在自定义UICollectionView中出列时返回了错误的单元格

Question

我正在构建一个带有自定义布局的UICollectionView。

布局为3x4，水平滚动。 我得到了单元格的布局和页面滚动工作得很好。

我的预期结果是这样的：

（见http://www.tinyuploads.com/images/0EVQnT.png ）

但是，当滚动时，似乎错误的单元格正在出列，而我的实际结果是：

（见http://www.tinyuploads.com/images/8lvJId.png ）

此外，当我向后滚动到第一页时，“A”不再处于第一个位置。

我的数据源和委托方法如下所示：

#pragma mark - UIViewController Life Cycle

- (void)viewDidLoad
{
    [super viewDidLoad];

    self.collectionView.backgroundColor = [UIColor colorWithWhite:0.25f alpha:1.0f];
    self.alphabet = [NSMutableArray arrayWithObjects:@"A", @"B", @"C", @"D", @"E", @"F", @"G", @"H", @"I", @"J", @"K", @"L", @"M", @"N", @"O", @"P", @"Q", @"R", @"S", @"T", @"U", @"V", @"X", @"Y", @"Z", nil];
    self.colors = [NSMutableArray arrayWithObjects:[UIColor colorWithRed:(135/255.0) green:(175/255.0) blue:(88/255.0) alpha:1], [UIColor colorWithRed:(65/255.0) green:(124/255.0) blue:(185/255.0) alpha:1], [UIColor colorWithRed:(201/255.0) green:(189/255.0) blue:(64/255.0) alpha:1],  nil];

    [self.collectionView reloadData];
}


#pragma mark - UICollectionView datasource

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

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section{

    return self.alphabet.count;

}

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{

    NSString *title = [self.alphabet objectAtIndex:indexPath.row];
    UIColor *backgroundColor = [self.colors objectAtIndex:indexPath.row % 3];

    CategoryCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:CategoryCellIdentifier forIndexPath:indexPath];

    cell.title.text = title;
    cell.backgroundColor = backgroundColor;
    [cell setNeedsLayout];

    return cell;

}

#pragma mark - UICollectionViewDelegate

- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath{

    NSLog(@"You touched: %d", indexPath.row);
}

我怀疑我应该如何思考各个部分。 如您所见，我只有一个部分包含我的所有项目（字母表的内容）。

任何帮助都非常感谢。

Answer 1

WFrom我可以告诉它看起来子类可能没有正确实现。 下面是使用内置水平流布局的示例，您可以使用它来修改代码。

注意：此示例假定您在故事板中设置了正确的大小，并且您将有3列乘4行。

@interface ViewController ()
@property (nonatomic, strong) NSMutableArray* alphabet;
@property (nonatomic, strong) NSMutableArray* colors;

@end

@implementation ViewController

- (void)viewDidLoad
{
    [super viewDidLoad];

    self.collectionView.backgroundColor = [UIColor colorWithWhite:0.25f alpha:1.0f];
    self.alphabet = [NSMutableArray arrayWithObjects:@"A", @"B", @"C", @"D", @"E", @"F", @"G", @"H", @"I", @"J", @"K", @"L", @"M", @"N", @"O", @"P", @"Q", @"R", @"S", @"T", @"U", @"V", @"W", @"X", @"Y", @"Z", nil];
    self.colors = [NSMutableArray arrayWithObjects:[UIColor colorWithRed:(135/255.0) green:(175/255.0) blue:(88/255.0) alpha:1], [UIColor colorWithRed:(65/255.0) green:(124/255.0) blue:(185/255.0) alpha:1], [UIColor colorWithRed:(201/255.0) green:(189/255.0) blue:(64/255.0) alpha:1],  nil];

    [self.collectionView reloadData];
}
#pragma mark - UICollectionView datasource

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

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section{
    // Full pages
    NSInteger count = self.alphabet.count /12 + (self.alphabet.count % 12 > 0 ? 1 : 0);
    count *= 12;
    return count;
}

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{


    NSInteger row = indexPath.row % 4;
    NSInteger col = indexPath.row / 4;
    NSInteger page = col /3 * 12;
    col = col % 3;
    NSInteger ii = row*3+col + page;

    NSString *title = ii >= self.alphabet.count ? nil : [self.alphabet objectAtIndex:ii];
    UIColor *backgroundColor = [self.colors objectAtIndex:col];

    UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"Cell" forIndexPath:indexPath];
    UILabel* label = (UILabel*)[cell viewWithTag:1]; // label added in storyboard
    label.text = title;
    cell.backgroundColor = backgroundColor;
    [cell setNeedsLayout];
    cell.hidden = title == nil;
    return cell;

}

#pragma mark - UICollectionViewDelegate

- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath{

    NSLog(@"You touched: %d", indexPath.row);
}
@end