iOS-UICollectionViewDelegate&DataSource

UICollectionViewDelegate

@protocol UICollectionViewDelegate 
@optional

// Methods for notification of selection/deselection and highlight/unhighlight events.
// The sequence of calls leading to selection from a user touch is:

//当开始触摸时走以下方法
// (when the touch begins)
// 1. -collectionView:shouldHighlightItemAtIndexPath:
// 2. -collectionView:didHighlightItemAtIndexPath:
//
// (when the touch lifts)

// 3.返回这个UICollectionView是否可以被选择  
// 3. -collectionView:shouldSelectItemAtIndexPath: or -collectionView:shouldDeselectItemAtIndexPath:
// 4. -collectionView:didSelectItemAtIndexPath: or -collectionView:didDeselectItemAtIndexPath:
// 5. -collectionView:didUnhighlightItemAtIndexPath:
- (BOOL)collectionView:(UICollectionView *)collectionView shouldHighlightItemAtIndexPath:(NSIndexPath *)indexPath;
- (void)collectionView:(UICollectionView *)collectionView didHighlightItemAtIndexPath:(NSIndexPath *)indexPath;
- (void)collectionView:(UICollectionView *)collectionView didUnhighlightItemAtIndexPath:(NSIndexPath *)indexPath;
- (BOOL)collectionView:(UICollectionView *)collectionView shouldSelectItemAtIndexPath:(NSIndexPath *)indexPath;
- (BOOL)collectionView:(UICollectionView *)collectionView shouldDeselectItemAtIndexPath:(NSIndexPath *)indexPath; // called when the user taps on an already-selected item in multi-select mode
- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath;
- (void)collectionView:(UICollectionView *)collectionView didDeselectItemAtIndexPath:(NSIndexPath *)indexPath;


//将要绘制cell时
- (void)collectionView:(UICollectionView *)collectionView willDisplayCell:(UICollectionViewCell *)cell forItemAtIndexPath:(NSIndexPath *)indexPath NS_AVAILABLE_IOS(8_0);
//将绘制SupplementaryView时
- (void)collectionView:(UICollectionView *)collectionView willDisplaySupplementaryView:(UICollectionReusableView *)view forElementKind:(NSString *)elementKind atIndexPath:(NSIndexPath *)indexPath NS_AVAILABLE_IOS(8_0);
//结束绘制之后
- (void)collectionView:(UICollectionView *)collectionView didEndDisplayingCell:(UICollectionViewCell *)cell forItemAtIndexPath:(NSIndexPath *)indexPath;
- (void)collectionView:(UICollectionView *)collectionView didEndDisplayingSupplementaryView:(UICollectionReusableView *)view forElementOfKind:(NSString *)elementKind atIndexPath:(NSIndexPath *)indexPath;

// These methods provide support for copy/paste actions on cells.
// All three should be implemented if any are.
//是否显示菜单 
- (BOOL)collectionView:(UICollectionView *)collectionView shouldShowMenuForItemAtIndexPath:(NSIndexPath *)indexPath;
 //菜单中哪些编辑操作可以显示
- (BOOL)collectionView:(UICollectionView *)collectionView canPerformAction:(SEL)action forItemAtIndexPath:(NSIndexPath *)indexPath withSender:(nullable id)sender;
 //对于显示的编辑操作怎么执行
- (void)collectionView:(UICollectionView *)collectionView performAction:(SEL)action forItemAtIndexPath:(NSIndexPath *)indexPath withSender:(nullable id)sender;

// support for custom transition layout
//提供自定义布局过渡
- (nonnull UICollectionViewTransitionLayout *)collectionView:(UICollectionView *)collectionView transitionLayoutForOldLayout:(UICollectionViewLayout *)fromLayout newLayout:(UICollectionViewLayout *)toLayout;

// Focus
//焦点方法
- (BOOL)collectionView:(UICollectionView *)collectionView canFocusItemAtIndexPath:(NSIndexPath *)indexPath NS_AVAILABLE_IOS(9_0);
- (BOOL)collectionView:(UICollectionView *)collectionView shouldUpdateFocusInContext:(UICollectionViewFocusUpdateContext *)context NS_AVAILABLE_IOS(9_0);
- (void)collectionView:(UICollectionView *)collectionView didUpdateFocusInContext:(UICollectionViewFocusUpdateContext *)context withAnimationCoordinator:(UIFocusAnimationCoordinator *)coordinator NS_AVAILABLE_IOS(9_0);
- (nullable NSIndexPath *)indexPathForPreferredFocusedViewInCollectionView:(UICollectionView *)collectionView NS_AVAILABLE_IOS(9_0);

- (NSIndexPath *)collectionView:(UICollectionView *)collectionView targetIndexPathForMoveFromItemAtIndexPath:(NSIndexPath *)originalIndexPath toProposedIndexPath:(NSIndexPath *)proposedIndexPath NS_AVAILABLE_IOS(9_0);

- (CGPoint)collectionView:(UICollectionView *)collectionView targetContentOffsetForProposedContentOffset:(CGPoint)proposedContentOffset NS_AVAILABLE_IOS(9_0); // customize the content offset to be applied during transition or update animations

@end

• 例子

显示编辑菜单（如复制，粘贴等） 
- (BOOL)  collectionView:(UICollectionView *)collectionView shouldShowMenuForItemAtIndexPath:(NSIndexPath *)indexPath{
    return YES;
}
- (BOOL) collectionView:(UICollectionView *)collectionView  canPerformAction:(SEL)action  forItemAtIndexPath:(NSIndexPath *)indexPath  withSender:(id)sender{
    if (action == @selector(copy:)){  
        return YES;   //此处只显示copy
    }
     return NO;
}
- (void) collectionView:(UICollectionView *)collectionView  performAction:(SEL)action forItemAtIndexPath:(NSIndexPath *)indexPath  withSender:(id)sender{
    if (action == @selector(copy:)){
        MyCollectionViewCell *cell = (MyCollectionViewCell *)[collectionView  cellForItemAtIndexPath:indexPath];
        [[UIPasteboard generalPasteboard] setImage:cell.imageViewBackgroundImage.image];    //剪贴板存储
    }  
}

UICollectionViewDataSource

@protocol UICollectionViewDataSource 
@required

//section包含的item的个数
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section;

// The cell that is returned must be retrieved from a call to -dequeueReusableCellWithReuseIdentifier:forIndexPath:
- (__kindof UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath;

@optional

- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView;

// The view that is returned must be retrieved from a call to -dequeueReusableSupplementaryViewOfKind:withReuseIdentifier:forIndexPath:
// UICollectionReusableView
- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath;

// 是否可以移动item
- (BOOL)collectionView:(UICollectionView *)collectionView canMoveItemAtIndexPath:(NSIndexPath *)indexPath NS_AVAILABLE_IOS(9_0);
//移动item
- (void)collectionView:(UICollectionView *)collectionView moveItemAtIndexPath:(NSIndexPath *)sourceIndexPath toIndexPath:(NSIndexPath*)destinationIndexPath NS_AVAILABLE_IOS(9_0);

@end