斯威夫特

Question

將字符串轉換爲日期我有日期字符串下面的代碼格式要在Date 改變，但我越來越nil

let addedDate = "Tue, 25 May 2010 12:53:58 +0000" 
let formatter = DateFormatter() 
formatter.dateFormat = "dd MM YYYY" 
let date1 = formatter.date(from: addedDate) 
print("DATE \(date1)") 

Answer 1

日期格式必須是對於您要轉換的字符串，而不是您想要的格式

所以

formatter.dateFormat = "dd MM YYYY" 

應該

formatter.dateFormat = "E, d MMM yyyy HH:mm:ss Z" 

Answer 2

你有你的字符串（addedDateString）轉換爲日期？ （addedDate），那麼你可以使用你想要的格式將它轉換爲一個String（dateString）。請注意：從String到Date的轉換失敗時，addedDate爲零。

import UIKit 

let addedDateString = "Tue, 25 May 2010 12:53:58 +0000" 

// Transform addedDateString to Date 
let addedDateFormatter = DateFormatter() 
addedDateFormatter.dateFormat = "E, d MMM yyyy HH:mm:ss Z" 

if let addedDate = addedDateFormatter.date(from: addedDateString) { 

    // Converstion String to Date return a valid Date 
    print ("addedDate", addedDate) 
    let dateFormatter = DateFormatter() 
    dateFormatter.dateFormat = "dd MM YYYY" 
    let dateString = dateFormatter.string(from: addedDate) 
    print("Date: ", dateString) 

} else { 

    // addedDate == nil value when conversion String to Date failed 
    print ("addedDateString not valid") 

} 

您也可以製作一個功能。類似這樣的：

func transformStringDate(_ dateString: String, 
         fromDateFormat: String, 
         toDateFormat: String) -> String? { 

    let initalFormatter = DateFormatter() 
    initalFormatter.dateFormat = fromDateFormat 

    guard let initialDate = initalFormatter.date(from: dateString) else { 
     print ("Error in dateString or in fromDateFormat") 
     return nil 
    } 

    let resultFormatter = DateFormatter() 
    resultFormatter.dateFormat = toDateFormat 

    return resultFormatter.string(from: initialDate) 
} 

print (transformStringDate("Tue, 25 May 2010 12:53:58 +0000", 
          fromDateFormat: "E, d MMM yyyy HH:mm:ss Z", 
          toDateFormat: "dd MM YYYY") ?? "Error")