说我想用NSIndexSet表示一组稀疏的索引(这当然是这样).我可以使用-firstIndex来获得最低的一个,而-lastIndex是最高的,但是在给定其“索引”的情况下,在中间获得单个任意索引的规范方法是什么？文件让我不清楚.

例如.如果我有一个索引设置索引{0,5,8,10,12,28},我想说“给我第四个索引”,我希望得到10(或12我想依赖关于我是否计数第零,但是我们不介意,你知道我的意思).

请注意,我没有在整个索引集中进行“枚举”.在给定的时间点,我只想知道集合中的第n个索引是按数字顺序排列的.

也许我的数据结构是错误的(“set”通常不是为这种有序的访问而设计的),但似乎没有NSIndexArray可以说.

我错过了什么吗？

谢谢！

NSUInteger index = [indexSet firstIndex];

for (NSUInteger i = 0,target = 4; i < target; i++)
  index = [indexSet indexGreaterThanIndex:index];

那应该给你第四个索引.如果需要,您甚至可以将方法添加为类别方法：

- (NSUInteger)indexAtIndex:(NSUInteger)anIndex
{
    if (anIndex >= [self count])
      return NSNotFound;

    NSUInteger index = [indexSet firstIndex];
    for (NSUInteger i = 0; i < anIndex; i++)
      index = [self indexGreaterThanIndex:index];
    return index;
}

但是,正如你所说,这可能不是最好的数据结构使用,所以在考虑这样的事情之前,请考虑更多.

单元的标识符是photoCell,类是JLTPhotoCell.

- (void)viewDidLoad
        {
            [super viewDidLoad];
            _thumbNails = [[NSArray alloc]init]; // its declared,don't worry about this
            _thumbNails = [[LADataModelController getSingleton] getAllSignatures];

            UICollectionViewFlowLayout *layout = [[UICollectionViewFlowLayout alloc] init];
            [layout setItemSize:( CGSizeMake(50,50))];
            [_collectionView setCollectionViewLayout:layout];
            self.collectionView.delegate = self;
            self.collectionView.dataSource = self;
            [_collectionView registerClass:[JLTPhotoCell class] forCellWithReuseIdentifier:@"photoCell"];
            [self.view addSubview:self.collectionView];
            self.collectionView.allowsSelection = true;
    }

- (NSInteger)collectionView:(UICollectionView *)view numberOfItemsInSection:(NSInteger)section
{
    NSLog(@"count %i",_thumbNails.count);
    return _thumbNails.count;
}

- (NSInteger)numberOfSectionsInCollectionView: (UICollectionView *)collectionView
{
    return 1;
}

- (UICollectionViewCell *)collectionView:(UICollectionView *)cv cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    if (_thumbNails.count > 0)
    {
        JLTPhotoCell *cell = [cv dequeueReusableCellWithReuseIdentifier:@"photoCell" forIndexPath:indexPath];

        NSData *thumbnailData = ((LASignature*)[_thumbNails objectAtIndex:indexPath.row]).signatureImage;
        UIImage* thumbnailImage = [UIImage imageWithData:thumbnailData];
        [cell setThumbnail:thumbnailImage];
        NSLog(@"image:%@",thumbnailImage);

        if (!_buttonSelect.hidden)
        {
            [cell performSelected:FALSE];
        }

        return cell;
    }

    return nil;
}

#pragma mark UICollectionViewDelegate Methods

-(void) collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath
{
    _lastSelectedSign = [_thumbNails objectAtIndex:indexPath.row];

    if (!self.buttonSelect.hidden)
    {
        JLTPhotoCell *cell = (JLTPhotoCell *)[_collectionView cellForItemAtIndexPath:indexPath];
        cell.selected = FALSE;

    }
    else
    {
        [_selectedImages addobject:[_thumbNails objectAtIndex:indexPath.row]];
        JLTPhotoCell *cell = (JLTPhotoCell *)[_collectionView cellForItemAtIndexPath:indexPath];
        [cell performSelected:TRUE];
      //  _buttonDelete.enabled = _selectedImages.count > 0;
    }

}

-(void) collectionView:(UICollectionView *)collectionView diddeselectItemAtIndexPath:(NSIndexPath *)indexPath
{
    [_selectedImages removeObject:[_thumbNails objectAtIndex:indexPath.row]];

    JLTPhotoCell *cell = (JLTPhotoCell *)[_collectionView cellForItemAtIndexPath:indexPath];
    [cell performSelected:FALSE];
    _buttonDelete.enabled = _selectedImages.count > 0;

}

#pragma mark - UICollectionViewDelegateFlowLayout
-(CGSize) collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeforItemAtIndexPath:(NSIndexPath *)indexPath
{
   return  CGSizeMake(50,50) ;
}

-(UIEdgeInsets) collectionView:(UICollectionView *)collectionView layout:(UICollectionViewFlowLayout *)collectionViewLayout insetForSectionAtIndex:(NSInteger)section
{
    collectionViewLayout.minimumInteritemSpacing=1;
    collectionViewLayout.minimumLinespacing =2;
    return UIEdgeInsetsMake(1,1,1);
}

jltPhotoCell Class
-(void) setThumbnail:(UIImage *) thumbnail
{
    [self setThumbnail:thumbnail andWithSize:(CGSizeMake(50,50))];
}

-(void) setThumbnail:(UIImage *) thumbnail andWithSize:(CGSize) size
{
    UIImageView *thumbImageView = [[UIImageView alloc] initWithImage:thumbnail];
    thumbImageView.frame = CGRectMake(0,size.width,size.height);
    thumbImageView.userInteractionEnabled = YES;
    [self.contentView addSubview:thumbImageView];
}

-(void) performSelected:(bool)selected
{
    if (selected)
    {
        UIImageView *deleteImageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"delete"]];
        deleteImageView.frame = CGRectMake(self.contentView.frame.size.width - 35,3,32,32);
        deleteImageView.tag = 123;
        [self.contentView addSubview:deleteImageView];
    }
    else
    {
        UIView *v = [self.contentView viewWithTag:123];
        v.hidden = YES;
        [self.contentView bringSubviewToFront:v];
        [v removeFromSuperview];
    }
}

任何建议将不胜感激.谢谢.

但是,在数据源工作之后分配代理.

我变了：

self.collectionView.delegate = self;
self.collectionView.dataSource = self;

有：

self.collectionView.dataSource = self;
self.collectionView.delegate = self;