Optionals yog nyob rau hauv lub hauv paus ntawm Swift thiab muaj nyob txij li thawj version ntawm Swift. Kev xaiv tus nqi tso cai rau peb sau cov lej huv nrog tib lub sijhawm saib xyuas cov txiaj ntsig tsis tau. Yog tias koj tshiab rau Swift koj yuav tsum tau siv rau cov syntax ntawm kev ntxiv cov lus nug rau cov khoom.
Swift xaiv xaiv dab tsi?
Ib qho kev xaiv hauv Swift yog qhov tseem ceeb ib qho tsis tu ncua lossis hloov pauv uas tuaj yeem tuav tus nqi LOSSIS tsis muaj nqi. Tus nqi tuaj yeem lossis tsis tuaj yeem yog nil. Nws yog denoted los ntawm append ib "?" tom qab hom tshaj tawm.
Cov teeb meem dab tsi ua qhov kev xaiv daws tau Swift?
Optionals yog Swift txoj kev daws teeb meem teeb meem ntawm kev sawv cev ntawm tus nqi thiab qhov tsis muaj nqi. Ib qho kev xaiv tau tso cai los tuav tus nqi lossis nil. Xav txog ib qho kev xaiv raws li lub thawv: nws yog muaj raws nraim ib qho nqi, los yog khoob. Thaum nws tsis muaj nqi, nws hais tias muaj nil.
Yuav ua li cas xaiv cov kev xaiv hauv Swift?
Kev xaiv hauv Swift yog qhov tseeb ntau dua li qhov cim ntawm qhov kawg ntawm hom, lawv yeej yog an enum. Qhov tseem ceeb, Int? yog tib yam li Optional, thiab nws yog siv ncaj qha nyob rau hauv lub enum. … Koj tuaj yeem teeb tsa lawv manually nrog lub enum, lossis koj tuaj yeem cia tus enum ua nws tus kheej.
Dab tsi yog qhwv thiab tshem tawm hauv Swift?
Wrapping txhais tau tias tus nqi tiag tiag yog khaws cia rau hauv cov qauv txheej txheem txheej txheem. Koj tsis tuaj yeem tau txais tus nqi ntawd (hauvcov ntaub ntawv no "moo") yam tsis muaj unwrapping nws. Nyob rau hauv Swift ntiaj teb no, nws yog ib txwm Christmas, thiab muaj ib txwm muaj tam sim no - los yog tsawg kawg yog variables - mus unwrap. Koj unwrap qhov tseem ceeb los ntawm kev ntxiv cov ntsiab lus exclamation.
