文献翻译 -英文

苹果官方API翻译1. UIImageViewA 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. UIImageA 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. NSTimerYou 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 operatesee NSRunLoop and Threading Programming Guide. Note in particular that run loops maintain strong references to their timers, so you dont 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 timers 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 timers 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. UIScrollViewUIScrollView 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 applications 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 contents 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 UIScrollViewDelegate protocol. For zooming and panning to work, the delegate must implement both viewForZoomingInScrollView: and scrollViewDidEndZooming:withView:atScale:; in addition, the maximum (maximumZoomScale) and minimum ( minimumZoomScale) zoom scale must be different.5. UIPageControlThis application primarily demonstrates use of UIScrollViews paging functionality to use horizontal scrolling as a mechanism for navigating between different pages of content. With the iPad, this type of user interface is not really necessary since the screen is larger allowing for more content and detailed information.Designed as a universal application for both iPhone and iPad, this sample shows how to use two different sets of content, depending on which device the sample is running. The idea is that the iPhone uses a smaller set of images, while the iPad uses a larger set of images plus more detailed information. As a universal app this sample shows how to factor out these two types of UI and data based on the device.For the iPhone - The app uses UIScrollView and UIPageControl to move between pages. For the iPad - The app uses one large UIView with tiled pages, each page presenting a popover to display more detailed information.Based on the UIDevice idiom type, the UIApplication delegate loads two different set of nib files, one for the iPhone and the other for the iPad. To direct this kind of UI factoring, the sample uses a base class called ContentController. Subclasses of ContentController are used to support each device. Hence, the app loads two different user interfaces (or xibs) as well as two different sets of data driven by the ContentController.6. UITabBarControllerYou should never access the tab bar view of a tab bar controller directly. To configure the tabs of a tab bar controller, you assign the view controllers that provide the root view for each tab to the viewControllers property. The order in which you specify the view controllers determines the order in which they appear in the tab bar. When setting this property, you should also assign a value to the selectedViewController property to indicate which view controller is selected initially. (You can also select view controllers by array index using the selectedIndex property.) When you embed the tab bar controllers view (obtained using the inherited view property) in your application window, the tab bar controller automatically selects that view controller and displays its contents, resizing them as needed to fit the tab bar interface.Tab bar items are configured through their corresponding view controller. To associate a tab bar item with a view controller, create a new instance of the UITabBarItem class, configure it appropriately for the view controller, and assign it to the view controllers tabBarItem property. If you do not provide a custom tab bar item for your view controller, the view controller creates a default item containing no image and the text from the view controllers title property.As the user interacts with a tab bar interface, the tab bar controller object sends notifications about the interactions to its delegate. The delegate can be any object you specify but must conform to the UITabBarControllerDelegate protocol. You can use the delegate to prevent specific tab bar items from being selected and to perform additional tasks when tabs are selected. You can also use the delegate to monitor changes to the tab bar that are made by the More navigation controller, which is described in more detail in The More Navigation Controller.7. UITabBarA UITabBar object is a control for selecting between different subtasks, views, or modes in an app. Normally, you use tab bars in conjunction with a UITabBarController object, but you can also use them as standalone controls in your app. Tab bars always appear across the bottom edge of the screen and display the contents of one or more UITabBarItem objects. A tab bars appearance can be customized with a background image or tint color to suit the needs of your interface. Tapping an item selects and highlights that item, and you use the selection of the item to enable the corresponding mode for your app.You can configure tab bars programmatically or in Interface Builder. A UITabBarController object provides its own tab bar object and you must configure the object provided to you. When creating a tab bar programmatically, use the initWithFrame: method or another view initializer method to set its initial configuration. Use the methods of this class to configure the appearance of the tab bar. For tab bars you create yourself, you also use the methods of this class to specify the items displayed by the tab bar.8. UILabelThe UILabel class implements a read-only text view. You can use this class to draw one or multiple lines of static text, such as those you might use to identify other parts of your user interface. The base UILabel class provides support for both simple and complex styling of the label text. You can also control over aspects of appearance, such as whether the label uses a shadow or draws with a highlight. If needed, you can customize the appearance of your text further by subclassing.The default content mode of the UILabel class is UIViewContentModeRedraw. This mode causes the view to redraw its contents every time its bounding rectangle changes. You can change this mode by modifying the inherited contentMode property of the class.New label objects are configured to disregard user events and clip subviews by default. If you want to handle events in a custom subclass of UILabel, you must explicitly change the value of the userInteractionEnabled property to YES after initializing the object. If you want to allow subviews to extend beyond the bounds of a label, you must explicitly change the value of the labels clipsToBounds property to NO.9. UITextFieldA UITextField object displays an editable text area in your interface. You use text fields to gather text-based input from the user using the onscreen keyboard. The keyboard is configurable for many different types of input such as plain text, emails, numbers, and so on. Text fields use the target-action mechanism and a delegate object to report changes made during the course of editing.In addition to its basic text-editing behavior, you can add overlay views to a text field to display additional information and provide additional tappable controls. You might add custom overlay views for elements such as a bookmarks button or search icon. Text fields provide a built-in overlay view to clear the current text. The use of custom overlay views is optional.After adding a text field to your interface, you configure it for use in your app. Configuration involves performing some or all of the following tasks:(1)Configure one or more targets and actions for the text field.(2)Configure the keyboard-related attributes of the text field.(3)Assign a delegate object to handle important tasks, such as:(4)Determining whether the user should be allowed to edit the text fields contents.(5)Validating the text entered by the user.(6)Responding to taps in the keyboards return button.(7)Forwarding the user-entered text to other parts of your app.10. UIButtonA UIButton object is a view that executes your custom code in response to user interactions. When you tap a button, or select a button that has focus, the button performs any actions attached to it. You communicate the purpose of a button using a text label, an image, or both. The appearance of buttons is configurable, so you can tint buttons or format titles to match the design of your app. You can add buttons to your interface programmatically or using Interface Builder.When adding a button to your interface, perform the following steps:(1)Set the type of the button at creation time. (2)Supply a title string or image; size the button appropriately for your (3)content. (4)Connect one or more action methods to the button. (5)Set up Auto Layout rules to govern the size and position of the button in your interface. (6)Provide accessibility information and localized strings. 11. UITableViewAn instance of UITableView (or simply, a table view) is a means for displaying and editing hierarchical lists of information.A table view displays a list of items in a single column. UITableView is a subclass of UIScrollView, which allows users to scroll through the table, although UITableView allows vertical scrolling only. The cells comprising the individual items of the table are UITableViewCell objects; UITableView uses these objects to draw the visible rows of the table. Cells have contenttitles and imagesand can have, near the right edge, accessory views. Standard accessory views are disclosure indicators or detail disclosure buttons; the former leads to the next level in a data hierarchy and the latter leads to a detailed view of a selected item. Accessory views can also be framework controls, such as switches and sliders, or can be custom views. Table views can enter an editing mode where users can insert, delete, and reorder rows of the table.A table view is made up of zero or more sections, each with its own rows. Sections are identified by their index number within the table view, and rows are identified by their index number within a section. Any section can optionally be preceded by a section header, and optionally be followed by a section footer.Table views can have one of two styles, UITableViewStylePlain and UITableViewStyleGrouped. When you create a UITableView instance you must specify a table style, and this style cannot be changed. In the plain style, section headers and footers float above the content if the part of a complete section is visible. A table view can have an index that appears as a bar on the right hand side of the table (for example, A through Z). You can touch a particular label to jump to the target section. The grouped style of table view provides a default background color and a default background view for all cells. The background view provides a visual grouping for all cells in a particular section. For example, one group could be a persons name and title, another group for phone numbers that the person uses, and another group for email accounts and so on. See the Settings application for examples of grouped tables. Table views in the grouped style cannot have an index.Many methods of UITableView take NSIndexPath objects as parameters and return values. UITableView declares a category on NSIndexPath that enables you to get the represented row index (row property) and section index (section property), and to construct an index path from a given row index and section index (indexPathForRow:inSection: method). Especially in table views with multiple sections, you must evaluate the section index before identifying a row by its index number.A UITableView object must have an object that acts as a data source and an object that acts as a delegate; typically these objects are either the application delegate or, more frequently, a custom UITableViewController object. The data source must adopt the UITableViewDataSource protocol and the delegate must adopt the UITableViewDelegate protocol. The data source provides information that UITableView needs to construct tables and manages the data model when rows of a table are inserted, deleted, or reordered. The delegate manages table row configuration and selection, row reordering, highlighting, accessory views, and editing operations.When sent a setEditing:animated: message (with a first parameter of YES), the table view enters into editing mode where it shows the editing or reordering controls of each visible row, depending on the editingStyle of each associated UITableViewCell. Clicking on the insertion or deletion control causes the data source to receive a tableView:commitEditingStyle:forRowAtIndexPath: message. You commit a deletion or insertion by calling deleteRowsAtIndexPaths:withRowAnimation: or insertRowsAtIndexPaths:withRowAnimation:, as appropriate. Also in editing mode, if a table-view cell has its showsReorderControl property set to YES, the data source receives a tableView:moveRowAtIndexPath:toIndexPath: message. The data source can selectively remove the reordering control for cells by implementing tableView:canMoveRowAtIndexPath:.UITableView caches table-view cells for visible rows. You can create custom UITableViewCell objects with content or behavioral characteristics that are different than the default cells; A Closer Look at Table View Cells explains how.UITableView overrides the layoutSubviews method of UIView so that it calls reloadData only when you create a new instance of UITableView or when you assign a new data source. Reloading the table view clears current state, including the current selection. Howeve