UICollectionView詳解之基礎使用介紹

UICollectionView簡介

UICollectionView在iOS6.0以后引進,與UITableView比較相似。但是UICollectionView將布局完全交給UICollectionViewLayout，而且允許用戶自定義layout來進行布局。使其功能比UITableView更加強大、布局更加靈活，迅速在各大APP廣泛使用。

本篇將對UICollectionView的使用進行簡單介紹，主要包括UICollectionView的視圖組成、數據源、常用代理方法以及UICollectionViewFlowLayout的使用。下一遍將會詳細講解UICollectionViewLayout的自定義布局。

UICollectionView的視圖組成：

UICollectionView由cell視圖、Supplementary View和Decoration View三部分組成。

cell視圖

這個大家應該都很清楚，UICollectionView主要內容展示的視圖

Supplementary View

對于每組section的信息視圖，類似于UITableView的header或者footer

Decoration View

裝飾視圖，好像很少使用

cell視圖跟Supplementary View使用是需要先進行注冊以便實現復用：

注冊cell的方法，第一個是代碼創建，第二個是xib創建
- (void)registerClass:(nullable Class)cellClass forCellWithReuseIdentifier:(NSString *)identifier;
- (void)registerNib:(nullable UINib *)nib forCellWithReuseIdentifier:(NSString *)identifier;

注冊Supplementary View的方法，第一個是代碼創建，第二個是xib創建
- (void)registerClass:(nullable Class)viewClass forSupplementaryViewOfKind:(NSString *)elementKind withReuseIdentifier:(NSString *)identifier;
- (void)registerNib:(nullable UINib *)nib forSupplementaryViewOfKind:(NSString *)kind withReuseIdentifier:(NSString *)identifier;

在數據源回調中復用的方法：
- (__kindof UICollectionViewCell *)dequeueReusableCellWithReuseIdentifier:(NSString *)identifier forIndexPath:(NSIndexPath *)indexPath;
- (__kindof UICollectionReusableView *)dequeueReusableSupplementaryViewOfKind:(NSString *)elementKind withReuseIdentifier:(NSString *)identifier forIndexPath:(NSIndexPath *)indexPath;

***上面方法的的kind和elementKind參數用來區分是頭部視圖還是尾部視圖

UICollectionView的數據源代理方法：

//必須實現的數據源代理
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section;
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath;


//可選數據源代理
- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView;
- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath;
處理移動相關（詳細使用看demo）
- (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);

UICollectionView的常用代理方法：

//點擊cell高亮相關
- (BOOL)collectionView:(UICollectionView *)collectionView shouldHighlightItemAtIndexPath:(NSIndexPath *)indexPath;
- (void)collectionView:(UICollectionView *)collectionView didHighlightItemAtIndexPath:(NSIndexPath *)indexPath;
- (void)collectionView:(UICollectionView *)collectionView didUnhighlightItemAtIndexPath:(NSIndexPath *)indexPath;


//cell選中相關
- (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;


//cell以及Supplementary View繪制相關
- (void)collectionView:(UICollectionView *)collectionView willDisplayCell:(UICollectionViewCell *)cell forItemAtIndexPath:(NSIndexPath *)indexPath NS_AVAILABLE_IOS(8_0);
- (void)collectionView:(UICollectionView *)collectionView willDisplaySupplementaryView:(UICollectionReusableView *)view forElementKind:(NSString *)elementKind atIndexPath:(NSIndexPath *)indexPath NS_AVAILABLE_IOS(8_0);
- (void)collectionView:(UICollectionView *)collectionView didEndDisplayingCell:(UICollectionViewCell *)cell forItemAtIndexPath:(NSIndexPath *)indexPath;
- (void)collectionView:(UICollectionView *)collectionView didEndDisplayingSupplementaryView:(UICollectionReusableView *)view forElementOfKind:(NSString *)elementKind atIndexPath:(NSIndexPath *)indexPath;
***這幾個方法可以添加簡易的動畫,例如添加如下幾句代碼，cell加載的時候將會有放縮等效果。
- (void)collectionView:(UICollectionView *)collectionView willDisplayCell:(UICollectionViewCell *)cell forItemAtIndexPath:(NSIndexPath *)indexPath NS_AVAILABLE_IOS(8_0)
{
    cell.contentView.alpha = 0;
    cell.transform = CGAffineTransformRotate(CGAffineTransformMakeScale(0, 0), 0);

    [UIView animateKeyframesWithDuration:.5 delay:0.0 options:0 animations:^{
        
        /**
         *  分步動畫   第一個參數是該動畫開始的百分比時間  第二個參數是該動畫持續的百分比時間
         */
        [UIView addKeyframeWithRelativeStartTime:0.0 relativeDuration:0.8 animations:^{
            cell.contentView.alpha = .5;
            cell.transform = CGAffineTransformRotate(CGAffineTransformMakeScale(1.2, 1.2), 0);
        }];
        [UIView addKeyframeWithRelativeStartTime:0.8 relativeDuration:0.2 animations:^{
            cell.contentView.alpha = 1;
            cell.transform = CGAffineTransformRotate(CGAffineTransformMakeScale(1, 1), 0);

        }];

    } completion:^(BOOL finished) {
        
    }];
}

//長按顯示菜單相關：(demo中有詳細使用)
- (BOOL)collectionView:(UICollectionView *)collectionView shouldShowMenuForItemAtIndexPath:(NSIndexPath *)indexPath;
- (BOOL)collectionView:(UICollectionView *)collectionView canPerformAction:(SEL)action forItemAtIndexPath:(NSIndexPath *)indexPath withSender:(nullable id)sender;
- (void)collectionView:(UICollectionView *)collectionView performAction:(SEL)action forItemAtIndexPath:(NSIndexPath *)indexPath withSender:(nullable id)sender;

//轉場相關（下一篇會講解）
- (nonnull UICollectionViewTransitionLayout *)collectionView:(UICollectionView *)collectionView transitionLayoutForOldLayout:(UICollectionViewLayout *)fromLayout newLayout:(UICollectionViewLayout *)toLayout;

UICollectionViewFlowLayout && UICollectionViewLayout：

UICollectionView之所以比UITableView強大，主要在于其精髓UICollectionViewLayout的布局。它通過 UICollectionViewLayoutAttributes 類來管理 cell 、 Supplementary View 和 Decoration View 的 位置 、 transform 、 alpha 、 hidden 等等。先看看系統為我們提供的UICollectionViewFlowLayout布局的使用吧。

UICollectionViewFlowLayout 的常用屬性

//決定了每行的間隔
@property (nonatomic) CGFloat minimumLineSpacing;
//決定了Item之間的間隔
@property (nonatomic) CGFloat minimumInteritemSpacing;
//cell的大?。ㄈ绻麑崿F的代理該設置無效）
@property (nonatomic) CGSize itemSize;
//cell大小的預計算
@property (nonatomic) CGSize estimatedItemSize NS_AVAILABLE_IOS(8_0); // defaults to CGSizeZero - setting a non-zero size enables cells that self-size via -preferredLayoutAttributesFittingAttributes:
//布局的方向
@property (nonatomic) UICollectionViewScrollDirection scrollDirection; // default is UICollectionViewScrollDirectionVertical
//頭視圖跟尾視圖的大?。M向的時候，headerReferenceSize.width有效，headerReferenceSize.height無效。縱向時相反）
@property (nonatomic) CGSize headerReferenceSize;
@property (nonatomic) CGSize footerReferenceSize;
//間距
@property (nonatomic) UIEdgeInsets sectionInset;

// Set these properties to YES to get headers that pin to the top of the screen and footers that pin to the bottom while scrolling (similar to UITableView).
@property (nonatomic) BOOL sectionHeadersPinToVisibleBounds NS_AVAILABLE_IOS(9_0);
@property (nonatomic) BOOL sectionFootersPinToVisibleBounds NS_AVAILABLE_IOS(9_0);

UICollectionViewFlowLayout 的代理方法

//基本就是上面的屬性通過代理的方法返回
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath;
- (UIEdgeInsets)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout insetForSectionAtIndex:(NSInteger)section;
- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout minimumLineSpacingForSectionAtIndex:(NSInteger)section;
- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout minimumInteritemSpacingForSectionAtIndex:(NSInteger)section;
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout referenceSizeForHeaderInSection:(NSInteger)section;
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout referenceSizeForFooterInSection:(NSInteger)section;

下一篇UICollectionViewLayout的自定義

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