Question

我做了一些搜索，但仍然无法弄清楚如何解决错误。基本上我正在从Json文件中读取书单，然后更新它。读取部分很好但是在尝试更新时会发生错误（“无法分配给'AnyObject？''类型的不可变表达式。）

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",},
]

书目列表中包含预期值，请参阅控制台输出：

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

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

Booklist已经是一个NSMutableArray，我也尝试改为

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

但它没有帮助。

也称为Swift: Cannot assign to immutable expression of type 'AnyObject?!'，更改为以下内容也会出现同样的错误：

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，是否有人可以建议如何更新BookB的booklist中的isRead。或者甚至更好地更新Book.json文件。

谢谢。

Answer 1

在您的情况下，您遇到此错误两次：

for

因为编译器不知道boo的类型（它只是NSMutableArray的一个元素。

要解决此问题，您可以写

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，您为编译器提供有关{/ 1}}

boo

无法分配给'AnyObject？'类型的不可变表达式

1 个答案: