Swift Dictionary 已填满但仍为空

Question

我已经解决一个问题太久了，我真的不明白为什么会发生这种情况。我在网上搜索了解决方案，我已经尝试了每一个，但我仍然遇到这个问题。我在 Swift 中初始化了一个字典，然后向它添加了一些值，但是在我添加了键/值之后，字典是空的（在调试模式下检查），稍后在尝试从中读取时在代码中也是 nil .这是我当前的代码：

我首先得到要在其中添加字典的 plist：

var path = NSBundle.mainBundle().pathForResource("Questions", ofType: "plist")
var dict = NSDictionary(contentsOfFile: path!)!
var questionsArr = dict.objectForKey("Math") as NSArray
var questionsMutableArray:NSMutableArray = questionsArr.mutableCopy() as NSMutableArray

然后我创建并向我的字典添加值

//I have also tried with this and got the same result: var newDict = Dictionary<String, String>()
var newDict = [String: String]()
newDict["Question"] = "What is 1+1"
newDict["A"] = "One"
newDict["B"] = "Two"
newDict["C"] = "Three"

这里的调试模式下，newDict 似乎是空的。 然后我将字典写入我的 plist：

questionsMutableArray.addObject(newDict)
questionsMutableArray.writeToFile(path!, atomically: true)

稍后在代码中，我得到了这样的 plist（在我没有添加 newDict 之前它工作过：

var path = NSBundle.mainBundle().pathForResource("Questions", ofType: "plist")
var dict = NSDictionary(contentsOfFile: path!)!

在最后一行 (NSDictinoary(contentsOfFile:path!)！我收到此错误：

fatal error: unexpectedly found nil while unwrapping an Optional value

有人知道为什么会这样吗？ 帮助将不胜感激！

EDIT4)中的解决方案

1. I'm getting an array of dictionaries from my plist (Questions).
2. I add a new dictionary to my array of dictionaries.
3. I write/save it to the plist.
4. I get the array from the plist again and investigate the content of it.
5. The new dictionary I just added is not there.

这是代码：

1) questionsArr 为空

var bundlepath:NSString = NSBundle.mainBundle().pathForResource("Questions", ofType: "plist")!

        var dict = NSMutableDictionary(contentsOfFile: bundlepath)!
        var questionsArr = dict.objectForKey("Math") as NSArray
        var questionsMutableArray:NSMutableArray = questionsArr.mutableCopy() as NSMutableArray

2) questionsMutableArray 为空，现在包含新问题。

var newDict = [String: String]()
    newDict["QuestionTitle"] = "What is 1+1?"
    newDict["A"] = "One"
    newDict["B"] = "Two"
    newDict["C"] = "Three"

let documentsPath = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true)[0] as NSString
var path:NSString = documentsPath.stringByAppendingPathComponent("Questions.plist");

questionsMutableArray.addObject(newDict)
dict["Math"] = questionsMutableArray

3)

let didItSave = dict.writeToFile(path, atomically: true)

4) questionsArr 仍然为空。如果我使用 'path' 而不是 'bundlepath' 就可以了！

dict = NSMutableDictionary(contentsOfFile: bundlepath)! //<- I USED 'path' INSTEAD OF 'bundlepath' and now it works!
    questionsArr = dict.objectForKey("Math") as NSArray

Answer 1

您正在尝试编写 iOS Bundle。 iOS Bundle 是只读的，不能写。

我建议你写在 Document 目录 试试这个方法

 var bundlepath:NSString= NSBundle.mainBundle().pathForResource("Questions", ofType: "plist")

    var dict = NSDictionary(contentsOfFile: bundlepath)!
    var questionsArr = dict.objectForKey("Math") as NSArray
    var questionsMutableArray:NSMutableArray = questionsArr.mutableCopy() as NSMutableArray


    //I have also tried with this and got the same result: var newDict = Dictionary<String, String>()
    var newDict = [String: String]()
    newDict["Question"] = "What is 1+1"
    newDict["A"] = "One"
    newDict["B"] = "Two"
    newDict["C"] = "Three"

    let documentsPath = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true)[0] as NSString
    var path:NSString = documentsPath.stringByAppendingPathComponent("Questions.plist");



questionsMutableArray.addObject(newDict)

//将数组分配回字典。 dict["Math"]=questionsMutableArray

dict.writeToFile(path!, atomically: true)

    var dictFromDisk = NSDictionary(contentsOfFile: path)!

Answer 2

首先，当您检索 plist 时，将其检索到 NSMutableDictionary

var dict = NSMutableDictionary(contentsOfFile: path!)!

然后，一旦您创建了数组，请将您的字典数学键设置为它。

dict["math"] = questionsMutableArray

然后将字典写回你的路径。可能想看看它是否有效，writeToFile 返回一个布尔值。

let didItSave = dict.writeToFile(path!, atomically: true)

Answer 3

您的 plist 文件是一个字典数组，因此当您检索它时，您必须将其检索为 NSArray，然后将其转换为 Dictionary<String, String> 的数组

let array = NSArray(contentsOfFile: NSBundle.mainBundle().pathForResource("Questions", ofType: "plist")!) as [[String: String]]

然后，您可以使用以下方法访问此数组中的特定字典：

let someDict = array[someIndex]

Answer 4

编辑了我的答案：

您正在使用以下行保存数组

questionsMutableArray.writeToFile(path!, atomically: true)

但随后尝试将其加载为字典。您应该将问题数组设置为字典的“数学”键，然后像这样保存字典本身以使您的读写兼容。

dict["Math"] = questionsMutableArray 
dict.writeToFile(path!, atomically: true)