Downcast from'String ?!'以'字符串'僅解開可選項;你的意思是使用'!!'嗎？在迅速

Question

源代碼是波紋管

let json = try NSJSONSerialization.JSONObjectWithData(data!, options: .AllowFragments) 
         if let blogs = json["profile_image_url"] as? String { 

          userImage = blogs//json["profile_image_url"] as! String 
          print("USER IMAGE:\(userImage)") 

我如何解決這個問題

Answer 1

你想測試和解開任何Optional然後再使用它們。這包括像as?。如果可以避免它，則不應使用強制解包或明確解包Optional（標記爲!），因爲它們會導致意外的運行時崩潰。

import Foundation 

// create test data 
let testJson = ["profile_image_url": "http://some.site.com/"] 
var data: NSData? 

// convert to NSData as JSON 
do { 
    data = try NSJSONSerialization.dataWithJSONObject(testJson, options: []) 
} catch let error as NSError { 
    print(error) 
} 

// decode NSData 
do { 
    // test and unwrap data 
    if let data = data { 
    let json = try NSJSONSerialization.JSONObjectWithData(data, options: .AllowFragments) 
    // test and unwrap cast to String 
    if let userImage = json["profile_image_url"] as? String { 
     print("USER IMAGE:\(userImage)") 
    } 
    } 
} catch let error as NSError { 
    print(error) 
}