NSMutableDictionary：发送到不可变对象的变异方法 [英] NSMutableDictionary: mutating method sent to immutable object

问题描述

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

The following code is returning an exception with the following error message "mutating method sent to immutable object" when attempting to removeObjectForKey

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。

Not sure what the issue is, perhaps it is due to retrieving the dictionary from a NSUserDefaults.

但是下面的代码没有任何问题。

However the following code works without any issues.

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

推荐答案

这是最终有效的代码，我用了一些从上面的其他人提供的细节，但没有完全解释。

This is the code that eventually worked, I used some of the details provided from others above, but none had it completely explained.

- (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];
}

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