如何在swift中安全地解開零值？

Question

我是相當新的迅速和我想了解如何處理零瓦爾...

我有兩個字典：

var currencyname: NSDictionary = [ 
     "CNY": "Chinese Yuan", 
     "PLN": "Polish Zloty" 
     "EUR": "Euro" 
] 

var rawrates NSDictionary = [ 
     "CNY": "1.34", 
     "PLN": "1.456" 
] 

我使用的元組的字典將它們組合起來：

var combinedDictionary:[String:(name:String,rate:String)] = [:] 

for key in currencyname.keys.array { 
    combinedDictionary[key] = (currencyname[key]!,rawrates[key]!) 
} 

但是我得到了found nil while unwrapping an Optional value錯誤，因爲在currencyname字典不匹配的rawrate詞典中的任何密鑰的密鑰EUR。

我明白，我會以某種方式檢查鑰匙字典都存在使用let if結合之前？但是我對語法感到困惑......我也嘗試過使用可選值而沒有成功。

所以我的問題是我怎麼能結合這兩個字典，並離開EUR combinedDictionary因爲在rawrate字典中沒有匹配的關鍵？

謝謝您的幫助！

Answer 1

我認爲你是什麼這樣的事情後：

let currencyname = [ 
     "CNY": "Chinese Yuan", 
     "PLN": "Polish Zloty", 
     "EUR": "Euro" 
    ] 

    let rawrates = [ 
     "CNY": "1.34", 
     "PLN": "1.456" 
    ] 

    var combinedDictionary = [String:(name:String,rate:String)]() 
    for key in currencyname.keys { 
     if let val1 = currencyname[key], val2 = rawrates[key] { 
      combinedDictionary[key] = (val1,val2) 
     } 
    } 

但它是一個有點硬不更清晰的問題陳述是肯定的。這不是我會建議的。這在我看來是一個更好的結果：

let currencyname = [ 
    "CNY": "Chinese Yuan", 
    "PLN": "Polish Zloty", 
    "EUR": "Euro" 
] 

let rawrates = [ 
    "CNY": "1.34", 
    "PLN": "1.456" 
] 

struct Currency { 
    let name : String 
    let rate : String 
} 

var combinedDictionary = [String:Currency]() 
for key in currencyname.keys { 
    if let val1 = currencyname[key], val2 = rawrates[key] { 
     combinedDictionary[key] = Currency(name:val1, rate:val2) 
    } 
}