【移動(dòng)應(yīng)用開(kāi)發(fā)技術(shù)】App Launch time 101 (Android Performance Patterns Season 6 Ep. 1)

【移動(dòng)應(yīng)用開(kāi)發(fā)技術(shù)】AppLaunchtime101(AndroidPerformancePatternsSeason6Ep.1)

Youknowwhatthistimermeans?Everyquartersecondauserspendsstaringatablankscreeninsteadofinterfacingwithyourappisaquartersecondmore.they'rewillingtocloseyourappandgivetheirattentiontosomethingelse.misunderstandingallthecomplexthingsthathappenduringyourappstartupcanleadtosomeseriousperformanceproblems.

Now,see,Androidisprettysmartwhenitcomestounderstandinghumanperformanceperception.Assoonastheuserlaunchesyourapplication,Androidwillimmediatelydisplayastartwindow,whichwillstayarounduntillyourapplicationisfully

loaded,initialized,andcandrawitsfirstframe.--你知道這個(gè)計(jì)時(shí)器是什么意思嗎？【這個(gè)不知道怎么翻譯，大概意思就是說(shuō)如果啟動(dòng)時(shí)的白屏界面時(shí)間過(guò)長(zhǎng)】。他們會(huì)希望把你的app關(guān)了，然后去做別的事情。在app啟動(dòng)過(guò)程中的那些復(fù)雜錯(cuò)誤的操作會(huì)導(dǎo)致一些嚴(yán)重的性能問(wèn)題。

現(xiàn)在我們了解了，android其實(shí)是很聰明的，它能夠明白人類對(duì)性能的感知。一旦用戶點(diǎn)擊桌面圖標(biāo)，android會(huì)立即展示啟動(dòng)窗口，這個(gè)窗口將持續(xù)，直到你的應(yīng)用完全加載，初始化，繪制首幀。

Thisbehaviorismostoftenseenwhenyourappisbootedforthefirsttime,butitcaneasilyhappenothertimesaswell,likewhentheactivityisbroughttotheforeground,oraftertheuserbacksoutofyourapp,oraftersomeportionofyourapphasbeenpurgedbythesystemtosavememory.Basically,anytimetheusermovesfromsomethingelsetoyourapplication,there'sachanceyoucanseethistypeofbehavior.--這種情況在在app冷啟動(dòng)時(shí)候很常見(jiàn)，但是也很容易發(fā)生在其他時(shí)候，比如活動(dòng)被置于前臺(tái)，或者用于退出你的app，或者你的app的某些部分被系統(tǒng)清楚用于節(jié)省內(nèi)存。基本上，任何時(shí)候，用戶向你的應(yīng)用轉(zhuǎn)移一些東西（應(yīng)該是指調(diào)用你的app），你也有機(jī)會(huì)看到這種情況。****套用知乎：coldstart：應(yīng)用第一次啟動(dòng)。

warmstart：

Theimportantpointhereisthis.Lettingtheuserspendtoomuchtimelookingatthestartwindowgivesthenampleopportunitytogetboredandmoveontootherthings.AndtakingtoolongingeneralcouldevencausetheApplicationNotRespondingdialogtopop

up.Neitheroftheseareverygoodforuserretention.--真正重要的點(diǎn)是這個(gè)。讓用戶花太長(zhǎng)時(shí)間在啟動(dòng)界面，會(huì)讓他們感到很枯燥，然后轉(zhuǎn)去做別的事情。并且花太長(zhǎng)的時(shí)間在這上面，甚至?xí)?dǎo)致應(yīng)用彈出無(wú)響應(yīng)彈窗（NAR）。這些對(duì)于挽留用戶都是沒(méi)有好處的。

Sofromthetechnicalside,thewholeprocessworkssomethinglikethis.whentheuserlaunchesyourapp,thesystemdoesabitofworktoloadyourapplicationinformationandcreateauniqueprocessforyourapp.--所以，從技術(shù)方面，全部的進(jìn)程工作情況，就如圖下圖。當(dāng)用戶啟動(dòng)你的app，系統(tǒng)會(huì)做一點(diǎn)小工作，加載你的應(yīng)用信息，給你的app創(chuàng)建一個(gè)獨(dú)立的進(jìn)程。

Fromthere,thesystemwilldisplaythestratingwindowandbasicallyhangoutuntiltheapplicationisupandrunning.--從那以后，系統(tǒng)會(huì)顯示啟動(dòng)界面并且會(huì)持續(xù)到應(yīng)用啟動(dòng)和運(yùn)行。

Meanwhile,theapplicationprocesswillcreatetheapplicationobjectandlaunchthemainthread.--同時(shí)，應(yīng)用進(jìn)程會(huì)創(chuàng)建應(yīng)用對(duì)象，啟動(dòng)主線程。

Thisiswhereyourstartupactivitywillbeinitalized,created,inflated,andfinallydrawn.--主線程完成activity的初始化，創(chuàng)建，膨脹，繪制。

it'sonlyatthispoint,aftertheapplicationhasdrawnitsfirstframe,thatthesystemprocessthengoesandswapsoutthestartwindowfortheapplication.--在這點(diǎn)上，當(dāng)應(yīng)用繪制了首幀之后，系統(tǒng)進(jìn)程會(huì)把啟動(dòng)窗口替換成app的顯示窗口。

Now,tobeclear,themajorityofthatentireprocesshappensprettycleanly.There'snotreallymuchchancethatperformancecangoofftherails.However,therearethreebigareaswherethingscouldbecomeproblematicthatyoushouldkeepaneyeon.--現(xiàn)在很清楚了，大多數(shù)的進(jìn)程產(chǎn)生的很干凈（大概這個(gè)意思吧）。性能出差錯(cuò)的可能性也很小。但是還是有三個(gè)大的方面會(huì)造成問(wèn)題，需要你自己關(guān)注。

Thefirstthingyoushouldreallytakealookatisalltheworkthatgoesintocreatingyouractivityclass.Mostoften,there'slotsofheavyliftingthatoccursduringthisprocess,butheaviesthastobetheinflationoflayoutsandloadingofresourcesthatgoesalongwithit.Thisisnotacheapprocess,andifyourlayoutsaretoocomplexoryou'vegotsomeblockinglogicinthere,thiscancausesomereallybigproblems.--第一件你需要真正關(guān)注的事情就是，所有的工作都會(huì)先創(chuàng)建你的activity類。最經(jīng)常的，大量繁重任務(wù)發(fā)生在這個(gè)進(jìn)程期間。但是最繁重的還是inflation布局和加載資源。這不是一個(gè)廉價(jià)的進(jìn)程，如果你的布局太復(fù)雜，或者是你在這里產(chǎn)生了一些閉鎖邏輯，那就會(huì)造成×××煩。

Onasimilarnote,makesureyoutakealookatapplicationinitialization.Forreallycomplexapps,theinitializationoftheappobjectoftenbecomesajunkdrawerforlotsofglobalclassesthatmightbeusedbetweenactivities.Sotheretendstobelotsofworkherethatcouldbedeferredtolatertimesorperhapslodedinalazy-loadfashion.--同樣的，確定你關(guān)注了應(yīng)用的初始化，對(duì)于復(fù)雜的app，app對(duì)象的初始化經(jīng)常會(huì)成為一個(gè)大量全局類的一個(gè)垃圾抽屜，可能會(huì)被用在活動(dòng)中（翻譯的越來(lái)越不行了）。所以這里會(huì)有很多工作可能會(huì)被推遲，或者是在lazy-load模式下加載。

Nowthere'slotsofapplicationsouttherewhichprovidecustomstartwindows.Thisiseitherdonetohelpbrandtheapplicationortomakeaslowloadlooklikeacustom-brandedapplication.Nowifyou'redoingthistohidebadloadtimes,obcviously,youshouldfixthatfirst.Butifyou'redoingitforbranding,thenyouneedtobeawarethatthere'sarightandawrongwaytosetthisup,sothatitdoes'ntinfluencetheuserperceptiontoonegatively.--現(xiàn)在，很多的應(yīng)用都會(huì)提供啟動(dòng)窗口?；蛘邘椭故緫?yīng)用品牌，或者降慢應(yīng)用加載。既然你做這個(gè)就是為了隱藏不好的加載時(shí)間，那么你就應(yīng)該修復(fù)他。但是如果你設(shè)置品牌，那你就應(yīng)該注意到設(shè)置這個(gè)的正確和錯(cuò)誤的方式。以便不會(huì)讓用戶感覺(jué)到太消極。

Butbeforeyourunoffintotheweedsandtrytofixthesetypesofcommonpatterns,youneedtositdownandfigureoutifyouhaveaprobleminthefirstplace.Thankfully,Androidhasafewtoolstohelp.--在解決問(wèn)題之前，如果你在第一個(gè)位置有問(wèn)題，你需要坐下來(lái)，找出它。感謝android有這些工具來(lái)幫助我們。

Firstlyisdisplaytime.ForreleasesafterKitKat,Logcatwillincludeanoutputlinewhichdisplaystheamountoftimebetweenwhentheprocesswaslaunchedandtheactivityfinallydrawntothescreen.Thiscanbehelpful,becauseitgivesyouageneralideahowlongit

takestooccurforyourapplication.--首先是顯示時(shí)間。在KitKat（Android4.4）版本之后，日志將會(huì)包含輸出行，它將顯示在從程序啟動(dòng)到activity最后繪制在屏幕這段總的時(shí)間。這是很有幫助的，對(duì)于你的應(yīng)用啟動(dòng)的時(shí)間，他會(huì)給出一個(gè)大體的建議。

oh,bytheway,notifyouwanttoseethisvalueinisdeofAndroidStudio,youneedtoturnofffiltersfortheLogcatoutput.

Sokeepthatinmind.--噢，記住，如果你不想在AndroidStudio看到這些值，你需要在日志輸出上關(guān)掉過(guò)濾功能。

SecondlyisreportFullyDrawnfunction.Thedisplayedmetricthat'srepotedinLogcatisusefulformostsituationswhereyou'dliketotrackdownthetimeittakestogofromapplicationstarttofirstviseble.Howere,inmodernapplicationdevelopment,there'softenagreatdealoflazyloading-thatis,ratherthanblockingtheinitialdrawingofthewindow,asynchronouslyloadingresourcesandviewsinthebackgroundandupdatingtheviewhierachyaccordingly.Theresultisthatwhiletheinitialactivitymaybevisible,itmaynotyetbefullyloadedwithrespecttoresources,whichcouldbeconsideredaseparatemetrictousewhenevaluatinglaunchtimeperformance.--其次是reportFullyDrawn方法：我們通常來(lái)說(shuō)會(huì)使用異步懶加載的方式來(lái)提升程序畫面的顯示速度，這通常會(huì)導(dǎo)致的一個(gè)問(wèn)題是，程序畫面已經(jīng)顯示，可是內(nèi)容卻還在加載中。為了衡量這些異步加載資源所耗費(fèi)的時(shí)間，我們可以在異步加載完畢之后調(diào)用activity.reportFullyDrawn()方法來(lái)告訴系統(tǒng)此時(shí)的狀態(tài)，以便獲取整個(gè)加載的耗時(shí)。

Toaddressthisconcern,youcanmanuallycalltheactivity.reportFullyDrawnfunctiontoletthesystemknowthatyouractivityisfinishedwithitslazyloading.

Thirdismethodtracing.Whiledisplaytimean