級別： ★★☆☆☆
標簽：「iOS」「卡片式控件」「QiCardView」
作者： MrLiuQ
審校： QiShare團隊

前言：因項目中需求，需要做一個卡片式控件。故QiCardView誕生了。

首先，先來看一下QiCardView的效果圖：

從命名來看，QiCardView，顧名思義，是一個可定制的卡片式UI控件。
從設計來看，QiCardView仿照UITableView的設計，支持cell復用，節省了資源。

話不多說，先來看下整體架構~

一、QiCardView整體架構設計

架構層面仿照了UITableView的設計，采用了cell復用策略。
在此基礎上，融入了一些手勢操作，更加富有交互性。

上架構圖：

兩個主類分別為QiCardView與QiCardViewCell。（仿照UITableView+UITableViewCell的設計）

• QiCardView下有兩個代理：QiCardViewDataSource、QiCardViewDelegate。（與UITableView的代理方法類似）
• QiCardViewCell下有一個代理：QiCardViewCellDelegate。（這個代理可以不關心，主要目的是輔助QiCardView里的一些處理邏輯）

二、如何自定義使用QiCardView？

Cell自定義很簡單，只要新建一個類（例如：QiCardViewItemCell）繼承自QiCardViewCell即可。

在Controller中，基本使用上幾乎與UITableView類似。

• 初始化CardView方法：

在上Demo之前，先介紹幾個可以自定義的配置屬性：

- (void)initViews {
    
    _cardView = [[QiCardView alloc] initWithFrame:CGRectMake(25.0, 150.0, self.view.frame.size.width - 50.0, 420.0)];
    _cardView.backgroundColor = [UIColor lightGrayColor];//!< 為了指出carddView的區域，指明背景色
    _cardView.dataSource = self;
    _cardView.delegate = self;
    _cardView.visibleCount = 4;
    _cardView.lineSpacing = 15.0;
    _cardView.interitemSpacing = 10.0;
    _cardView.maxAngle = 10.0;
    _cardView.isAlpha = YES;
    _cardView.maxRemoveDistance = 100.0;
    _cardView.layer.cornerRadius = 10.0;
    [_cardView registerClass:[QiCardItemCell class] forCellReuseIdentifier:qiCardCellId];
    [self.view addSubview:_cardView];
}

• 數據源：QiCardViewDataSource：
  首先controller要遵守協議：<QiCardViewDataSource>

#pragma mark - QiCardViewDataSource

- (QiCardItemCell *)cardView:(QiCardView *)cardView cellForRowAtIndex:(NSInteger)index {
    
    QiCardItemCell *cell = [cardView dequeueReusableCellWithIdentifier:qiCardCellId];
    cell.cellData = _cellItems[index];
    //...

    return cell;
}

- (NSInteger)numberOfCountInCardView:(UITableView *)cardView {
    return _cellItems.count;
}

• 代理：QiCardViewDelegate：
  還是首先controller需要遵守協議：<QiCardViewDelegate>。

#pragma mark - QiCardViewDelegate

- (void)cardView:(QiCardView *)cardView didRemoveLastCell:(QiCardViewCell *)cell forRowAtIndex:(NSInteger)index {
    [cardView reloadDataAnimated:YES];
}

- (void)cardView:(QiCardView *)cardView didRemoveCell:(QiCardViewCell *)cell forRowAtIndex:(NSInteger)index {
    NSLog(@"didRemoveCell forRowAtIndex = %ld", index);
}

- (void)cardView:(QiCardView *)cardView didDisplayCell:(QiCardViewCell *)cell forRowAtIndex:(NSInteger)index {
    
    NSLog(@"didDisplayCell forRowAtIndex = %ld", index);
}

- (void)cardView:(QiCardView *)cardView didMoveCell:(QiCardViewCell *)cell forMovePoint:(CGPoint)point {
    NSLog(@"move point = %@", NSStringFromCGPoint(point));
}

三、QiCardView的技術點

3.1 QiCardViewCell復用策略實現

1. 注冊Cell：
   兩種方式：registerNib、registerClass。 很簡單。

/** 注冊cell方法一：Nib */
- (void)registerNib:(nullable UINib *)nib forCellReuseIdentifier:(NSString *)identifier {
    self.nib = nib;
    self.identifier = identifier;
}

/** 注冊cell方法二：Class */
- (void)registerClass:(nullable Class)cellClass forCellReuseIdentifier:(NSString *)identifier {
    self.cellClass = cellClass;
    self.identifier = identifier;
}

2. 獲取緩存Cell策略：
   先看緩存池中是否有相同ID（identifier）的Cell，有的話，直接返回Cell。
   若緩存池中沒有，那么就new一個新的Cell啦~

/** 獲取緩存cell */
- (__kindof QiCardViewCell *)dequeueReusableCellWithIdentifier:(NSString *)identifier {
    for (QiCardViewCell *cell in self.reusableCells) {
        if ([cell.reuseIdentifier isEqualToString:identifier]) {
            [self.reusableCells removeObject:cell];
            
            return cell;
        }
    }
    if (self.nib) {
        QiCardViewCell *cell = [[self.nib instantiateWithOwner:nil options:nil] lastObject];
        cell.reuseIdentifier = identifier;
        
        return cell;
    } else if (self.cellClass) { // 注冊class
        QiCardViewCell *cell = [[self.cellClass alloc] initWithReuseIdentifier:identifier];
        cell.reuseIdentifier = identifier;
        
        return cell;
    }
    return nil;
}

3. 當cell走DidRemoveFromSuperView方法時，把cell加入緩存池。

- (void)cardViewCellDidRemoveFromSuperView:(QiCardViewCell *)cell {

    //...    

    [self.reusableCells addObject:cell];

    //...
}

3.2 cell重疊透明度漸變的實現

1. 首先聲明了一個靜態變量：moveCount來記錄翻卡次數。（以便將cell的index與卡片的index邏輯關聯）

static int moveCount = 0;//!< 記錄翻頁次數

2. 邏輯：每個CardCell 在 “remove from super view” 的時候 moveCount+1。

#pragma mark - QiCardViewCellDelagate

- (void)cardViewCellDidRemoveFromSuperView:(QiCardViewCell *)cell {
    
    moveCount++;
    
    //....
}

3. 邏輯：在reload方法中，需要將moveCount置0。（很好理解，reload時，moveCount需要重新開始計算）

- (void)reloadDataAnimated:(BOOL)animated {
    
    moveCount = 0;//!< 漸變需要
    
   //...
}

4. 關鍵邏輯：在每次更新布局時，設置每個Cell的漸變值（即alpha）

/** 更新布局（動畫） */
- (void)updateLayoutVisibleCellsWithAnimated:(BOOL)animated {
    
    //...

    if (_isAlpha) {
        BOOL isTopCell = (i == _currentIndex - moveCount);
        if (isTopCell) {//!< 如果是最上面的Cell就透明度為1
            cell.alpha = 1.0;
         } else {
            cell.alpha = (i + 1.9) * 1.0/self.visibleCells.count;
        }
    }

    //...

}

3.3 手勢操作實現

這部分主要是手勢+動畫。
細節比較多，小而雜。
詳細邏輯，請見源碼。

#define Qi_SNAPSHOTVIEW_TAG 999
#define Qi_DEGREES_TO_RADIANS(angle) (angle / 180.0 * M_PI)

- (void)panGestureRecognizer:(UIPanGestureRecognizer*)pan {
    
    switch (pan.state) {
        case UIGestureRecognizerStateBegan:
            self.currentPoint = CGPointZero;
            break;
        case UIGestureRecognizerStateChanged: {
            CGPoint movePoint = [pan translationInView:pan.view];
            self.currentPoint = CGPointMake(self.currentPoint.x + movePoint.x , self.currentPoint.y + movePoint.y);
            
            CGFloat moveScale = self.currentPoint.x / self.maxRemoveDistance;
            if (ABS(moveScale) > 1.0) {
                moveScale = (moveScale > 0) ? 1.0 : -1.0;
            }
            CGFloat angle = Qi_DEGREES_TO_RADIANS(self.maxAngle) * moveScale;
            CGAffineTransform transRotation = CGAffineTransformMakeRotation(angle);
            self.transform = CGAffineTransformTranslate(transRotation, self.currentPoint.x, self.currentPoint.y);
            
            if (self.cell_delegate && [self.cell_delegate respondsToSelector:@selector(cardViewCellDidMoveFromSuperView:forMovePoint:)]) {
                [self.cell_delegate cardViewCellDidMoveFromSuperView:self forMovePoint:self.currentPoint];
            }
            [pan setTranslation:CGPointZero inView:pan.view];
        }
            break;
        case UIGestureRecognizerStateEnded:
            [self didPanStateEnded];
            break;
        case UIGestureRecognizerStateCancelled:
        case UIGestureRecognizerStateFailed:
            [self restoreCellLocation];
            break;
        default:
            break;
    }
}

// 手勢結束操作（不考慮上下位移）
- (void)didPanStateEnded {
    // 右滑移除
    if (self.currentPoint.x > self.maxRemoveDistance) {
        __block UIView *snapshotView = [self snapshotViewAfterScreenUpdates:NO];
        snapshotView.transform = self.transform;
        [self.superview.superview addSubview:snapshotView];
        [self didCellRemoveFromSuperview];
        
        CGFloat endCenterX = [UIScreen mainScreen].bounds.size.width/2 + self.frame.size.width * 1.5;
        [UIView animateWithDuration:Qi_DefaultDuration animations:^{
            CGPoint center = self.center;
            center.x = endCenterX;
            snapshotView.center = center;
        } completion:^(BOOL finished) {
            [snapshotView removeFromSuperview];
        }];
    }
    // 左滑移除
    else if (self.currentPoint.x < -self.maxRemoveDistance) {
        __block UIView *snapshotView = [self snapshotViewAfterScreenUpdates:NO];
        snapshotView.transform = self.transform;
        [self.superview.superview addSubview:snapshotView];
        [self didCellRemoveFromSuperview];
        
        CGFloat endCenterX = -([UIScreen mainScreen].bounds.size.width/2 + self.frame.size.width);
        [UIView animateWithDuration:Qi_DefaultDuration animations:^{
            CGPoint center = self.center;
            center.x = endCenterX;
            snapshotView.center = center;
        } completion:^(BOOL finished) {
            [snapshotView removeFromSuperview];
        }];
    }
    // 滑動距離不夠歸位
    else {
        [self restoreCellLocation];
    }
}

// 還原卡片位置
- (void)restoreCellLocation {
    
    [UIView animateWithDuration:Qi_SpringDuration delay:0
         usingSpringWithDamping:Qi_SpringWithDamping
          initialSpringVelocity:Qi_SpringVelocity
                        options:UIViewAnimationOptionCurveEaseOut
                     animations:^{
                         self.transform = CGAffineTransformIdentity;
                     } completion:nil];
}

// 卡片移除處理
- (void)didCellRemoveFromSuperview {
    
    self.transform = CGAffineTransformIdentity;
    [self removeFromSuperview];
    if ([self.cell_delegate respondsToSelector:@selector(cardViewCellDidRemoveFromSuperView:)]) {
        [self.cell_delegate cardViewCellDidRemoveFromSuperView:self];
    }
}

- (void)removeFromSuperviewSwipe:(QiCardCellSwipeDirection)direction {
    
    switch (direction) {
        case QiCardCellSwipeDirectionLeft: {
            [self removeFromSuperviewLeft];
        }
            break;
        case QiCardCellSwipeDirectionRight: {
            [self removeFromSuperviewRight];
        }
            break;
        default:
            break;
    }
}

// 向左邊移除動畫
- (void)removeFromSuperviewLeft {
    __block UIView *snapshotView = [self snapshotViewAfterScreenUpdates:NO];
    [self.superview.superview addSubview:snapshotView];
    [self didCellRemoveFromSuperview];
    
    CGAffineTransform transRotation = CGAffineTransformMakeRotation(-Qi_DEGREES_TO_RADIANS(self.maxAngle));
    CGAffineTransform transform = CGAffineTransformTranslate(transRotation, 0, self.frame.size.height/4.0);
    CGFloat endCenterX = -([UIScreen mainScreen].bounds.size.width/2 + self.frame.size.width);
    [UIView animateWithDuration:Qi_DefaultDuration animations:^{
        CGPoint center = self.center;
        center.x = endCenterX;
        snapshotView.center = center;
        snapshotView.transform = transform;
    } completion:^(BOOL finished) {
        [snapshotView removeFromSuperview];
    }];
}

// 向右邊移除動畫
- (void)removeFromSuperviewRight {
    __block UIView *snapshotView = [self snapshotViewAfterScreenUpdates:NO];
    snapshotView.frame = self.frame;
    [self.superview.superview addSubview:snapshotView];
    [self didCellRemoveFromSuperview];
    
    CGAffineTransform transRotation = CGAffineTransformMakeRotation(Qi_DEGREES_TO_RADIANS(self.maxAngle));
    CGAffineTransform transform = CGAffineTransformTranslate(transRotation, 0, self.frame.size.height/4.0);
    CGFloat endCenterX = [UIScreen mainScreen].bounds.size.width/2 + self.frame.size.width * 1.5;
    [UIView animateWithDuration:Qi_DefaultDuration animations:^{
        CGPoint center = self.center;
        center.x = endCenterX;
        snapshotView.center = center;
        snapshotView.transform = transform;
    } completion:^(BOOL finished) {
        [snapshotView removeFromSuperview];
    }];
}

四、未來可能優化的點

• 設計層面：如果將手勢操作融入QiCardView中，將QiCardViewCell變成純粹的Cell，會不會更好。（思考中）
• 應用層面：目前只支持一個ID的Cell重用，未來渴望拓展成多個ID的Cell都可重用。（PS：因為只存了一個ID，后續考慮存數組，以及對應的Cell緩存池數組。以此猜測UITableView的內部實現。）

源碼：QiCardView源碼。

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