我们可以使用 NSMutable 对象作为非 NSMutable 类的成员吗

发布于 2024-11-05 06:21:04 字数 213 浏览 0 评论 0原文

假设我们有一个简单的 NSDictionary 类，它的对象之一可以是 NSMutableDictionary 对象吗？当我们编辑 NSMutableDictionary 对象中的值时，我们只是编辑 NSDictionary 对象的值。既然我们没有编辑 NSDictionary 的对象，那么对于非可变的 NSDictionary 类来说，这应该是一个问题吗？

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野鹿林 2024-11-12 06:21:04

集合类的可变性仅指修改集合作为一个整体的能力，而不是成员的能力。事实上，集合只是由指向它所包含的对象的指针组成；他们的一切都没有改变。将对象放入不可变集合中不会改变对象本身的修改能力。

所以，是的，您可以毫无困难地修改 NSDictionary 内的 NSMutableDictionary。

NSDictionary * myDict;
myDict = [NSDictionary dictionaryWithObject:
            [NSMutableDictionary dictionaryWithObject:@"This is one string"
                                               forKey:@"sampleKey"]
                                     forKey:@"mutableDict"];

NSMutableDictionary * myMutableDict = [myDict objectForKey:@"mutableDict"];

NSLog(@"%@", [myMutableDict objectForKey:@"sampleKey"];
// Prints "This is one string"

[[myDict objectForKey:@"mutableDict"] setObject:@"Not the same as before" 
                                         forKey:@"sampleKey"];

NSLog(@"%@", [myMutableDict objectForKey:@"sampleKey"];    
// Prints "Not the same as before"

对于任何不可变集合中包含的任何对象（允许修改）也是如此：

@interface MyNeatObjectClass : NSObject {
        NSString * neatString;
}

- (id)initWithNeatString:(NSString *)initialString;
- (void)setNeatString:(NSString *)newString;
- (NSString *)neatString;

MyNeatObjectClass * myObj = [[MyNeatObjectClass alloc] 
                                         initWithNeatString:@"Example string"];

NSLog(@"%@", [myObj neatString]);    // Prints "Example string"
NSArray * arr = [NSArray arrayWithObject:myObj];
[myObj release];

// instance of MyNeatObjectClass
[[arr objectAtIndex:0] setNeatString:@"Another string"];
NSLog(@"%@", [[arr objectAtIndex:0] neatString]);     // Prints "Another string"

The mutability of a collection class refers only to the ability to modify the collection as a whole, not the members. The collection in fact just consists of pointers to the objects it contains; nothing about them is changed. Putting an object inside an immutable collection does not change the object's own ability to be modified.

So, yes, you can modify an NSMutableDictionary inside an NSDictionary, without difficulty.

NSDictionary * myDict;
myDict = [NSDictionary dictionaryWithObject:
            [NSMutableDictionary dictionaryWithObject:@"This is one string"
                                               forKey:@"sampleKey"]
                                     forKey:@"mutableDict"];

NSMutableDictionary * myMutableDict = [myDict objectForKey:@"mutableDict"];

NSLog(@"%@", [myMutableDict objectForKey:@"sampleKey"];
// Prints "This is one string"

[[myDict objectForKey:@"mutableDict"] setObject:@"Not the same as before" 
                                         forKey:@"sampleKey"];

NSLog(@"%@", [myMutableDict objectForKey:@"sampleKey"];    
// Prints "Not the same as before"

Likewise for any object (which allows modification) contained inside any immutable collection:

@interface MyNeatObjectClass : NSObject {
        NSString * neatString;
}

- (id)initWithNeatString:(NSString *)initialString;
- (void)setNeatString:(NSString *)newString;
- (NSString *)neatString;

MyNeatObjectClass * myObj = [[MyNeatObjectClass alloc] 
                                         initWithNeatString:@"Example string"];

NSLog(@"%@", [myObj neatString]);    // Prints "Example string"
NSArray * arr = [NSArray arrayWithObject:myObj];
[myObj release];

// instance of MyNeatObjectClass
[[arr objectAtIndex:0] setNeatString:@"Another string"];
NSLog(@"%@", [[arr objectAtIndex:0] neatString]);     // Prints "Another string"

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