如何正確復制NSMutableArray？

Question

我想用以下代碼復制NSMutableArray：

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

但是當我嘗試在這個新數組中設置一個對象時出現錯誤：

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

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

我也嘗試過：

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

我的SectionArray類：

@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 {
    ...
}

@結束

Answer 1

如果我正確地看到它，則sections是可變數組，但是其元素

[sections objectAtIndex:intSection]

是不可變的數組 ，因此在

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

原因是您將項目復制到此處（ copyItems:YES ）：

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

因此，即使itemsCopy是可變數組的數組，這些元素的副本也是不可變的。

補充：對於嵌套數組的“嵌套可變副本”，可以按以下步驟進行：

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];
}