Dab tsi yog kev xaiv khi Swift?
Dab tsi yog kev xaiv khi Swift?

Video: Dab tsi yog kev xaiv khi Swift?

Video: Dab tsi yog kev xaiv khi Swift?
Video: yog hmoov dab tsi. Zoo Xyooj (cover) 2024, Kaum ib hlis
Anonim

Koj siv xaiv los khi mus xyuas seb cov xaiv tau muaj tus nqi lossis tsis. Yog hais tias nws muaj ib tug nqi, unwrap nws thiab muab tso rau hauv ib ntus tas li los yog txawv txav.

Tsis tas li ntawd kom paub yog, dab tsi yog kev xaiv chaining thiab xaiv kev khi hauv Swift?

Cov txheej txheem ntawm querying, hu rau cov khoom, subscripts thiab cov txheej txheem ntawm ib xaiv tau uas tej zaum yuav yog 'nil' yog txhais raws li xaiv chaining . Kev xaiv chaining rov qab ob qhov tseem ceeb - yog tias xaiv tau muaj 'tus nqi' ces hu rau nws cov khoom muaj feem xyuam, txoj hauv kev thiab cov ntawv sau rov qab muaj nuj nqis.

Tsis tas li ntawd, txhais li cas hauv Swift? Swift version: 5.1. Swift siv cov cim exclamation los qhia ob qho tib si quab yuam unwrapping ntawm kev xaiv thiab meej meej unwrapped optionals.

Ib tug kuj nug, yuav ua li cas kuv unwrap xaiv Swift?

Koj ua tau tshem tawm kev xaiv nyob rau hauv peb-thiab-ib-ib nrab txoj kev: Nrog quab yuam unwrapping , siv yog tias [ xaiv tau ] != nil thiab [ xaiv tau ]! Nrog xaiv tau kev khi, siv yog cia [tsis yog- xaiv tau ] = [ xaiv tau ] {

Dab tsi yog cov ntaub ntawv khi hauv Swift?

Cov ntaub ntawv khi . UI cov ntaub ntawv khi yog software tsim qauv kom yooj yim txhim kho cov ntawv thov GUI. UI cov ntaub ntawv khi khi cov ntsiab lus UI rau ib daim ntawv thov sau qauv. Feem ntau lub moj khaum siv tus qauv Observer raws li hauv qab kev khi tshuab.

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