如何正确复制NSMutableArray？

Question

我想用以下代码复制NSMutableArray：

SectionArray *newSectionArray = [[SectionArray alloc] init];    
NSMutableArray *itemsCopy = [self.sections mutableCopy];
newSectionArray.sections = [[NSMutableArray alloc] initWithArray:itemsCopy copyItems:YES];

但是当我尝试在这个新数组中设置一个对象时出现错误：

[[self.sections objectAtIndex:intSection] replaceObjectAtIndex:intRow withObject:object];

[__NSArrayI replaceObjectAtIndex:withObject:]: unrecognized selector sent to instance 0x7191720

我也尝试过：

SectionArray *newSectionArray = [[SectionArray alloc] init];    
newSectionArray.sections = [[[NSMutableArray alloc] initWithArray:itemsCopy copyItems:YES] mutableCopy];

我的SectionArray类：

@implementation SectionArray

@synthesize sections;
@synthesize value;

- initWithSectionsForWayWithX:(int)intSections andY:(int)intRow {
    NSUInteger i;
    NSUInteger j;

    if ((self = [self init])) {
        sections = [[NSMutableArray alloc] initWithCapacity:intSections];
        for (i=0; i < intSections; i++) {
            NSMutableArray *a = [NSMutableArray arrayWithCapacity:intRow];
            for (j=0; j < intRow; j++) {
                Node * node = [[Node alloc] initNodeWithX:i  andY:j andValeur:0];
                [a insertObject:node atIndex:j];
            }
            [sections addObject:a];
        }
    }
    return self;
}

- (void)setObjectForNode:(Node *)object andX:(int)intSection andY:(int)intRow {

    [[sections objectAtIndex:intSection] replaceObjectAtIndex:intRow withObject:object];
}

- (SectionArray *) copy {
    ...
}

@结束

Answer 1

如果我正确地看到它，则sections是可变数组，但是其元素

[sections objectAtIndex:intSection]

是不可变的数组 ，因此在

[[sections objectAtIndex:intSection] replaceObjectAtIndex:intRow withObject:object];

原因是您将项目复制到此处（ copyItems:YES ）：

newSectionArray.sections = [[NSMutableArray alloc] initWithArray:itemsCopy copyItems:YES];

因此，即使itemsCopy是可变数组的数组，这些元素的副本也是不可变的。

补充：对于嵌套数组的“嵌套可变副本”，可以按以下步骤进行：

SectionArray *newSectionArray = [[SectionArray alloc] init];
newSectionArray.sections = [[NSMutableArray alloc] init];
for (NSUInteger i=0; i < [sections count]; i++) {
    NSMutableArray *a = [[sections objectAtIndex:i] mutableCopy];
    [newSectionArray.sections addObject:a];
}