文献翻译英文Word格式文档下载.docx

文献翻译英文Word格式文档下载.docx

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1.UIImageView

AUIImageViewobjectdisplaysasingleimageorasequenceofanimatedimagesinyourinterface.ImageviewsletyouefficientlydrawanyimagethatcanbespecifiedusingaUIImageobject.Forexample,youcanusethisclasstodisplaythecontentsofmanystandardimagefiles,suchasJPEGandPNGfiles.Youcanconfigureimageviewsprogrammaticallyorinyourstoryboardfileandchangetheimagestheydisplayatruntime.Foranimatedimages,youcanalsousethemethodsofthisclasstostartandstoptheanimationandspecifyotheranimationparameters.

2.UIImage

AUIImageobjectmanagesimagedatainyourapp.Youuseimageobjectstorepresentimagedataofallkinds,andtheUIImageclassiscapableofmanagingdataforallimageformatssupportedbytheunderlyingplatform.Imageobjectsareimmutable,soyoualwayscreatethemfromexistingimagedata,suchasanimagefileondiskorprogrammaticallycreatedimagedata.Animageobjectmaycontainasingleimageorasequenceofimagesyouintendtouseinananimation.

3.NSTimer

YouusetheNSTimerclasstocreatetimerobjectsor,moresimply,timers.Atimerwaitsuntilacertaintimeintervalhaselapsedandthenfires,sendingaspecifiedmessagetoatargetobject.Forexample,youcouldcreateanNSTimerobjectthatsendsamessagetoawindow,tellingittoupdateitselfafteracertaintimeinterval.

Timersworkinconjunctionwithrunloops.Touseatimereffectively,youshouldbeawareofhowrunloopsoperate—seeNSRunLoopandThreadingProgrammingGuide.Noteinparticularthatrunloopsmaintainstrongreferencestotheirtimers,soyoudon’thavetomaintainyourownstrongreferencetoatimerafteryouhaveaddedittoarunloop.

Atimerisnotareal-timemechanism;

itfiresonlywhenoneoftherunloopmodestowhichthetimerhasbeenaddedisrunningandabletocheckifthetimer’sfiringtimehaspassed.Becauseofthevariousinputsourcesatypicalrunloopmanages,theeffectiveresolutionofthetimeintervalforatimerislimitedtoontheorderof50-100milliseconds.Ifatimer’sfiringtimeoccursduringalongcalloutorwhiletherunloopisinamodethatisnotmonitoringthetimer,thetimerdoesnotfireuntilthenexttimetherunloopchecksthetimer.Therefore,theactualtimeatwhichthetimerfirespotentiallycanbeasignificantperiodoftimeafterthescheduledfiringtime.SeealsoTimerTolerance.

4.UIScrollView

UIScrollViewisthesuperclassofseveralUIKitclassesincludingUITableViewandUITextView.

ThecentralnotionofaUIScrollViewobject（or,simply,ascrollview）isthatitisaviewwhoseoriginisadjustableoverthecontentview.Itclipsthecontenttoitsframe,whichgenerally（butnotnecessarily）coincideswiththatoftheapplication’smainwindow.Ascrollviewtracksthemovementsoffingersandadjuststheoriginaccordingly.Theviewthatisshowingitscontent“through”thescrollviewdrawsthatportionofitselfbasedontheneworigin,whichispinnedtoanoffsetinthecontentview.Thescrollviewitselfdoesnodrawingexceptfordisplayingverticalandhorizontalscrollindicators.Thescrollviewmustknowthesizeofthecontentviewsoitknowswhentostopscrolling;

bydefault,it“bounces”backwhenscrollingexceedstheboundsofthecontent.

Theobjectthatmanagesthedrawingofcontentdisplayedinascrollviewshouldtilethecontent’ssubviewssothatnoviewexceedsthesizeofthescreen.Asusersscrollinthescrollview,thisobjectshouldaddandremovesubviewsasnecessary.

Becauseascrollviewhasnoscrollbars,itmustknowwhetheratouchsignalsanintenttoscrollversusanintenttotrackasubviewinthecontent.Tomakethisdetermination,ittemporarilyinterceptsatouch-downeventbystartingatimerand,beforethetimerfires,seeingifthetouchingfingermakesanymovement.Ifthetimerfireswithoutasignificantchangeinposition,thescrollviewsendstrackingeventstothetouchedsubviewofthecontentview.Iftheuserthendragstheirfingerfarenoughbeforethetimerelapses,thescrollviewcancelsanytrackinginthesubviewandperformsthescrollingitself.SubclassescanoverridethetouchesShouldBegin:

withEvent:

inContentView:

pagingEnabled,andtouchesShouldCancelInContentView:

methods（whicharecalledbythescrollview）toaffecthowthescrollviewhandlesscrollinggestures.

Ascrollviewalsohandleszoomingandpanningofcontent.Astheusermakesapinch-inorpinch-outgesture,thescrollviewadjuststheoffsetandthescaleofthecontent.Whenthegestureends,theobjectmanagingthecontentviewshouldshouldupdatesubviewsofthecontentasnecessary.（Notethatthegesturecanendandafingercouldstillbedown.）Whilethegestureisinprogress,thescrollviewdoesnotsendanytrackingcallstothesubview.

TheUIScrollViewclass