if the timerrsquo;s firing time has passed. Because of the various input sources a typical run loop manages, the effective resolution of the time interval for a timer is limited to on the order of 50-100 milliseconds. If a timerrsquo;s firing time occurs during a long callout or while the run loop is in a mode that is not monitoring the timer, the timer does not fire until the next time the run loop checks the timer. Therefore, the actual time at which the timer fires potentially can be a significant period of time after the scheduled firing time. See also Timer Tolerance.

4. UIScrollView

UIScrollView is the superclass of several UIKit classes including UITableView and UITextView.

The central notion of a UIScrollView object (or, simply, a scroll view) is that it is a view whose origin is adjustable over the content view. It clips the content to its frame, which generally (but not necessarily) coincides with that of the applicationrsquo;s main window. A scroll view tracks the movements of fingers and adjusts the origin accordingly. The view that is showing its content “through” the scroll view draws that portion of itself based on the new origin, which is pinned to an offset in the content view. The scroll view itself does no drawing except for displaying vertical and horizontal scroll indicators. The scroll view must know the size of the content view so it knows when to stop scrolling; by default, it “bounces” back when scrolling exceeds the bounds of the content.

The object that manages the drawing of content displayed in a scroll view should tile the contentrsquo;s subviews so that no view exceeds the size of the screen. As users scroll in the scroll view, this object should add and remove subviews as necessary.

Because a scroll view has no scroll bars, it must know whether a touch signals an intent to scroll versus an intent to track a subview in the content. To make this determination, it temporarily intercepts a touch-down event by starting a timer and, before the timer fires, seeing if the touching finger makes any movement. If the timer fires without a significant change in position, the scroll view sends tracking events to the touched subview of the content view. If the user then drags their finger far enough before the timer elapses, the scroll view cancels any tracking in the subview and performs the scrolling itself. Subclasses can override the touchesShouldBegin:withEvent:inContentView:, pagingEnabled, and touchesShouldCancelInContentView: methods (which are called by the scroll view) to affect how the scroll view handles scrolling gestures.

A scroll view also handles zooming and panning of content. As the user makes a pinch-in or pinch-out gesture, the scroll view adjusts the offset and the scale of the content. When the gesture ends, the object managing the content view should should update subviews of the content as necessary. (Note that the gesture can end and a finger could still be down.) While the gesture is in progress, the scroll view does not send any tracking calls to the subview.

The UIScrollView class can have a delegate that must adopt the 苹果官方API翻译

UIImageView对象可以用来显示一个图像或者一组动画中的任意一个图像。使用者可以使用UIImage来制定任何你想展示的图像来添加到UIImageView上来进行显示。比如，使用者可以使用这个类来展示许多标准格式的图像文件，如JPEG和PNG文件的内容。对于动画图像，使用者也可以使用这个类的方法来开启和终止动画并修改其播放动画的其他一些参数。

UIImage对象是用来管理开发者应用程序中所涉及到的所有图像数据。使用它可以来表示应用程序中的各种各样的图像数据，以及能管理由底层平台支持的所有的图像数据。图像对象是不能被更改的，因此开发者只能从已存在的图像数据库中进行采用或者以此为基础加上图像编辑工具来创建。图像对象可以包含单个图像或打算在动画中使用的所有图像的。

开发者可以使用NSTimer类来创建Timer对象，或者更简单地说，计时器。定时器会在一定的时间之后触发一个事件，然后发送指定的消息给目标对象。例如，开发者在一个界面里设置一个定时器，并设置一定的时间，等时间一到就由定时器发送一个消息给下一个对象。

计时器不是实时机制，它的触发仅仅是该定时器已经增加了运行的循环模式，并且能够检查定时器是否已经运行了多场事件。由于一般的运行循环管理系统的计时器的时间间隔的有效分辨率被限制为50-100毫秒的数量级，所以让定时器触发潜在的可能是时间的预定时间开始计时后显著的时期。

该UIScrollView的类提供了显示内容和应用程序的窗口大小相适应的支持。它使用户可以通过滑动手势使其内容进行滚动，并通过捏手势使其进行放大和缩小。

用于管理内容的显示的对象需要保证滚动视图显示内容的子视图没有超过屏幕的边界。当用户在滚动视图滚动时，这个对象应该具有添加和删除子视图的功能。

滚动视图也具有放大和缩小其子视图的功能。当使用者要进行放大和缩小的操作时，滚动视图会调整其子视图的尺寸。当手势结束后，管理内容视图对象是根据其子视图来进行更新。（注意姿势可以结束，手指仍可能下降。）当手势正在进行，滚动视图不对其任何子视图进行监听。

5. UIPageControl

当用户点击一个页面控件移动到下一个或前一页，控制发送由委托处理UIControlEventValueChanged事件。然后委托可以评估当前页属性来确定显示页面。页面控制前进在任一方向只有一个页面。

UITabBarController类实现了通过底部标签来进行展示界面的视图控制器。通过底部所展示的标签，开发者可以将不同的设计方式放在标签所对应的界面当中，UITabBarController类所展示的是一种简单明了的视图控制器。

要配置一个标签栏控制器的选项卡，开发之必须指定视图控制器，使每个标签的viewControllers拥有属于自己的根视图。开发者指定的视图控制器的顺序决定了它们出现在标签栏的顺序。设置此属性时，开发者也应该给selectedViewController属性赋值，以用来指示哪个视图控制器的位置。当开发者需要给标签栏添加文本标签的时候，标签栏控制器会自动选择视图控制器和所要显示的内容来对这些进行调整。