【移动应用开发技术】解析苹果官方文档之UIView Class Reference

【移动应用开发技术】［解析苹果官方文档］之［UIViewClassReference］

The

UIView

classdefinesarectangularareaonthescreenandtheinterfacesformanagingthecontentinthatarea.Atruntime,aviewobjecthandlestherenderingofanycontentinitsareaandalsohandlesanyinteractionswiththatcontent.The

UIView

classitselfprovidesbasicbehaviorforfillingitsrectangularareawithabackgroundcolor.Moresophisticatedcontentcanbepresentedbysubclassing

UIView

andimplementingthenecessarydrawingandevent-handlingcodeyourself.TheUIKitframeworkalsoincludesasetofstandardsubclassesthatrangefromsimplebuttonstocomplextablesandcanbeusedas-is.Forexample,a

UILabel

objectdrawsatextstringanda

UIImageView

objectdrawsanp_w_picpath.

UIView类定义了手机屏幕上的一块方形区域，并提供了管理此区域内模块内容的接口。程序运行时，view负责处理本视图区域内所有模块的渲染（render:(v.)

process

(anoutlinep_w_picpath)

using

colourandshading

inorder

tomakeitappear

solid

andthree-dimensional->

对轮廓图进行色彩及背景阴影处理，以产生三维立体实物效果），以及用户与这些模块之间的交互。UIView类本身就提供了为此方形区域填充背景色的基础方法。若想展现较为复杂的视图，我们可以创建子类，继承UIView，并按照自己的需求来实现(drawing)绘图以及(event-handling)事件处理的方法。UIKit框架也包含了一系列标准的UIView子类：从简单的UIButton到复杂的UITableView,这些类都可以拿来直接用。比如：UILabel对象->绘制一个字符串；UIImageView对象->绘制一张图片。Becauseviewobjectsarethemainwayyourapplicationinteractswiththeuser,theyhaveanumberofresponsibilities.Herearejustafew:

view对象是我们的应用与用户交互的主要途径，因此它有如下几项职责：DrawingandanimationViewsdrawcontentintheirrectangularareausingtechnologiessuchasUIKit,CoreGraphics,andOpenGLES.Someview

properties

canbeanimatedtonewvalues.

1).绘图＋动画view通过UIKit,CoreGraphics,OpenGLES等技术绘制方形区域的内容；view的某些属性值的改变可以赋与动画效果。LayoutandsubviewmanagementAviewmaycontainzeroormoresubviews.Eachviewdefinesitsowndefaultresizingbehaviorinrelationtoitsparentview.Aviewcandefinethesizeandpositionofitssubviewsasneeded.2).布局+子视图管理view可包含0或多个子视图；每个view都定义了在父视图大小发生变化时，重新调整自身大小的默认方法；view可以定义子视图的位置和大小。EventhandlingAviewisaresponderandcanhandletoucheventsandothereventsdefinedbythe

UIResponder

class.

Viewscanusethe

addGestureRecognizer:

methodtoinstallgesturerecognizerstohandlecommongestures.

3).事件处理UIView继承自UIResponder和NSObject;view本身就是一个responder，因此它能处理触摸点击事件或其他UIResponder类定义的事件；view可以通过addGestureRecognizer方法给视图加载手势识别器，处理常见的手势。Viewscanembedotherviewsandcreatesophisticatedvisualhierarchies.Thiscreatesaparent-childrelationshipbetweentheviewbeingembedded(knownasthe

subview)andtheparentviewdoingtheembedding(knownasthe

superview).Normally,asubview’svisibleareaisnotclippedtotheboundsofitssuperview,butiniOSyoucanusethe

clipsToBounds

propertytoalterthatbehavior.Aparentviewmaycontainanynumberofsubviewsbuteachsubviewhasonlyonesuperview,whichisresponsibleforpositioningitssubviewsappropriately.view可以重重嵌套，产生复杂的视图层级结构（在父视图superview之上嵌入子视图subview）。通常子视图的可视范围不会局限于父视图的边界，但我们可以修改clipToBounds属性值为yes将子视图超出父视图的部分裁剪掉不显示。父视图可以包含多个子视图，但每个子视图只能拥有一个父视图。父视图负责将子视图摆放在合适的位置。Thegeometryofaviewisdefinedbyits

frame,

bounds,and

center

properties.The

frame

definestheoriginanddimensionsoftheviewinthecoordinatesystemofitssuperviewandiscommonlyusedduringlayouttoadjustthesizeorpositionoftheview.The

center

propertycanbeusedtoadjustthepositionoftheviewwithoutchangingitssize.The

bounds

definestheinternaldimensionsoftheviewasitseesthemandisusedalmostexclusivelyincustomdrawingcode.Thesizeportionofthe

frame

and

bounds

rectanglesarecoupledtogethersothatchangingthesizeofeitherrectangleupdatesthesizeofboth.

view的几何属性由frame,bounds,center共同决定：frame:

view在其superview的坐标系中的起始位置frame.origin和尺寸frame.size；常用在布局中调整视图的方位和大小center:不改变view的大小，只调整view的位置bounds:view在自身坐标系中的尺寸；几乎只用于自定义绘图。frame.size和bounds.size是紧密相联的，任意一方改变，另一方均随之改变。Fordetailedinformationabouthowtousethe

UIView

class,see

ViewProgrammingGuideforiOS.

NOTEIniOS2.x,themaximumsizeofa

UIView

objectis1024x1024points.IniOS3.0andlater,viewsarenolongerrestrictedtothismaximumsizebutarestilllimitedbytheamountofmemorytheyconsume.Itisinyourbestintereststokeepviewsizesassmallaspossible.RegardlessofwhichversionofiOSisrunning,youshouldconsidertilinganycontentthatissignificantlylargerthanthedimensionsthescreen.

在iOS2.x系统中，视图对象的最大尺寸为1024*1024.但在iOS3.0及其之后的版本中，视图大小不再局限于这个数字，但仍旧受到所占用内存大小的限制。开发者最好将视图的大小设置得越小越好。不论运行的iOS是哪一版本，都应把比手机屏幕大很多的视图划分(tile)为小模块。CreatingaView

创建视图Tocreateaviewprogrammatically,youcanusecodelikethefollowing:CGRect

viewRect=CGRectMake(10,10,100,100);UIView*myView=[[UIViewalloc]initWithFrame:viewRect];Thiscodecreatestheviewandpositionsitatthepoint(10,10)initssuperview’scoordinatesystem(onceitisaddedtothatsuperview).Toaddasubviewtoanotherview,youusethe

addSubview:

method.IniOS,siblingviewsmayoverlapeachotherwithoutanyissues,allowingcomplexviewplacement.The

addSubview:

methodplacesthespecifiedviewontopofothersiblings.Youcanspecifytherelativez-orderofasubviewbyaddingitusingthe

insertSubview:aboveSubview:

and

insertSubview:belowSubview:

methods.Youcanalsoexchangethepositionofalreadyaddedsubviewsusingthe

exchangeSubviewAtIndex:withSubviewAtIndex:

method.

以代码方式创建视图：调用initWithFrame:方法；上述代码创建了一个视图，并将其在父视图坐标系统中的起始位置设置为了(10,10)点。我们通过调用addSubview:方法添加子视图。在iOS系统中，siblingviews(拥有相同的父视图)可以互相重叠，而且可以进行复杂的位置替换：addSubview:方法将某一特定视图覆盖于其他同级别的子视图(siblings)之上；insertSubview:aboveSubview:和insertSubview:belowSubview:方法指定视图在z坐标轴方向上的显示顺序；exchangeSubviewAtIndex:withSubviewAtIndex:方法调换两个同级别子视图之间的z坐标轴顺序。Whencreatingaview,itisimportanttoassignanappropriatevaluetothe

autoresizingMask

propertytoensuretheviewresizescorrectly.Viewresizingprimarilyoccurswhentheorientationofyourapplication’sinterfacechangesbutitmayhappenatothertimesaswell.Forexample,callingthe

setNeedsLayout

methodforcesyourviewtoupdateitslayout.

此段有关视图的autoresizingMask属性解析见此文：/4655765/1738641TheViewDrawingCycle视图的绘制周期Viewdrawingoccursonanas-neededbasis.Whenaviewisfirstshown,orwhenallorpartofitbecomesvisibleduetolayoutchanges,thesystemaskstheviewtodrawitscontents.ForviewsthatcontaincustomcontentusingUIKitorCoreGraphics,thesystemcallstheview’s

drawRect:

method.Yourimplementationofthismethodisresponsiblefordrawingtheview’scontentintothecurrentgraphicscontext,whichissetupbythesystemautomaticallypriortocallingthismethod.Thiscreatesa

staticvisualrepresentationofyourview’scontentthatcanthenbedisplayedonthescreen.

视图绘制仅在需要的时候才会进行。当某个视图首次显示，或其全部/部分内容由于布局变化从不可见状态变为可见状态时，系统将要求视图进行内容绘制。如果视图包含的是自定义的UIKit或CoreGraphics内容，系统会调用视图的drawRect:方法。我们在实现这个方法时，需要将视图的内容绘制到当前的绘图环境中去(这个绘图环境已经在调用drawRect:方法之前由系统自动搭建好了)，从而生成视图内容的静态可视界面，随后显示到屏幕上。Whentheactualcontentofyourviewchanges,itisyourresponsibilitytonotifythesystemthatyourviewneedstoberedrawn.Youdothisbycallingyourview’s

setNeedsDisplay

or

setNeedsDisplayInRect:

methodoftheview.Thesemethodsletthesystemknowthatitshouldupdatetheviewduringthenextdrawingcycle.Becauseitwaitsuntilthenextdrawingcycletoupdatetheview,youcancallthesemethodsonmultipleviewstoupdatethematthesametime.

此段有关视图的绘制周期解析见官方文档ViewProgrammingGuideforiOS章节。

略析见此文：/4655765/1738677NOTEIfyouareusingOpenGL

EStodoyourdrawing,youshouldusethe

GLKView

classinsteadofsubclassing

UIView.FormoreinformationabouthowtodrawusingOpenGL

ES,see

OpenGLESProgrammingGuideforiOS.

如果你使用的是OpenGLES框架绘图，你应该使用的是GLKView类，而不是继承自UIView类。详见官方文档OpenGLESProgrammingGuideforiOS章节。Animations动画Changestoseveralviewpropertiescanbeanimated—thatis,changingthepropertycreatesananimationthatconveysthechangetotheuseroverashortperiodoftime.The

UIView

classdoesmostoftheworkofperformingtheactualanimationsbutyoumuststillindicatewhichpropertychangesyouwanttobeanimated.Therearetwodifferentwaystoinitiateanimations:

IniOS4andlater,usetheblock-basedanimationmethods.(Recommended)Usethebegin/commitanimationmethods.

view的某些属性值的改变可以做出动画效果－将整个属性的变化过程在较短的时间内展示给用户。虽然UIView类负责大部分的动画操控，但开发者仍需要指定出哪些属性的改变是需要添加动画的。有两种开启动画的方式：1.在iOS4及之后的系统中，使用基于代码块block的动画方法（推荐）2.使用动画的begin、commit方法；Theblock-basedanimationmethods(suchas

animateWithDuration:animations:)greatlysimplifythecreationofanimations.Withonemethodcall,youspecifytheanimationstobeperformedandtheoptionsfortheanimation.However,block-basedanimationsareavailableonlyiniOS4andlater.IfyourapplicationrunsonearlierversionsofiOS,youmustusethe

beginAnimations:context:

and

commitAnimations

classmethodstomarkthebeginningandendingofyouranimations.

Thefollowingpropertiesofthe

UIView

classareanimatable:

基于代码块block的动画方法(例如animateWithDuration:animations:)极大简化了创建动画的步骤，只需在此方法中指定动画内容及动画选项这两个参数。但此方法仅适用于iOS4及以上的系统，对于老版本的系统则需要使用beginAnimations:context:和commitAnimations方法，它们分别标志着动画的开始和结束。UIView的以下属性都是可以加动画效果的：@property

frame@property

bounds@property

center@property

transform@property

alpha@property

backgroundColor@property

contentStretchFormoreinformationabouthowtoconfigureanimations,see

ViewProgrammingGuideforiOS.

有关视图的动画配置，详见官方文档ViewProgrammingGuideforiOS章节。ThreadingConsiderations涉及多线程的考虑Manipulationstoyourapplication’suserinterfacemustoccuronthemainthread.Thus,youshouldalwayscallthemethodsofthe

UIView

classfromcoderunninginthemainthreadofyourapplication.Theonlytimethismaynotbestrictlynecessaryiswhencreatingtheviewobjectitselfbutallothermanipulationsshouldoccuronthemainthread.

应用中所有的UI操作都必须在主线程中进行。除了创建视图的方法之外，其他所有UIView类中的方法都必须在主线程中被调用。SubclassingNotes关于子类的继承

The

UIView

classisakeysubclassingpointforvisualcontentthatalsorequiresuserinteractions.Althoughtherearemanygoodreasonstosubclass

UIView,itisrecommendedthatyoudosoonlywhenthebasic

UIView

classorthestandardsystemviewsdonotprovidethecapabilitiesthatyouneed.Subclassingrequiresmoreworkonyourparttoimplementtheviewandtotuneitsperformance.Forinformationaboutwaystoavoidsubclassing,see

AlternativestoSubclassing.

UIView的子类常用于实现视图展示和用户交互的双重效果。建议：如果UIView或系统已实现好的UIView子类可以满足你的需求，那就不要再自定义子类了。关于如何规避对子类的创建，参阅

AlternativestoSubclassing章节。MethodstoOverride可以重写的方法Whensubclassing

UIView,thereareonlyahandfulofmethodsyoushouldoverrideandmanymethodsthatyoumightoverridedependingonyourneeds.Because

UIView

isahighlyconfigurableclass,therearealsomanywaystoimplementsophisticatedviewbehaviorswithoutoverridingcustommethods,whicharediscussedintheAlternativestoSubclassingsection.Inthemeantime,thefollowinglistincludesthemethodsyoumightconsideroverridinginyour

UIView

subclasses:

创建UIView子类时，仅有为数不多的几个方法应该重写，剩下的很多方法则是根据自己的需要可重写可不重写。UIView具有很高的可配置度，也有很多种其他的途径可以代替实现复杂的视图结构，而不用重写方法。

以下这几个方法我们可以考虑是否需要重写：Initialization:初始化initWithFrame:

-Itisrecommendedthatyouimplementthismethod.Youcanalsoimplementcustominitializationmethodsinadditionto,orinsteadof,thismethod.initWithCoder:

-ImplementthismethodifyouloadyourviewfromanInterfaceBuildernibfileandyourviewrequirescustominitialization.layerClass

-ImplementthismethodonlyifyouwantyourviewtouseadifferentCoreAnimationlayerforitsbackingstore.Forexample,ifyourviewusestilingtodisplayalargescrollablearea,youmightwanttooverridethismethodandreturnthe

CATiledLayer

class.Drawingandprinting:绘图&打印drawRect:

-Implementthismethodifyourviewdrawscustomcontent.Ifyourviewdoesnotdoanycustomdrawing,avoidoverridingthismethod.

drawRect:forViewPrintFormatter:

-Implementthismethodonlyifyouwanttodrawyourview’scontentdifferentlyduringprinting.

Constraints:约束requiresConstraintBasedLayout

-Implementthisclassmethodifyourviewclassrequiresconstraintstoworkproperly.updateConstraints

-Implementthismethodifyourviewneedstocreatecustomconstraintsbetweenyoursubviews.alignmentRectForFrame:,

frameForAlignmentRect:

-Implementthesemethodstooverridehowyourviewsarealignedtootherviews.Layout:布局sizeThatFits:

-Implementthismethodifyouwantyourviewtohaveadifferentdefaultsizethanitnormallywouldduringresizingoperations.Forexample,youmightusethismethodtopreventyourviewfromshrinkingtothepointwheresubviewscannotbedisplayedcorrectly.

layoutSubviews

-Implementthismethodifyouneedmoreprecisecontroloverthelayoutofyoursubviewsthaneithertheconstraintorautoresizingbehaviorsprovide.

didAddSubview:,

willRemoveSubview:

-Implementthesemethodsasneededtotracktheadditionsandremovalsofsubviews.willMoveToSuperview:,

didMoveToSuperview

-Implementthesemethodsasneededtotrackthemovementofthecurrentviewinyourviewhierarchy.willMoveToWindow:,

didMoveToWindow

-Implementthesemethodsasneededtotrackthemovementofyourviewtoadifferentwindow.EventHandling:事件处理touchesBegan:withEvent:,

touchesMoved:withEvent:,

touchesEnded:withEvent:,

touchesCancelled:withEvent:

-Implementthesemethodsifyouneedtohandletoucheventsdirectly.(Forgesture-basedinput,usegesturerecognizers.)gestureRecognizerShouldBegin:

-Implementthismethodifyourviewhandlestoucheventsdirectlyandmightwanttopreventattachedgesturerecognizersfromtriggeringadditionalactions.AlternativestoSubclassing不用创建子类，还可以怎么做？Manyviewbehaviorscanbeconfiguredwithouttheneedforsubclassing.Beforeyoustartoverridingmethods,considerwhethermodifyingthefollowingpropertiesorbehaviorswouldprovidethebehavioryouneed.许多视图行为的实现都不用通过创建子类的方式，在重写部分方法之前，思考一下是否通过设置以下的属性就可以达到你想要的效果：addConstraint:

-Defineautomaticlayoutbehaviorfortheviewanditssubviews.addConstraint->

决定视图和子视图的自动布局行为autoresizingMask

-Providesautomaticlayoutbehaviorwhenthesuperview’sframechanges.Thesebehaviorscanbecombinedwithconstraints.autoresizingMask->当父视图的frame改变时，决定本视图的自动布局行为；可与上一个方法结合使用contentMode

-Provideslayoutbehaviorfortheview’scontent,asopposedtothe

frame

oftheview.Thispropertyalsoaffectshowthecontentisscaledtofittheviewandwhetheritiscachedorredrawn.

contentMode->

决定视图的bounds变化时，视图内容如何布局（对比frame属性）；此属性影响到视图的内容应该如何伸缩以适应本视图，以及视图是需要缓存还是重绘制。contentStretch

-Definesportionsoftheviewasbeingstretchable.Thisbehavioristypicallyusedtoimplementbuttonsandotherresizableviewswithsophisticatedlayoutneedswhereredrawingthevieweverytimewouldaffectperformance.contentStretch->决定视图的各部分是否可以伸缩。此行为通常用于实现按钮和其他大小可变的视图；这些视图的布局需求较为复杂，可能每次重新绘制视图时都会影响到性能表现。hidden

or

alpha

-Changethetransparencyoftheviewasawholeratherthanhidingorapplyingalphatoyourview’srenderedcontent.

hidden/alpha修改视图整体透明度，不用再隐藏/改变视图所渲染的某一部分内容的透明度backgroundColor

-Settheview’scolorratherthandrawingthatcoloryourself.backgroundColor直接设置视图颜色，省得再自行绘制Subviews-Ratherthandrawyourcontentusinga

drawRect:

method,embedp_w_picpathandlabelsubviewswiththecontentyouwanttopresent.

subviews->不用通过drawRect:方法绘制内容，可以考虑直接在p_w_picpath或label上叠放你想展示的子视图；Gesturerecognizers-Ratherthansubclasstointerceptandhandletoucheventsyourself,youcanusegesturerecognizerstosendan

actionmessage

toatargetobject.

gesturerecognizers->与其创建子类截获触屏事件，不如用gesturerecognizers发送action消息给target对象。Animations-Usethebuilt-i