AnyObject to [String：[String：String]]崩溃而没有错误

Question

说明

我正在尝试将AnyObject从[String: AnyObject]转换为[String: [String: String]]，但只是崩溃而没有任何错误。

    //where my dict is the [String: AnyObject]
    if let data = dict["data"]{
        //We enter here
        print(data)
        //Crashes here.. because of conversion
        for (_, item) in data as! [String: [String: String]]{
            //Do stuff here
        }
    }

以下是数据打印：

{
    1 =     {
        col = "#006666";
        date = "2016-09-01";
        desc = "<null>";
        img = "1.png";
        tit = "title here";
        url = "id=1";
    };
    2 =     {
        col = "#006666";
        date = "2016-07-01";
        desc = "<null>";
        img = "2.png";
        tit = "title here";
        url = "id=2";
    };
    3 =     {
        col = "#006666";
        date = "2016-10-01";
        desc = "<null>";
        img = "3.png";
        tit = "title here";
        url = "id=3";
    };
    4 =     {
        col = "#006666";
        date = "2016-06-01";
        desc = "<null>";
        img = "4.png";
        tit = "title here";
        url = "id=4";
    };
}

问题：

为什么我无法将AnyObject转换为[String: [String: String]]甚至[Int: [String: String]]？

编辑：

将其转换为[String: [String: AnyObject]]让我进入循环。然后，当我尝试处理desc时，它崩溃了：

    //In the loop
    if let description = item["desc"]{
       //Should enter here.. but it doesn't...
       if (description.isEqual(NSNull.self)){
          fotmItem.description = ""
       } else {
          //enters here and attempts to convert "<null>" to string and crashes
          fotmItem.description = description as! String
       }
   }

Answer 1

尝试转换[String：[String：String]]，如下所示。

1. AnyObject as [Any: [String: Any]]，如果您不确定dic键的类型（1,2,3等）。
2. AnyObject as [String: [String: Any]]如果您确定键（1,2,3等）是字符串。

因此，只要您不了解字典值数据类型（Int或String或Null等），[String: Any]就会很有用。

例如：

if let data = dict["data"] as? [String: [String: Any]]{

     for (_, item) in data{
             //Do stuff here
     }
}

处理desc的更新：

if let description = item["desc"] as? String, description != "<null>"{

     fotmItem.description = description

}else{

   fotmItem.description = ""
}

注意：语法在Swift 3.0中

Answer 2

您应该将item["desc"]与NSNull()进行比较，而不是NSNull.self。

替换此

if (description.isEqual(NSNull.self)){

与

if (description.isEqual(NSNull())){

另一种方法是尝试将其转换为String

if let description = item["desc"] as? String {
    fotmItem.description = description
} else {
    fotmItem.description = ""
}