ios - 如何用新对象替换给定索引处的 NSMutableArray 中的对象

Question

我有一个 NSMutableArray 对象(保留的，合成的)，它启动得很好，我可以使用 addObject: 方法轻松地向它添加对象。但是如果我想用 NSMutableArray 中的新对象替换某个索引处的对象，这是行不通的。

例如:

A类.h:

@interface ClassA : NSObject {
    NSMutableArray *list;
}

@property (nonatomic, copy, readwrite) NSMutableArray *list;

@end

ClassA.m:

#import "ClassA.h"

@implementation ClassA

@synthesize list;

- (id)init 
{
    [super init];
    NSMutableArray *localList = [[NSMutableArray alloc] init];
    self.list = localList;
    [localList release];
    //Add initial data
    [list addObject:@"Hello "];
    [list addObject:@"World"];
}


// Custom set accessor to ensure the new list is mutable
- (void)setList:(NSMutableArray *)newList 
{
    if (list != newList) 
    {
        [list release];
        list = [newList mutableCopy];
    }
}

-(void)updateTitle:(NSString *)newTitle:(NSString *)theIndex
{
    int i = [theIndex intValue]-1;
    [self.list replaceObjectAtIndex:i withObject:newTitle];
    NSLog((NSString *)[self.list objectAtIndex:i]);  // gives the correct output
}

但是，更改仅在方法内部保持为真。从任何其他方法，

NSLog((NSString *)[self.list objectAtIndex:i]);

给出相同的旧值。

我怎样才能在特定索引处用新对象替换旧对象，以便在任何其他方法中也能注意到更改。

我什至这样修改了方法，但结果是一样的:

-(void)updateTitle:(NSString *)newTitle:(NSString *)theIndex
{
    int i = [theIndex intValue]-1;

    NSMutableArray *localList = [[NSMutableArray alloc] init];
    localList = [localList mutableCopy];
    for(int j = 0; j < [list count]; j++)
    {
        if(j == i)
        {
            [localList addObject:newTitle];
            NSLog(@"j == 1");
            NSLog([NSString stringWithFormat:@"%d", j]);
        }
        else
        {
            [localList addObject:(NSString *)[self.list objectAtIndex:j]];
        }
    }
    [self.list release];
    //self.list = [localList mutableCopy];
    [self setList:localList];
    [localList release];
}

请大家帮忙:)

Answer 1

这就是诀窍:

[myMutableArray replaceObjectAtIndex:index withObject:newObject];