无法分配给“AnyObject?!”类型的不可变表达式

Question

我进行了一些搜索，但仍然无法弄清楚如何解决该错误。 基本上我正在从 Json 文件中读取书单，然后对其进行更新。读取部分没问题，但尝试更新时发生错误（“无法分配给类型为‘AnyObject？！’的不可变表达式”）。

var url = NSBundle.mainBundle().URLForResource("Book", withExtension: "json")

var data = NSData(contentsOfURL: url!)

var booklist = try! NSJSONSerialization.JSONObjectWithData(data!, options: []) as! NSMutableArray


for boo in booklist {
            if (boo["name"]  as! String) == "BookB" {
                print (boo["isRead"]) //see Console Output
                boo["isRead"] = "true"  //this gets error "Cannot assign to immutable expression of type ' AnyObject?!'"
            }

Json 文件 Book.json 如下：

[
{"name":"BookA","auth":"AAA","isRead":"false",},
{"name":"BookB","auth":"BBB","isRead":"false",},
{"name":"BookC","auth":"CCC","isRead":"false",},
]

书单有预期值，见控制台输出：

(
        {
        name = BookA;
        auth = AAA;
        isRead = false;
    },
        {
        name = BookB;
        auth = BBB;
        isRead = false; 
    },
       {
        name = BookC;
        auth = CCC;
        isRead = false;
    }
)

对于print (boo["isRead"])，控制台结果为Optional(false)，这是正确的。

Booklist已经是NSMutableArray了，我也试过改成

var booklist = try! NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions.MutableContainers) as! NSMutableArray

但它没有帮助。

也指Swift: Cannot assign to immutable expression of type 'AnyObject?!'，改成下面也报同样的错误：

var mutableObjects = booklist
for var boo in mutableObjects {
            if (boo["name"]  as! String) == "BookB" {
                print (boo["isRead"]) //see Console Output
                boo["isRead"] = "true"  //this gets error "Cannot assign to immutable expression of type ' AnyObject?!'"
            }

在这种情况下，任何人都可以建议如何更新 BookB 的书单中的 isRead。或者更好的方法是更新 Book.json 文件。

Answer 1

在您的情况下，您两次遇到此错误：

1. 在您正确编辑的for 循环中
2. 因为编译器不知道boo 的类型（它只是NSMutableArray 的一个元素）

要解决这个问题，你可以这样写：

for var boo in mutableObjects {
    if var theBoo = boo as? NSMutableDictionary {
        if (theBoo["name"]  as! String) == "BookB" {
            print (theBoo["isRead"]) //see Console Output
            theBoo["isRead"] = "true"  //this gets error "Cannot assign to immutable expression of type ' AnyObject?!'"
        }
    }
}

或者，你给编译器一个关于boo类型的提示：

    guard let theBoos = mutableObjects as? [Dictionary<String, AnyObject>] else {
        return
    }

    for var theBoo in theBoos {
        if (theBoo["name"]  as! String) == "BookB" {
            print (theBoo["isRead"]) //see Console Output
            theBoo["isRead"] = "true"  //this gets error "Cannot assign to immutable expression of type ' AnyObject?!'"
        }
    }