错误无法使用“String”类型的索引为“Dictionary<NSObject, AnyObject>”类型的值下标答案

【问题标题】：Error Cannot subscript a value of type 'Dictionary<NSObject, AnyObject>' with an index of type 'String'错误无法使用“String”类型的索引为“Dictionary<NSObject, AnyObject>”类型的值下标
【发布时间】：2019-09-17 15:38:18
【问题描述】：

有人可以帮助我吗？我只是将我的小项目从 Objective-C 重新编程到 Swift 并得到以下错误：

不能用“字符串”类型的索引为“字典”类型的值下标

eins、zwei、drei 和 vier 是从另一个视图控制器获取数据的字符串。

Objective-C 代码：

@property (strong, nonatomic) IBOutlet UISwitch *bluetoothSwitch;

- (void)viewDidLoad
{
    [super viewDidLoad];

    NSString *SwitchState;
    NSArray *myStrings = [[NSArray alloc] initWithObjects:eins,zwei,drei, vier, nil];
    SwitchState = [myStrings componentsJoinedByString:mad:" | | "];
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSApplicationSupportDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    NSString *path = [documentsDirectory stringByAppendingPathComponent:mad:"store.plist"];

    NSFileManager *fileManager = [NSFileManager defaultManager];

    if (![fileManager fileExistsAtPath: path]) {
        path = [documentsDirectory stringByAppendingPathComponent: [NSString stringWithFormat:mad:"store.plist"] ];
    }

    NSMutableDictionary *savedValue = [[NSMutableDictionary alloc] initWithContentsOfFile: path];
    if ([[savedValue objectForKey:SwitchState] boolValue]) {
        self.bluetoothSwitch.on = [[savedValue objectForKey:SwitchState] boolValue];
    } else {
    }
}

我的 Swift 代码：

var eins = "Test"
var zwei = "Text"
var drei = "Test"
var vier = "Text"
var SwitchState = ""
let myStrings = [eins, zwei, drei, vier]
SwitchState = myStrings.joined(separator: " | | ")
let paths = NSSearchPathForDirectoriesInDomains(.applicationSupportDirectory, .userDomainMask, true)
let documentsDirectory = paths[0]
var path = URL(fileURLWithPath: documentsDirectory).appendingPathComponent("store.plist").absoluteString

let fileManager = FileManager.default

if !fileManager.fileExists(atPath: path) {
    path = URL(fileURLWithPath: documentsDirectory).appendingPathComponent("store.plist").absoluteString
}

var savedValue = NSDictionary(contentsOfFile: path) as Dictionary?
print("Das bekommt viewdid: \(SwitchState)")
if (savedValue?[SwitchState] as? NSNumber)?.boolValue ?? false {
    bluetoothSwitch.isOn = (savedValue?[SwitchState] as? NSNumber)?.boolValue ?? false
} else {
    print("nein")
}

这两行“产生”错误

if (savedValue?[SwitchState] as? NSNumber)?.boolValue ?? false {
    bluetoothSwitch.isOn = (savedValue?[SwitchState] as? NSNumber)?.boolValue ?? false

【问题讨论】：

究竟是哪一行导致了错误？
我更新了帖子

标签： ios objective-c swift plist

【解决方案1】：

请不要尝试将 Objective-C 代码逐字翻译为 Swift。从 Swift 的角度来看，有很多很多不好的做法。

如果有原生对应类，基本上不要在 Swift 中使用 NS... 类。

发生错误是因为从NSDictionary 到Dictionary（未指定Swift 类型）的桥转换结果是Dictionary<NSObject, AnyObject>，它与值类型String 不兼容

这是一个真正的 Swift 版本：

let eins = "Test"
let zwei = "Text"
let drei = "Test"
let vier = "Text"
let myStrings = [eins, zwei, drei, vier]
let switchState = myStrings.joined(separator: " | | ")
let fileManager = FileManager.default
do {
    let applicationSupportDirectory = try fileManager.url(for: .applicationSupportDirectory, in: .userDomainMask, appropriateFor: nil, create: true)
    let storeURL = applicationSupportDirectory.appendingPathComponent("store.plist")

    let data = try Data(contentsOf: storeURL)
    print("Das bekommt viewdid: \(switchState)")
    if let savedDictionary = try PropertyListSerialization.propertyList(from: data, format: nil) as? [String:Any],
        let savedState = savedDictionary[switchState] as? Bool {
        bluetoothSwitch.isOn = savedState
    } else {
        bluetoothSwitch.isOn = false
        print("nein")
    }
} catch { print(error) }

fileExists(atPath 检查是多余的，所以我把它省略了。

【讨论】：