IGListCollectionContext

@protocol IGListCollectionContext <NSObject>

The collection context provides limited access to the collection-related information that section controllers need for operations like sizing, dequeing cells, insterting, deleting, reloading, etc.

  • The size of the collection view. You can use this for sizing cells.

    Declaration

    Objective-C

    @property (readonly, nonatomic) CGSize containerSize;
  • The content insets of the collection view. You can use this for sizing cells.

    Declaration

    Objective-C

    @property (readonly, nonatomic) UIEdgeInsets containerInset;
  • The size of the collection view with content insets applied.

    Declaration

    Objective-C

    @property (readonly, nonatomic) CGSize insetContainerSize;
  • Returns size of the collection view relative to the section controller.

    Declaration

    Objective-C

    - (CGSize)containerSizeForSectionController:
        (nonnull IGListSectionController *)sectionController;

    Parameters

    sectionController

    The section controller requesting this information.

    Return Value

    The size of the collection view minus the given section controller’s insets.

  • Returns the index of the specified cell in the collection relative to the section controller.

    Declaration

    Objective-C

    - (NSInteger)indexForCell:(nonnull UICollectionViewCell *)cell
            sectionController:(nonnull IGListSectionController *)sectionController;

    Parameters

    cell

    An existing cell in the collection.

    sectionController

    The section controller requesting this information.

    Return Value

    The index of the cell or NSNotFound if it does not exist in the collection.

  • Returns the cell in the collection at the specified index for the section controller.

    Warning

    This method may return nil if the cell is offscreen.

    Declaration

    Objective-C

    - (nullable __kindof UICollectionViewCell *)
    cellForItemAtIndex:(NSInteger)index
     sectionController:(nonnull IGListSectionController *)sectionController;

    Parameters

    index

    The index of the desired cell.

    sectionController

    The section controller requesting this information.

    Return Value

    The collection view cell, or nil if not found.

  • Returns the visible cells for the given section controller.

    Declaration

    Objective-C

    - (nonnull NSArray<UICollectionViewCell *> *)visibleCellsForSectionController:
        (nonnull IGListSectionController *)sectionController;

    Parameters

    sectionController

    The section controller requesting this information.

    Return Value

    An array of visible cells, or an empty array if none are found.

  • Returns the visible paths for the given section controller.

    Declaration

    Objective-C

    - (nonnull NSArray<NSIndexPath *> *)visibleIndexPathsForSectionController:
        (nonnull IGListSectionController *)sectionController;

    Parameters

    sectionController

    The section controller requesting this information.

    Return Value

    An array of visible index paths, or an empty array if none are found.

  • Deselects a cell in the collection.

    Declaration

    Objective-C

    - (void)deselectItemAtIndex:(NSInteger)index
              sectionController:(nonnull IGListSectionController *)sectionController
                       animated:(BOOL)animated;

    Parameters

    index

    The index of the item to deselect.

    sectionController

    The section controller requesting this information.

    animated

    Pass YES to animate the change, NO otherwise.

  • Dequeues a cell from the collection view reuse pool.

    Note

    This method uses a string representation of the cell class as the identifier.

    Declaration

    Objective-C

    - (nonnull __kindof UICollectionViewCell *)
    dequeueReusableCellOfClass:(nonnull Class)cellClass
          forSectionController:(nonnull IGListSectionController *)sectionController
                       atIndex:(NSInteger)index;

    Parameters

    cellClass

    The class of the cell you want to dequeue.

    sectionController

    The section controller requesting this information.

    index

    The index of the cell.

    Return Value

    A cell dequeued from the reuse pool or a newly created one.

  • Dequeues a cell from the collection view reuse pool.

    Note

    This method uses a string representation of the cell class as the identifier.

    Declaration

    Objective-C

    - (nonnull __kindof UICollectionViewCell *)
    dequeueReusableCellWithNibName:(nonnull NSString *)nibName
                            bundle:(nullable NSBundle *)bundle
              forSectionController:
                  (nonnull IGListSectionController *)sectionController
                           atIndex:(NSInteger)index;

    Parameters

    nibName

    The name of the nib file.

    bundle

    The bundle in which to search for the nib file. If nil, this method searches the main bundle.

    sectionController

    The section controller requesting this information.

    index

    The index of the cell.

    Return Value

    A cell dequeued from the reuse pool or a newly created one.

  • Dequeues a storyboard prototype cell from the collection view reuse pool.

    Declaration

    Objective-C

    - (nonnull __kindof UICollectionViewCell *)
    dequeueReusableCellFromStoryboardWithIdentifier:(nonnull NSString *)identifier
                               forSectionController:
                                   (nonnull IGListSectionController *)
                                       sectionController
                                            atIndex:(NSInteger)index;

    Parameters

    identifier

    The identifier of the cell prototype in storyboard.

    sectionController

    The section controller requesting this information.

    index

    The index of the cell.

    Return Value

    A cell dequeued from the reuse pool or a newly created one.

  • Dequeues a supplementary view from the collection view reuse pool.

    Note

    This method uses a string representation of the view class as the identifier.

    Declaration

    Objective-C

    - (nonnull __kindof UICollectionReusableView *)
    dequeueReusableSupplementaryViewOfKind:(nonnull NSString *)elementKind
                      forSectionController:
                          (nonnull IGListSectionController *)sectionController
                                     class:(nonnull Class)viewClass
                                   atIndex:(NSInteger)index;

    Parameters

    elementKind

    The kind of supplementary view.

    sectionController

    The section controller requesting this information.

    viewClass

    The class of the supplementary view.

    index

    The index of the supplementary view.

    Return Value

    A supplementary view dequeued from the reuse pool or a newly created one.

  • Dequeues a supplementary view from the collection view reuse pool.

    Declaration

    Objective-C

    - (nonnull __kindof UICollectionReusableView *)
    dequeueReusableSupplementaryViewFromStoryboardOfKind:
        (nonnull NSString *)elementKind
                                          withIdentifier:
                                              (nonnull NSString *)identifier
                                    forSectionController:
                                        (nonnull IGListSectionController *)
                                            sectionController
                                                 atIndex:(NSInteger)index;

    Parameters

    elementKind

    The kind of supplementary view.

    identifier

    The identifier of the supplementary view in storyboard.

    sectionController

    The section controller requesting this information.

    index

    The index of the supplementary view.

    Return Value

    A supplementary view dequeued from the reuse pool or a newly created one.

  • Dequeues a supplementary view from the collection view reuse pool.

    Note

    This method uses a string representation of the view class as the identifier.

    Declaration

    Objective-C

    - (nonnull __kindof UICollectionReusableView *)
    dequeueReusableSupplementaryViewOfKind:(nonnull NSString *)elementKind
                      forSectionController:
                          (nonnull IGListSectionController *)sectionController
                                   nibName:(nonnull NSString *)nibName
                                    bundle:(nullable NSBundle *)bundle
                                   atIndex:(NSInteger)index;

    Parameters

    elementKind

    The kind of supplementary view.

    sectionController

    The section controller requesting this information.

    nibName

    The name of the nib file.

    bundle

    The bundle in which to search for the nib file. If nil, this method searches the main bundle.

    index

    The index of the supplementary view.

    Return Value

    A supplementary view dequeued from the reuse pool or a newly created one.

  • Invalidate the backing UICollectionViewLayout for all items in the section controller.

    Note

    This method can be wrapped in UIView animation APIs to control the duration or perform without animations. This will end up calling -[UICollectionView performBatchUpdates:completion:] internally, so invalidated changes may not be reflected in the cells immediately.

    Declaration

    Objective-C

    - (void)invalidateLayoutForSectionController:
                (nonnull IGListSectionController *)sectionController
                                      completion:
                                          (nullable void (^)(BOOL))completion;

    Parameters

    sectionController

    The section controller that needs invalidating.

    completion

    An optional completion block to execute when the updates are finished.

  • Batches and performs many cell-level updates in a single transaction.

    Note

    You should make state changes that impact the number of items in your section controller within the updates block alongside changes on the context object.

    For example, inside your section controllers, you may want to delete and insert into the data source that backs your section controller. For example:

    [self.collectionContext performBatchItemUpdates:^ (id<IGListBatchContext> batchContext>){
      // perform data source changes inside the update block
      [self.items addObject:newItem];
      [self.items removeObjectAtIndex:0];
    
      NSIndexSet *inserts = [NSIndexSet indexSetWithIndex:[self.items count] - 1];
      [batchContext insertInSectionController:self atIndexes:inserts];
    
      NSIndexSet *deletes = [NSIndexSet indexSetWithIndex:0];
      [batchContext deleteInSectionController:self atIndexes:deletes];
    } completion:nil];
    

    Warning

    You must perform data modifications inside the update block. Updates will not be performed synchronously, so you should make sure that your data source changes only when necessary.

    Declaration

    Objective-C

    - (void)
    performBatchAnimated:(BOOL)animated
                 updates:(nonnull void (^)(id<IGListBatchContext> _Nonnull))updates
              completion:(nullable void (^)(BOOL))completion;

    Parameters

    animated

    A flag indicating if the transition should be animated.

    updates

    A block with a context parameter to make mutations.

    completion

    An optional completion block to execute when the updates are finished.

  • Scrolls to the specified section controller in the list.

    Declaration

    Objective-C

    - (void)scrollToSectionController:
                (nonnull IGListSectionController *)sectionController
                              atIndex:(NSInteger)index
                       scrollPosition:(UICollectionViewScrollPosition)scrollPosition
                             animated:(BOOL)animated;

    Parameters

    sectionController

    The section controller.

    index

    The index of the item in the section controller to which to scroll.

    scrollPosition

    An option that specifies where the item should be positioned when scrolling finishes.

    animated

    A flag indicating if the scrolling should be animated.