UIcollectionView基礎詳解

簡介：UIcollectionView是我們在做iOS高級視圖中經常用到的控件，他的特點就是非常靈活。只要有算法支撐，對於界面布局來說塔五說不能。

1.對比學習：

UIcollectionView還有兩個看是兄弟的控件。NSCollectionView和UITableView，但是他們絕逼不能等效。

2.UIcollectionView的特點介紹：

（1）他可以高度制定內容的展現

（2）能夠高效處理大量數據

3.UIcollectionView的構成元素

（1）Cell（單元格）

（2）Supplementary Views （補充視圖【我們也可以對比tableView，類似於TableView的頁眉和頁腳】）

（3）Decoration Views (裝飾視圖，用於裝飾整個UIcollectionView)

如下圖所示：

 

4.UIcollectionView代理介紹：

（1）UICollectionViewDataSource：（用於為Collection提供數據）

　主要功能：

　　【1】Section數目

　　【2】Section里面有多少item

　　【3】提供Cell和supplementary view（補充視圖）設置

  方法（文檔）：

@protocol UICollectionViewDataSource <NSObject>
@required
//Section個數
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section;
//設置Cell
// The cell that is returned must be retrieved from a call to -dequeueReusableCellWithReuseIdentifier:forIndexPath:
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath;

@optional
//每個section中item的個數
- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView;

// The view that is returned must be retrieved from a call to -dequeueReusableSupplementaryViewOfKind:withReuseIdentifier:forIndexPath:對頭視圖或者尾視圖進行設置
- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath;
//設置某個item是否可以被移動，返回NO則不能移動
- (BOOL)collectionView:(UICollectionView *)collectionView canMoveItemAtIndexPath:(NSIndexPath *)indexPath NS_AVAILABLE_IOS(9_0);
- (void)collectionView:(UICollectionView *)collectionView moveItemAtIndexPath:(NSIndexPath *)sourceIndexPath toIndexPath:(NSIndexPath*)destinationIndexPath NS_AVAILABLE_IOS(9_0);
//移動item的時候，會調用這個方法
@end

@protocol UICollectionViewDelegate <UIScrollViewDelegate>
@optional

// Methods for notification of selection/deselection and highlight/unhighlight events.
// The sequence of calls leading to selection from a user touch is:
//
// (when the touch begins)
// 1. -collectionView:shouldHighlightItemAtIndexPath:
// 2. -collectionView:didHighlightItemAtIndexPath:
//
// (when the touch lifts)
// 3. -collectionView:shouldSelectItemAtIndexPath: or -collectionView:shouldDeselectItemAtIndexPath:
// 4. -collectionView:didSelectItemAtIndexPath: or -collectionView:didDeselectItemAtIndexPath:
// 5. -collectionView:didUnhighlightItemAtIndexPath:
//這個協議用來設置和處理collectionView的功能和一些邏輯，所有方法都是可選實現：是否允許某個Item的高亮，返回NO，則不能進入高亮狀態

- (BOOL)collectionView:(UICollectionView *)collectionView shouldHighlightItemAtIndexPath:(NSIndexPath *)indexPath;
//當item高亮時觸發的方法
- (void)collectionView:(UICollectionView *)collectionView didHighlightItemAtIndexPath:(NSIndexPath *)indexPath;
//結束高亮狀態時觸發的方法
- (void)collectionView:(UICollectionView *)collectionView didUnhighlightItemAtIndexPath:(NSIndexPath *)indexPath;
//是否可以選中某個Item，返回NO，則不能選中
- (BOOL)collectionView:(UICollectionView *)collectionView shouldSelectItemAtIndexPath:(NSIndexPath *)indexPath;
//是否可以取消選中某個Item
- (BOOL)collectionView:(UICollectionView *)collectionView shouldDeselectItemAtIndexPath:(NSIndexPath *)indexPath; // called when the user taps on an already-selected item in multi-select mode
//已經選中某個item時觸發的方法
- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath;
//取消選中某個Item時觸發的方法
- (void)collectionView:(UICollectionView *)collectionView didDeselectItemAtIndexPath:(NSIndexPath *)indexPath;
//將要加載某個Item時調用的方法
- (void)collectionView:(UICollectionView *)collectionView willDisplayCell:(UICollectionViewCell *)cell forItemAtIndexPath:(NSIndexPath *)indexPath NS_AVAILABLE_IOS(8_0);
//將要加載頭尾視圖時調用的方法
- (void)collectionView:(UICollectionView *)collectionView willDisplaySupplementaryView:(UICollectionReusableView *)view forElementKind:(NSString *)elementKind atIndexPath:(NSIndexPath *)indexPath NS_AVAILABLE_IOS(8_0);
//已經展示某個Item時觸發的方法
- (void)collectionView:(UICollectionView *)collectionView didEndDisplayingCell:(UICollectionViewCell *)cell forItemAtIndexPath:(NSIndexPath *)indexPath;
//已經展示某個頭尾視圖時觸發的方法
- (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.

//這個方法設置是否展示長按菜單
- (BOOL)collectionView:(UICollectionView *)collectionView shouldShowMenuForItemAtIndexPath:(NSIndexPath *)indexPath;
//這個方法用於設置要展示的菜單選項
- (BOOL)collectionView:(UICollectionView *)collectionView canPerformAction:(SEL)action forItemAtIndexPath:(NSIndexPath *)indexPath withSender:(nullable id)sender;
//這個方法用於實現點擊菜單按鈕后的觸發方法,通過測試，只有copy，cut和paste三個方法可以使用
- (void)collectionView:(UICollectionView *)collectionView performAction:(SEL)action forItemAtIndexPath:(NSIndexPath *)indexPath withSender:(nullable id)sender;

// support for custom transition layout
//collectionView進行重新布局時調用的方法
- (nonnull UICollectionViewTransitionLayout *)collectionView:(UICollectionView *)collectionView transitionLayoutForOldLayout:(UICollectionViewLayout *)fromLayout newLayout:(UICollectionViewLayout *)toLayout;

// Focus
//焦點
- (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

4.　iOS6之后，Cell重用得到改善

我們可以更加方便的使用Cell，系統總是為我們初始化Cell。我們可以直接使用。只需要簡單的按照兩步走即可：

（1）必須使用下面方法對Cell進行Cell類的注冊：