mutate方法发送到不可变对象 [英] mutating method sent to immutable object

问题描述

当我使用这种方法第一次它工作正常，但当我第二次调用它时，我得到错误mutating方法发送到不可变对象。该问题符合addObject命令。

When I use this method first time it works fine, but when I called it second time I get the error "mutating method sent to immutable object". The problem is at line with "addObject" command.

-(IBAction) save: (id) sender{

NSMutableArray *placesT= [[NSUserDefaults standardUserDefaults] objectForKey:@"placesT"];

if (!placesT) {
    placesT=[[[NSMutableArray alloc] init] autorelease];
}

[placesT addObject: [NSString stringWithFormat:@"%@", tagF.text] ];

NSUserDefaults *tUD=[NSUserDefaults standardUserDefaults];
[tUD setObject:placesT forKey:@"placesT"];
[tUD synchronize];

[self dismissModalViewControllerAnimated:YES];

}

推荐答案

由于NSUserDefaults的文档说：从NSUserDefaults返回的值是不可变的，即使你设置了一个可变对象作为值。每当你想更改从NSUserDefaults获取的集合，你必须得到不可变的版本，使一个 mutableCopy ，修改，并再次设置它。

As the documentation for NSUserDefaults says: "Values returned from NSUserDefaults are immutable, even if you set a mutable object as the value." Whenever you want to change a collection you get from NSUserDefaults you have to get the immutable version, make a mutableCopy, modify that, and set it back again.

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