【移動應用開發技術】解析蘋果官方文檔之UIView Class Reference

【移動應用開發技術】［解析蘋果官方文檔］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類定義了手機屏幕上的一塊方形區域，并提供了管理此區域內模塊內容的接口。程序運行時，view負責處理本視圖區域內所有模塊的渲染（render:(v.)

process

(anoutlinep_w_picpath)

using

colourandshading

inorder

tomakeitappear

solid

andthree-dimensional->

對輪廓圖進行色彩及背景陰影處理，以產生三維立體實物效果），以及用戶與這些模塊之間的交互。UIView類本身就提供了為此方形區域填充背景色的基礎方法。若想展現較為復雜的視圖，我們可以創建子類，繼承UIView，并按照自己的需求來實現(drawing)繪圖以及(event-handling)事件處理的方法。UIKit框架也包含了一系列標準的UIView子類：從簡單的UIButton到復雜的UITableView,這些類都可以拿來直接用。比如：UILabel對象->繪制一個字符串；UIImageView對象->繪制一張圖片。Becauseviewobjectsarethemainwayyourapplicationinteractswiththeuser,theyhaveanumberofresponsibilities.Herearejustafew:

view對象是我們的應用與用戶交互的主要途徑，因此它有如下幾項職責：DrawingandanimationViewsdrawcontentintheirrectangularareausingtechnologiessuchasUIKit,CoreGraphics,andOpenGLES.Someview

properties

canbeanimatedtonewvalues.

1).繪圖＋動畫view通過UIKit,CoreGraphics,OpenGLES等技術繪制方形區域的內容；view的某些屬性值的改變可以賦與動畫效果。LayoutandsubviewmanagementAviewmaycontainzeroormoresubviews.Eachviewdefinesitsowndefaultresizingbehaviorinrelationtoitsparentview.Aviewcandefinethesizeandpositionofitssubviewsasneeded.2).布局+子視圖管理view可包含0或多個子視圖；每個view都定義了在父視圖大小發生變化時，重新調整自身大小的默認方法；view可以定義子視圖的位置和大小。EventhandlingAviewisaresponderandcanhandletoucheventsandothereventsdefinedbythe

UIResponder

class.

Viewscanusethe

addGestureRecognizer:

methodtoinstallgesturerecognizerstohandlecommongestures.

3).事件處理UIView繼承自UIResponder和NSObject;view本身就是一個responder，因此它能處理觸摸點擊事件或其他UIResponder類定義的事件；view可以通過addGestureRecognizer方法給視圖加載手勢識別器，處理常見的手勢。Viewscanembedotherviewsandcreatesophisticatedvisualhierarchies.Thiscreatesaparent-childrelationshipbetweentheviewbeingembedded(knownasthe

subview)andtheparentviewdoingtheembedding(knownasthe

superview).Normally,asubview’svisibleareaisnotclippedtotheboundsofitssuperview,butiniOSyoucanusethe

clipsToBounds

propertytoalterthatbehavior.Aparentviewmaycontainanynumberofsubviewsbuteachsubviewhasonlyonesuperview,whichisresponsibleforpositioningitssubviewsappropriately.view可以重重嵌套，產生復雜的視圖層級結構（在父視圖superview之上嵌入子視圖subview）。通常子視圖的可視范圍不會局限于父視圖的邊界，但我們可以修改clipToBounds屬性值為yes將子視圖超出父視圖的部分裁剪掉不顯示。父視圖可以包含多個子視圖，但每個子視圖只能擁有一個父視圖。父視圖負責將子視圖擺放在合適的位置。Thegeometryofaviewisdefinedbyits

frame,

bounds,and

center

properties.The

frame

definestheoriginanddimensionsoftheviewinthecoordinatesystemofitssuperviewandiscommonlyusedduringlayouttoadjustthesizeorpositionoftheview.The

center

propertycanbeusedtoadjustthepositionoftheviewwithoutchangingitssize.The

bounds

definestheinternaldimensionsoftheviewasitseesthemandisusedalmostexclusivelyincustomdrawingcode.Thesizeportionofthe

frame

and

bounds

rectanglesarecoupledtogethersothatchangingthesizeofeitherrectangleupdatesthesizeofboth.

view的幾何屬性由frame,bounds,center共同決定：frame:

view在其superview的坐標系中的起始位置frame.origin和尺寸frame.size；常用在布局中調整視圖的方位和大小center:不改變view的大小，只調整view的位置bounds:view在自身坐標系中的尺寸；幾乎只用于自定義繪圖。frame.size和bounds.size是緊密相聯的，任意一方改變，另一方均隨之改變。Fordetailedinformationabouthowtousethe

UIView

class,see

ViewProgrammingGuideforiOS.

NOTEIniOS2.x,themaximumsizeofa

UIView

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

在iOS2.x系統中，視圖對象的最大尺寸為1024*1024.但在iOS3.0及其之后的版本中，視圖大小不再局限于這個數字，但仍舊受到所占用內存大小的限制。開發者最好將視圖的大小設置得越小越好。不論運行的iOS是哪一版本，都應把比手機屏幕大很多的視圖劃分(tile)為小模塊。CreatingaView

創建視圖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.

以代碼方式創建視圖：調用initWithFrame:方法；上述代碼創建了一個視圖，并將其在父視圖坐標系統中的起始位置設置為了(10,10)點。我們通過調用addSubview:方法添加子視圖。在iOS系統中，siblingviews(擁有相同的父視圖)可以互相重疊，而且可以進行復雜的位置替換：addSubview:方法將某一特定視圖覆蓋于其他同級別的子視圖(siblings)之上；insertSubview:aboveSubview:和insertSubview:belowSubview:方法指定視圖在z坐標軸方向上的顯示順序；exchangeSubviewAtIndex:withSubviewAtIndex:方法調換兩個同級別子視圖之間的z坐標軸順序。Whencreatingaview,itisimportanttoassignanappropriatevaluetothe

autoresizingMask

propertytoensuretheviewresizescorrectly.Viewresizingprimarilyoccurswhentheorientationofyourapplication’sinterfacechangesbutitmayhappenatothertimesaswell.Forexample,callingthe

setNeedsLayout

methodforcesyourviewtoupdateitslayout.

此段有關視圖的autoresizingMask屬性解析見此文：/4655765/1738641TheViewDrawingCycle視圖的繪制周期Viewdrawingoccursonanas-neededbasis.Whenaviewisfirstshown,orwhenallorpartofitbecomesvisibleduetolayoutchanges,thesystemaskstheviewtodrawitscontents.ForviewsthatcontaincustomcontentusingUIKitorCoreGraphics,thesystemcallstheview’s

drawRect:

method.Yourimplementationofthismethodisresponsiblefordrawingtheview’scontentintothecurrentgraphicscontext,whichissetupbythesystemautomaticallypriortocallingthismethod.Thiscreatesa

staticvisualrepresentationofyourview’scontentthatcanthenbedisplayedonthescreen.

視圖繪制僅在需要的時候才會進行。當某個視圖首次顯示，或其全部/部分內容由于布局變化從不可見狀態變為可見狀態時，系統將要求視圖進行內容繪制。如果視圖包含的是自定義的UIKit或CoreGraphics內容，系統會調用視圖的drawRect:方法。我們在實現這個方法時，需要將視圖的內容繪制到當前的繪圖環境中去(這個繪圖環境已經在調用drawRect:方法之前由系統自動搭建好了)，從而生成視圖內容的靜態可視界面，隨后顯示到屏幕上。Whentheactualcontentofyourviewchanges,itisyourresponsibilitytonotifythesystemthatyourviewneedstoberedrawn.Youdothisbycallingyourview’s

setNeedsDisplay

or

setNeedsDisplayInRect:

methodoftheview.Thesemethodsletthesystemknowthatitshouldupdatetheviewduringthenextdrawingcycle.Becauseitwaitsuntilthenextdrawingcycletoupdatetheview,youcancallthesemethodsonmultipleviewstoupdatethematthesametime.

此段有關視圖的繪制周期解析見官方文檔ViewProgrammingGuideforiOS章節。

略析見此文：/4655765/1738677NOTEIfyouareusingOpenGL

EStodoyourdrawing,youshouldusethe

GLKView

classinsteadofsubclassing

UIView.FormoreinformationabouthowtodrawusingOpenGL

ES,see

OpenGLESProgrammingGuideforiOS.

如果你使用的是OpenGLES框架繪圖，你應該使用的是GLKView類，而不是繼承自UIView類。詳見官方文檔OpenGLESProgrammingGuideforiOS章節。Animations動畫Changestoseveralviewpropertiescanbeanimated—thatis,changingthepropertycreatesananimationthatconveysthechangetotheuseroverashortperiodoftime.The

UIView

classdoesmostoftheworkofperformingtheactualanimationsbutyoumuststillindicatewhichpropertychangesyouwanttobeanimated.Therearetwodifferentwaystoinitiateanimations:

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

view的某些屬性值的改變可以做出動畫效果－將整個屬性的變化過程在較短的時間內展示給用戶。雖然UIView類負責大部分的動畫操控，但開發者仍需要指定出哪些屬性的改變是需要添加動畫的。有兩種開啟動畫的方式：1.在iOS4及之后的系統中，使用基于代碼塊block的動畫方法（推薦）2.使用動畫的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:

基于代碼塊block的動畫方法(例如animateWithDuration:animations:)極大簡化了創建動畫的步驟，只需在此方法中指定動畫內容及動畫選項這兩個參數。但此方法僅適用于iOS4及以上的系統，對于老版本的系統則需要使用beginAnimations:context:和commitAnimations方法，它們分別標志著動畫的開始和結束。UIView的以下屬性都是可以加動畫效果的：@property

frame@property

bounds@property

center@property

transform@property

alpha@property

backgroundColor@property

contentStretchFormoreinformationabouthowtoconfigureanimations,see

ViewProgrammingGuideforiOS.

有關視圖的動畫配置，詳見官方文檔ViewProgrammingGuideforiOS章節。ThreadingConsiderations涉及多線程的考慮Manipulationstoyourapplication’suserinterfacemustoccuronthemainthread.Thus,youshouldalwayscallthemethodsofthe

UIView

classfromcoderunninginthemainthreadofyourapplication.Theonlytimethismaynotbestrictlynecessaryiswhencreatingtheviewobjectitselfbutallothermanipulationsshouldoccuronthemainthread.

應用中所有的UI操作都必須在主線程中進行。除了創建視圖的方法之外，其他所有UIView類中的方法都必須在主線程中被調用。SubclassingNotes關于子類的繼承

The

UIView

classisakeysubclassingpointforvisualcontentthatalsorequiresuserinteractions.Althoughtherearemanygoodreasonstosubclass

UIView,itisrecommendedthatyoudosoonlywhenthebasic

UIView

classorthestandardsystemviewsdonotprovidethecapabilitiesthatyouneed.Subclassingrequiresmoreworkonyourparttoimplementtheviewandtotuneitsperformance.Forinformationaboutwaystoavoidsubclassing,see

AlternativestoSubclassing.

UIView的子類常用于實現視圖展示和用戶交互的雙重效果。建議：如果UIView或系統已實現好的UIView子類可以滿足你的需求，那就不要再自定義子類了。關于如何規避對子類的創建，參閱

AlternativestoSubclassing章節。MethodstoOverride可以重寫的方法Whensubclassing

UIView,thereareonlyahandfulofmethodsyoushouldoverrideandmanymethodsthatyoumightoverridedependingonyourneeds.Because

UIView

isahighlyconfigurableclass,therearealsomanywaystoimplementsophisticatedviewbehaviorswithoutoverridingcustommethods,whicharediscussedintheAlternativestoSubclassingsection.Inthemeantime,thefollowinglistincludesthemethodsyoumightconsideroverridinginyour

UIView

subclasses:

創建UIView子類時，僅有為數不多的幾個方法應該重寫，剩下的很多方法則是根據自己的需要可重寫可不重寫。UIView具有很高的可配置度，也有很多種其他的途徑可以代替實現復雜的視圖結構，而不用重寫方法。

以下這幾個方法我們可以考慮是否需要重寫：Initialization:初始化initWithFrame:

-Itisrecommendedthatyouimplementthismethod.Youcanalsoimplementcustominitializationmethodsinadditionto,orinsteadof,thismethod.initWithCoder:

-ImplementthismethodifyouloadyourviewfromanInterfaceBuildernibfileandyourviewrequirescustominitialization.layerClass

-ImplementthismethodonlyifyouwantyourviewtouseadifferentCoreAnimationlayerforitsbackingstore.Forexample,ifyourviewusestilingtodisplayalargescrollablearea,youmightwanttooverridethismethodandreturnthe

CATiledLayer

class.Drawingandprinting:繪圖&打印drawRect:

-Implementthismethodifyourviewdrawscustomcontent.Ifyourviewdoesnotdoanycustomdrawing,avoidoverridingthismethod.

drawRect:forViewPrintFormatter:

-Implementthismethodonlyifyouwanttodrawyourview’scontentdifferentlyduringprinting.

Constraints:約束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:事件處理touchesBegan:withEvent:,

touchesMoved:withEvent:,

touchesEnded:withEvent:,

touchesCancelled:withEvent:

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

-Implementthismethodifyourviewhandlestoucheventsdirectlyandmightwanttopreventattachedgesturerecognizersfromtriggeringadditionalactions.AlternativestoSubclassing不用創建子類，還可以怎么做？Manyviewbehaviorscanbeconfiguredwithouttheneedforsubclassing.Beforeyoustartoverridingmethods,considerwhethermodifyingthefollowingpropertiesorbehaviorswouldprovidethebehavioryouneed.許多視圖行為的實現都不用通過創建子類的方式，在重寫部分方法之前，思考一下是否通過設置以下的屬性就可以達到你想要的效果：addConstraint:

-Defineautomaticlayoutbehaviorfortheviewanditssubviews.addConstraint->

決定視圖和子視圖的自動布局行為autoresizingMask

-Providesautomaticlayoutbehaviorwhenthesuperview’sframechanges.Thesebehaviorscanbecombinedwithconstraints.autoresizingMask->當父視圖的frame改變時，決定本視圖的自動布局行為；可與上一個方法結合使用contentMode

-Provideslayoutbehaviorfortheview’scontent,asopposedtothe

frame

oftheview.Thispropertyalsoaffectshowthecontentisscaledtofittheviewandwhetheritiscachedorredrawn.

contentMode->

決定視圖的bounds變化時，視圖內容如何布局（對比frame屬性）；此屬性影響到視圖的內容應該如何伸縮以適應本視圖，以及視圖是需要緩存還是重繪制。contentStretch

-Definesportionsoftheviewasbeingstretchable.Thisbehavioristypicallyusedtoimplementbuttonsandotherresizableviewswithsophisticatedlayoutneedswhereredrawingthevieweverytimewouldaffectperformance.contentStretch->決定視圖的各部分是否可以伸縮。此行為通常用于實現按鈕和其他大小可變的視圖；這些視圖的布局需求較為復雜，可能每次重新繪制視圖時都會影響到性能表現。hidden

or

alpha

-Changethetransparencyoftheviewasawholeratherthanhidingorapplyingalphatoyourview’srenderedcontent.

hidden/alpha修改視圖整體透明度，不用再隱藏/改變視圖所渲染的某一部分內容的透明度backgroundColor

-Settheview’scolorratherthandrawingthatcoloryourself.backgroundColor直接設置視圖顏色，省得再自行繪制Subviews-Ratherthandrawyourcontentusinga

drawRect:

method,embedp_w_picpathandlabelsubviewswiththecontentyouwanttopresent.

subviews->不用通過drawRect:方法繪制內容，可以考慮直接在p_w_picpath或label上疊放你想展示的子視圖；Gesturerecognizers-Ratherthansubclasstointerceptandhandletoucheventsyourself,youcanusegesturerecognizerstosendan

actionmessage

toatargetobject.

gesturerecognizers->與其創建子類截獲觸屏事件，不如用gesturerecognizers發送action消息給target對象。Animations-Usethebuilt-i