在解析swift中的Json时,无法将'NSNull'类型的值转换为'NSString'

Question

我有以下课程

class BannerResponse : NSObject{

    let  URL                = "Url";
    let  CONTACT_NO         = "ContactNo";
    let  IMAGE              = "Image";
    let  BIG_IMAGE          = "BigImage";
    let  ID                 = "Id";
    let  TITLE              = "Title";
    let  NO_VIEW            = "NoView";
    let  START_DATE         = "StartDate";
    let  END_DATE           = "EndDate";


    var url:String;
    var contactNo:String;
    var image:String;
    var bigImage:String;
    var title:String;
    var id:Int;
    var noView:Int;
    var startDate:String;
    var endDate:String;

    init(data : NSDictionary){

        url         = data[URL] as! String;
        contactNo   = data[CONTACT_NO] as! String;
        image       = data[IMAGE] as! String;
        bigImage    = data[BIG_IMAGE] as! String;
        title       = data[TITLE] as! String;
        id          = data[ID] as! Int;
        noView      = data[NO_VIEW] as! Int;
        startDate   = data[START_DATE] as! String;
        endDate     = data[END_DATE] as! String;
    }
}

当我运行代码时,我收到以下错误

Could not cast value of type 'NSNull' (0x10a85f378) to 'NSString' (0x109eccb20).

编辑

do {

                            if let json = try NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions.MutableContainers) as? NSDictionary{

                                onSuccess(BannerResponse(data: json))
                            }
                        } catch {

                            onFail()
                        }

Answer 1

你的一个data[SOME_KEY]是类型NSNull而不是String因为你String通过使用!应用程序崩溃强制转换.

你可以做以下两件事之一:

1. 将BannerResponse类的变量更改为可选.而?不是!在init方法中设置值时使用.像这样:

`

var title: String?

init(data: NSDictionary) 
{
    self.title = data[TITLE] as? String
}

要么

2. 在设置方法中的值时使用?而不是设置默认值,只要它是nil或不是预期的类型.这看起来像这样:!initdict[SOME_KEY]

`

if let title = data[TITLE] as? String 
{
    self.title = title
}
else
{
    self.title = "default title"
}

// Shorthand would be: 
// self.title = data[TITLE] as? String ?? "default title"

我想第三件事是确保服务器永远不会发送空值.但这是不切实际的,因为从来没有这样的事情.您应该编写客户端代码,以假设JSON中的每个值都可以为null或意外类型.