NSCollectionView的collectionView:itemForRepresentedObjectAtIndexPath:方法从未被调用

Question

我已经习惯了iOS的UICollectionView，并且尝试在OSX上设置一个NSCollectionView，而不使用任何故事板(大多数教程使用.xibs，所以它们略有不同)。API看起来类似，但我无法获得集合视图来调用dataSource的collectionView:itemForRepresentedObjectAtIndexPath:方法。

我已经将我的原始代码简化到了我认为调用此dataSource方法所需的集合视图的最小值：

@import Cocoa;

static NSString * const kCollectionViewControllerItemID = @"ItemID";

@interface CollectionViewItem : NSCollectionViewItem
@end

@implementation CollectionViewItem
@end

@interface CollectionViewController : NSViewController  <NSCollectionViewDelegate, NSCollectionViewDataSource>

@property (nonatomic, strong) NSCollectionView *collectionView;

@end

@implementation CollectionViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    NSCollectionViewFlowLayout *layout = [[NSCollectionViewFlowLayout alloc] init];
    [layout setItemSize:CGSizeMake(100, 100)];

    _collectionView = [[NSCollectionView alloc] init];
    [_collectionView setTranslatesAutoresizingMaskIntoConstraints:NO];
    [_collectionView setCollectionViewLayout:layout];
    [_collectionView setDataSource:self];
    [_collectionView setDelegate:self];
    [_collectionView registerClass:[CollectionViewItem class] forItemWithIdentifier:kCollectionViewControllerItemID];
    [[self view] addSubview:_collectionView];
    [[self view] addConstraints:@[
                                  [NSLayoutConstraint constraintWithItem:_collectionView attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:[self view] attribute:NSLayoutAttributeTop multiplier:1.0f constant:0],
                                  [NSLayoutConstraint constraintWithItem:_collectionView attribute:NSLayoutAttributeLeading relatedBy:NSLayoutRelationEqual toItem:[self view] attribute:NSLayoutAttributeLeading multiplier:1.0f constant:0],
                                  [NSLayoutConstraint constraintWithItem:[self view] attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:_collectionView attribute:NSLayoutAttributeBottom multiplier:1.0f constant:0],
                                  [NSLayoutConstraint constraintWithItem:[self view] attribute:NSLayoutAttributeTrailing relatedBy:NSLayoutRelationEqual toItem:_collectionView attribute:NSLayoutAttributeTrailing multiplier:1.0f constant:0],
                                  ]];
}

- (NSInteger)collectionView:(NSCollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
    return 1;
}

- (NSCollectionViewItem *)collectionView:(NSCollectionView *)collectionView itemForRepresentedObjectAtIndexPath:(NSIndexPath *)indexPath
{
    //this method is never called
    return [collectionView makeItemWithIdentifier:kCollectionViewControllerItemID forIndexPath:indexPath];
}

@end

这个实现缺少了什么？

编辑:为了便于复制，我在GitHub https://github.com/BradB132/OSXCollectionViewTest上建立了一个示例项目。

Answer 1

因此，您需要将NSCollectionView封装在NSScrollView中：

NSScrollView *scrollView = [[NSScrollView alloc] initWithFrame:NSZeroRect];
_collectionView = [[NSCollectionView alloc] initWithFrame:NSZeroRect];
scrollView.documentView = _collectionView;
[self.view addSubview:scrollView];

现在应该调用collectionView:itemForRepresentedObjectAtIndexPath：。