將可選字符串轉換爲Int64

Question

我試圖將可選字符串轉換爲字符串，然後轉換爲Int64。

let number = blog["number"] as! String 
print(Int64(number)) 

問題是「數字」鍵是一個可選的字符串，所以它在去Int64時崩潰。我有幾個方法來刪除可選類型，但都沒有工作。

Answer 1

guard let string = blog["number"] as? String else { 
    /* Not a string, handle error here */ 
    return 
} 

guard let number = Int64(string) else { 
    /* string isn't an Int64, handle error here */ 
    return 
} 

//use number here 

您還可以使用if let做解纏，如果你不想退出你的函數。這不是漂亮，但：

if let string = blog["number"] as? String else { 
    if let let number = Int64(string) { 
     //use number here 
    } 
    else { 
     /* string isn't an Int64, handle error here */ 
    } 
} 
else { 
    /* Not a string, handle error here */ 
} 

Answer 2

作爲替代方案，您可以利用的NSNumberFormatter（具體計算財產longLongValue）從Foundation：

import Foundation 

let dict = ["number": "500"] 

if let str = dict["number"], 
    let num = NSNumberFormatter().numberFromString(str)?.longLongValue { 

    /* 'num' is Int64 representation of 'dict["number"]', and we 
     reach this scope only if it exists and can validly be 
     represented as an Int64 number */ 
}