在含大量可点击ImageView的UIScrollView中如何提升性能？

方案1：给UIScrollView添加单个全局点击手势 #

放弃给每个ImageView单独加手势，转而给UIScrollView添加一个点击手势，通过点击位置匹配对应的ImageView，彻底减少手势数量。

实现步骤：

• 给UIScrollView绑定一个UITapGestureRecognizer
• 在手势回调中，将点击坐标转换为ScrollView内容坐标系下的点（需考虑contentOffset）
• 遍历预存的ImageView数组，判断点击点是否落在目标ImageView的frame内，触发对应点击逻辑

代码示例：

// 初始化时添加全局手势
UITapGestureRecognizer *globalTap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(onScrollViewTap:)];
[self.scrollView addGestureRecognizer:globalTap];

// 手势处理逻辑
- (void)onScrollViewTap:(UITapGestureRecognizer *)gesture {
    CGPoint tapPoint = [gesture locationInView:self.scrollView];
    // 转换为内容区域坐标
    CGPoint contentPoint = CGPointMake(tapPoint.x + self.scrollView.contentOffset.x, 
                                      tapPoint.y + self.scrollView.contentOffset.y);
    
    for (UIImageView *imgView in self.allImageViews) { // allImageViews是提前存储所有ImageView的数组
        if (CGRectContainsPoint(imgView.frame, contentPoint)) {
            [self handleImageViewTap:imgView];
            break;
        }
    }
}

- (void)handleImageViewTap:(UIImageView *)imageView {
    // 执行ImageView的点击业务逻辑
}

方案2：按需添加/移除ImageView手势 #

仅给当前可见区域内的ImageView添加手势，滑出屏幕时移除手势，控制同时存在的手势数量。

实现步骤：

• 监听UIScrollView的滚动事件（KVO或代理方法）
• 计算当前ScrollView的可见区域
• 遍历ImageView数组，给可见的ImageView添加手势，给不可见的移除手势

代码示例：

// 初始化时监听滚动
[self.scrollView addObserver:self forKeyPath:@"contentOffset" options:NSKeyValueObservingOptionNew context:nil];

// KVO回调处理
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSKeyValueChangeKey,id> *)change context:(void *)context {
    if ([keyPath isEqualToString:@"contentOffset"]) {
        [self updateImageViewGestures];
    }
}

// 按需更新手势
- (void)updateImageViewGestures {
    CGRect visibleRect = CGRectMake(self.scrollView.contentOffset.x, 
                                   self.scrollView.contentOffset.y, 
                                   self.scrollView.bounds.size.width, 
                                   self.scrollView.bounds.size.height);
    
    for (UIImageView *imgView in self.allImageViews) {
        BOOL isVisible = CGRectIntersectsRect(imgView.frame, visibleRect);
        if (isVisible) {
            if (imgView.gestureRecognizers.count == 0) {
                UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(handleImageViewTap:)];
                [imgView addGestureRecognizer:tap];
            }
        } else {
            [imgView removeAllGestureRecognizers];
        }
    }
}

// 给UIView添加移除所有手势的分类
@implementation UIView (GestureHelper)
- (void)removeAllGestureRecognizers {
    while (self.gestureRecognizers.count > 0) {
        [self removeGestureRecognizer:self.gestureRecognizers.firstObject];
    }
}
@end

方案3：重写ScrollView的触摸事件处理 #

通过自定义ScrollView子类，重写hitTest:和touchesEnded:方法，直接拦截触摸事件并匹配目标ImageView，无需依赖手势识别器。

代码示例：

// 自定义ScrollView类
@interface CustomScrollView : UIScrollView
@property (nonatomic, weak) id<CustomScrollViewTapDelegate> tapDelegate;
@end

@protocol CustomScrollViewTapDelegate <NSObject>
- (void)scrollView:(CustomScrollView *)scrollView didTapImageView:(UIImageView *)imageView;
@end

@implementation CustomScrollView

// 命中测试，找到被点击的ImageView
- (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event {
    UIView *hitView = [super hitTest:point withEvent:event];
    return [hitView isKindOfClass:[UIImageView class]] ? hitView : self;
}

// 处理触摸结束事件
- (void)touchesEnded:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    UITouch *touch = touches.anyObject;
    CGPoint point = [touch locationInView:self];
    UIView *hitView = [self hitTest:point withEvent:event];
    
    if ([hitView isKindOfClass:[UIImageView class]] && [_tapDelegate respondsToSelector:@selector(scrollView:didTapImageView:)]) {
        [_tapDelegate scrollView:self didTapImageView:(UIImageView *)hitView];
    } else {
        [super touchesEnded:touches withEvent:event];
    }
}

@end

额外优化点 #

1. 提前将所有ImageView存入数组，避免每次遍历ScrollView的所有子视图，减少遍历开销
2. 方案2中可添加滚动节流逻辑，比如在滚动停止后再更新手势，避免滚动过程中频繁操作手势
3. 确保ImageView的userInteractionEnabled仅在需要时设为YES，减少不必要的触摸响应

内容的提问来源于stack exchange，提问作者Curiosity