xcode NSMutableArray 的 NSMutableArray。发送到不可变对象的变异方法

NSMutableArray of NSMutableArrays. Mutating method sent to immutable object

提问by SmartTree

I have NSMutableArrayof NSMutableArrays:

我NSMutableArray的NSMutableArrays：

 NSMutableArray *array = [[NSMutableArray alloc]init];

        for (int i = 0; i < 5; i++)
        {
            NSMutableArray *miniArray = [[NSMutableArray alloc]init];

            for (int k = 0; k < 30; k++)
            {   
                [miniArray addObject:@"0"];
            }
            [array addObject:miniArray];
        }

Then, when I try to do this:

然后，当我尝试这样做时：

 [[array objectAtIndex:packIndex]replaceObjectAtIndex:index withObject:@"1"];

it crashes with: [__NSCFArray replaceObjectAtIndex:withObject:]: mutating method sent to immutable object'

它崩溃了： [__NSCFArray replaceObjectAtIndex:withObject:]: mutating method sent to immutable object'

Why ? How to fix ? Thanks !

为什么 ？怎么修 ？谢谢 ！

UPD: I save this array in NSUserDefaults:

UPD：我将此数组保存在NSUserDefaults：

[defaults setObject:array forKey:@"mainArray"];

Then, I read it in the other class:

然后，我在另一堂课上读到：

array = [[NSMutableArray alloc]initWithArray:[[NSUserDefaults standardUserDefaults] objectForKey:@"mainArray"]];

Also, I must to mention that sometimes the code runs well and it changes "0" to "1". But it also crashes sometimes. So I cant see the logic, why it works fine or why it crashes sometimes.

另外，我必须提到，有时代码运行良好，它会将“0”更改为“1”。但它有时也会崩溃。所以我看不到逻辑，为什么它工作正常或为什么有时会崩溃。

回答by Lance

The problem is that when you read the array out of NSUserDefaults, the mini-arrays are not automatically NSMutableArrays.

问题是当您从 NSUserDefaults 中读取数组时，小数组不会自动成为 NSMutableArrays。

Try this:

尝试这个：

array = [[NSMutableArray alloc]initWithArray:[[NSUserDefaults standardUserDefaults] objectForKey:@"mainArray"]];
for(int i = 0; i < array.count; i++) {
    NSArray * tempArray = array[i];
    array[i] = [tempArray mutableCopy];
}

Edit: Best Coder's answer explains why this is. Objects stored in NSUserDefaults are stored as immutable versions, basically NSUserDefaults is a plist and there is no flag marking an array as mutable/immutable so when you read them back out, they are assumed to be immutable.

编辑：Best Coder 的回答解释了为什么会这样。存储在 NSUserDefaults 中的对象存储为不可变版本，基本上 NSUserDefaults 是一个 plist 并且没有将数组标记为可变/不可变的标志，因此当您将它们读回时，它们被假定为不可变的。

回答by aks.knit1108

Values returned from NSUserDefaults are immutable, even if you set a mutable object as the value. For example, if you set a mutable string as the value for "MyStringDefault", the string you later retrieve using stringForKey: will be immutable.

从 NSUserDefaults 返回的值是不可变的，即使您将可变对象设置为值。例如，如果您将可变字符串设置为“MyStringDefault”的值，那么您稍后使用 stringForKey: 检索的字符串将是不可变的。

Instead, make a mutableCopy of the array you retrieve from NSUserDefaults, add your object, then set your new array back in.

相反，制作从 NSUserDefaults 检索到的数组的 mutableCopy，添加对象，然后重新设置新数组。

see this link: http://developer.apple.com/library/mac/#documentation/Cocoa/Reference/Foundation/Classes/NSUserDefaults_Class/Reference/Reference.html

请参阅此链接：http: //developer.apple.com/library/mac/#documentation/Cocoa/Reference/Foundation/Classes/NSUserDefaults_Class/Reference/Reference.html

回答by Chris C

Try using more verbose code:

尝试使用更详细的代码：

NSMutableArray *tempArray = [array objectAtIndex:packIndex];
[tempArray replaceObjectAtIndex:index withObject:@"1"];