Question

以下代码在尝试removeObjectForKey时返回一个异常，并显示以下错误消息“mutating method sent to immutable object”

NSMutableDictionary * storedIpDictionary = (NSMutableDictionary*)[[NSUserDefaults standardUserDefaults] dictionaryForKey:@"dictDeviceIp"];

NSString *key = self.currentDeviceNameText.text;
NSString *ipAddressTemp = [storedIpDictionary objectForKey:key];

[storedIpDictionary removeObjectForKey:key]; <----Crashes here

storedIpDictionary[key] = ipAddressTemp;

不确定是什么问题，可能是因为从NSUserDefaults检索字典。

但是，以下代码无任何问题。

NSMutableDictionary * storedIpDictionary = (NSMutableDictionary*)[[NSUserDefaults standardUserDefaults] dictionaryForKey:@"dictDeviceIp"];
[storedIpDictionary removeAllObjects];

Answer 1

NSUserDefaults返回不可变对象，即使你输入了可变对象。您必须对返回的值调用-mutableCopy以获取可变集合。

Answer 2

你不能仅仅将NSDictionary投射到NSMutableDictinary，而不是投射的方式。

从NSUserDefualts实例本身的removeObjectForKey电话NSUserDefaults移除密钥。

如果您确实因某些其他原因需要字典，那么您必须从mutableCopy获得的字典中创建dictionaryForKey。

Answer 3

这是最终有效的代码，我使用了上面其他人提供的一些细节，但没有一个完全解释过。

- (void)cleanDictionary
{
    NSMutableDictionary * storedIpDictionary = [[[NSUserDefaults standardUserDefaults] objectForKey: @"dictDeviceIp"] mutableCopy];

    [[NSUserDefaults standardUserDefaults] removeObjectForKey:@"dictDeviceIp"];

    NSString *oldKey = self.currentDeviceNameText.text;
    NSString *newKey = self.deviceNameChangeText.text;
    NSString *ipAddressTemp = [storedIpDictionary objectForKey:oldKey];

    // Make some change to the structure
    [storedIpDictionary removeObjectForKey:oldKey];  // Remove object
    storedIpDictionary[newKey] = ipAddressTemp;      // Add object with new key

    // Add it the whole thing back into NSUserDefaults
    [[NSUserDefaults standardUserDefaults] setObject:storedIpDictionary forKey:@"dictDeviceIp"];

    // Synchronize to ensure it's saved
    [[NSUserDefaults standardUserDefaults] synchronize];
}

Answer 4

如果您有错误NSMutableDictionary：在Swift中发送到不可变对象的mutating方法，请执行以下步骤：

这是因为你已经为NSMutableArray分配了一个NSUserDefault，当你拿NSUserDefault时它会返回一个NSArray而不是NSMutableArray，所以在这种情况下你必须使用NSMutableArray辅助。

参见Swift：

var Products:NSMutableArray = NSMutableArray()


override func viewDidAppear(animated: Bool) {

    if let Produtos = NSUserDefaults.standardUserDefaults().valueForKey("Produtos") {
        Products = Produtos as! NSMutableArray
    }
}

func InsertProducts(productCode:String){
     //COPY Products Atual for auxMutable
     var auxMutable = Products.mutableCopy()

        //Add object in auxMutable
        auxMutable.addObjectsFromArray([productCode])

        //in line back data to Array Products and make cast to NSMutableArray
        Products = auxMutable as! NSMutableArray

        //Refresh Data of NSUserDefaults
        NSUserDefaults.standardUserDefaults().setObject(Products, forKey: "Produtos")
}


@IBAction func Bt_New_Product(sender: AnyObject) {
     var ProductName:String = TXT_NameProduct.text

     InsertProducts(ProductName)
}

这项工作对我来说!!!

Answer 5

我发现了同样的问题，发现解决方案希望它能帮到某个人。

arrayOfferId = defaults.objectForKey("offerId")?.mutableCopy() as! NSMutableArray

NSUserDefaults返回不可变对象，即使你输入了可变对象。您必须在返回的值上调用-mutableCopy以获取可变集合。所以当你从NSUserDefault获得价值时，请使用mutableCopy（）

Answer 6

[NSUserDefaults dictionaryForKey]返回一个不可变的字典（NSDictionary），你不能通过将它强制转换为NSMutableDictionary来强制它变异。

相反，您必须使用mutableCopy创建可变字典，覆盖该元素，然后将字典重新分配回NSUserDefaults：

NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults];
NSMutableDictionary *storedIpDictionary = [[userDefaults dictionaryForKey:@"dictDeviceIp"] mutableCopy];

NSString *key = self.currentDeviceNameText.text;
NSString *ipAddressTemp = [storedIpDictionary objectForKey:key];

// Don't need this line
//[storedIpDictionary removeObjectForKey:key];

storedIpDictionary[key] = ipAddressTemp;
[userDefaults setObject:storedIpDictionary
                 forKey:@"dictDeviceIp"];

NSMutableDictionary：发送到不可变对象的变异方法

6 个答案: