ios - Swift - EXC_BAD_ACCESS 尝试将 dict 值读取为 Int 时

Question

假设我有一个定义如下的字典:

let path = NSBundle.mainBundle().pathForResource("books", ofType: "plist")
let dict = NSDictionary(contentsOfFile: path)
let books = dict.objectForKey("Books") as [[String:AnyObject]] 
let rnd = Int(arc4random_uniform((UInt32(books.count))))
let bookData = books[rnd]

为什么会这样？

let author = bookData["author"]! as String

但这会导致崩溃:

let chapterNum = bookData["chapterNum"]! as Int //should be 5, for example

bookData 的日志给出了这个:

bookData: [content: whatever, author: John Doe, tags: (
    tagA,
    tagB
), chapterNum: 5]

Answer 1

bookData["chapterNum"] 可能是 String 而不是 Int

尝试

let chapterNum = dict["chapterNum"] as? Int

如果类型不是你期望的，你将得到 nil

如果您从字典中获取字符串，您可以先获取该字符串并尝试将其转换为 Int

var chapterNum = 0
if let chapterNumString = dict["chapterNum"] as? String {
    if let chapterNumInt = chapterNumString.toInt()? {
        chapterNum = chapterNumInt
    }
}

如果您不想稍后在该函数调用中处理可选的 int 值