如何将 UIScrollView 的触摸事件发送到它背后的视图？

Question

我在另一个视图之上有一个透明的 UIScrollView。

滚动视图有内容——文本和图像，用于显示信息。

它背后的视图有一些用户应该能够点击的图像。 并且它们上面的内容可以使用提到的滚动视图滚动。

我希望能够正常使用滚动视图（虽然没有缩放），但是当滚动视图实际上没有滚动时，让点击事件进入它后面的视图。

结合使用触摸和滚动事件，我可以确定何时让点击通过。 但是它背后的视图仍然没有收到它们。

我已经尝试对所有触摸事件使用类似的东西：

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event 
{
    NSLog(@"touchesBegan %@", (_isScrolling ? @"YES" : @"NO"));

    if(!_isScrolling) 
    {
        NSLog(@"sending");
        [self.viewBehind touchesBegan:touches withEvent:event];
    }
}

但它不起作用。

在我的情况下，考虑到我的用例，我也不能真正应用 hitTest 和 pointInside 解决方案。

Answer 1

首先UIScrollViews 只能识别UIPanGestureRecognizers 和UIPinchGestureRecognizers，因此您需要在UIScrollView 中添加UITapGestureRecognizer，以便它也可以识别任何点击手势：

UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(handleTap:)];

// To prevent the pan gesture of the UIScrollView from swallowing up the
// touch event
tap.cancelsTouchesInView = NO;

[scrollView addGestureRecognizer:tap];

然后，一旦您收到该点击手势并触发handleTap: 操作，您可以使用locationInView: 来检测点击手势的位置是否实际上在滚动视图下方的其中一个图像的框架内，例如：

- (void)handleTap:(UITapGestureRecognizer *)recognizer {

    // First get the tap gesture recognizers's location in the entire 
    // view's window
    CGPoint tapPoint = [recognizer locationInView:self.view];

    // Then see if it falls within one of your below images' frames
    for (UIImageView* image in relevantImages) {

        // If the image's coordinate system isn't already equivalent to
        // self.view, convert it so it has the same coordinate system
        // as the tap.
        CGRect imageFrameInSuperview = [image.superview convertRect:image toView:self.view]

        // If the tap in fact lies inside the image bounds, 
        // perform the appropriate action.
        if (CGRectContainsPoint(imageFrameInSuperview, tapPoint)) {
            // Perhaps call a method here to react to the image tap
            [self reactToImageTap:image];
            break;
        }
    }
}

这样，上面的代码仅在识别到点击手势时执行，如果点击位置落在图像内，您的程序只会对滚动视图上的点击做出反应；否则，您可以像往常一样滚动UIScrollView。

Answer 2

在这里我提出我的完整解决方案：

• 直接向前触摸视图而不是调用控件事件。
• 用户可以指定要转发的类。
• 如果需要转发，用户可以指定检查哪些视图。

界面如下：

/**
 * This subclass of UIScrollView allow views in a deeper Z index to react when touched, even if the scrollview instance is in front of them.
 **/
@interface MJForwardingTouchesScrollView : UIScrollView

/**
 * Set of Class objects. The scrollview will events pass through if the initial tap is not over a view of the specified classes.
 **/
@property (nonatomic, strong) NSSet <Class> *forwardsTouchesToClasses;

/**
 * Optional array of underlying views to test touches forward. Default is nil.
 * @discussion By default the scroll view will attempt to forward to views located in the same self.superview.subviews array. However, optionally by providing specific views inside this property, the scroll view subclass will check als among them.
 **/
@property (nonatomic, strong) NSArray <__kindof UIView*> *underlyingViews;

@end

以及实施：

#import "MJForwardingTouchesScrollView.h"
#import "UIView+Additions.h"

@implementation MJForwardingTouchesScrollView

- (instancetype)initWithCoder:(NSCoder *)aDecoder
{
    self = [super initWithCoder:aDecoder];
    if (self != nil)
    {
        _forwardsTouchesToClasses = [NSSet setWithArray:@[UIControl.class]];
    }
    return self;
}

- (instancetype)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self != nil)
    {
        _forwardsTouchesToClasses = [NSSet setWithArray:@[UIControl.class]];
    }
    return self;
}

- (BOOL)pointInside:(CGPoint)point withEvent:(UIEvent *)event
{
    BOOL pointInside = [self mjz_mustCapturePoint:point withEvent:event];

    if (!pointInside)
        return NO;

    return [super pointInside:point withEvent:event];
}

#pragma mark Private Methods

- (BOOL)mjz_mustCapturePoint:(CGPoint)point withEvent:(UIEvent*)event
{
    if (![self mjz_mustCapturePoint:point withEvent:event view:self.superview])
        return NO;

    __block BOOL mustCapturePoint = YES;
    [_underlyingViews enumerateObjectsUsingBlock:^(__kindof UIView * _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
        if (![self mjz_mustCapturePoint:point withEvent:event view:obj])
        {
            mustCapturePoint = NO;
            *stop = YES;
        }
    }];

    return mustCapturePoint;
}

- (BOOL)mjz_mustCapturePoint:(CGPoint)point withEvent:(UIEvent *)event view:(UIView*)view
{
    CGPoint tapPoint = [self convertPoint:point toView:view];

    __block BOOL mustCapturePoint = YES;
    [view add_enumerateSubviewsPassingTest:^BOOL(UIView * _Nonnull testView) {
        BOOL forwardTouches = [self mjz_forwardTouchesToClass:testView.class];
        return forwardTouches;
    } objects:^(UIView * _Nonnull testView, BOOL * _Nullable stop) {
        CGRect imageFrameInSuperview = [testView.superview convertRect:testView.frame toView:view];

        if (CGRectContainsPoint(imageFrameInSuperview, tapPoint))
        {
            mustCapturePoint = NO;
            *stop = YES;
        }
    }];

    return mustCapturePoint;
}

- (BOOL)mjz_forwardTouchesToClass:(Class)class
{
    while ([class isSubclassOfClass:NSObject.class])
    {
        if ([_forwardsTouchesToClasses containsObject:class])
            return YES;

        class = [class superclass];
    }
    return NO;
}

@end

唯一使用的额外代码在UIView+Additions.h类别内，其中包含以下方法：

- (void)add_enumerateSubviewsPassingTest:(BOOL (^_Nonnull)(UIView * _Nonnull view))testBlock
                                 objects:(void (^)(id _Nonnull obj, BOOL * _Nullable stop))block
{
    if (!block)
        return;

    NSMutableArray *array = [NSMutableArray array];
    [array addObject:self];

    while (array.count > 0)
    {
        UIView *view = [array firstObject];
        [array removeObjectAtIndex:0];

        if (view != self && testBlock(view))
        {
            BOOL stop = NO;
            block(view, &stop);
            if (stop)
                return;
        }

        [array addObjectsFromArray:view.subviews];
    }
}

谢谢

Answer 3

问题是您的UIScrollView 正在使用该事件。要通过它，您必须禁用用户对其的交互，但它不会滚动。但是，如果您有触摸位置，则可以使用convertPoint:toView: 方法计算它落在底层视图的哪个位置，并通过传递CGPoint 对其调用一个数学方法。从那里，您可以计算出被点击的图像。