UIView 中的控件事件穿透 Passthrough 的实现

我们在有多个 UIView 层叠时，比如一个按钮被一个 UIView 遮盖时，想要在点击最上层的 UIView 时能触发按钮的相应事件，我们该如何实现呢，初步可以想到几种办法：

1. 把按钮上层的所有 UIView 的 userInteractionEnabled 属性设置为 NO，要是 UIView 有自己的交互事件该如何办呢？而且这个 userInteractionEnabled 不能动态设置，等到点击后决定设置它的 NO 是没用的

2. UIView 接受到点击事件后主动去触发下面按钮的点击，这时的关题有三，按钮没有点击过程中的交换效果、多层 UIView 时不切实际，逐层下传吗、还有就是其他双击、三击或别的手势如何处理

我也一直被前面两种方式纠缠着，同时也让 UIPopoverController 的 NSArray *passthroughViews 属性提醒着，因为对于 UIPopoverController，设置到它的 passthoughViews 属性中的控件事件可以完全从 UIDimmingView 下透出来。但苦于不可能看到 UIPopoverController 的源码，还是后面一而再的 Google 终于发现了 UIView 的方法：

- (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event;   // recursively calls -pointInside:withEvent:. point is in the receiver's coordinate system

只要实现了最顶层的 UIView 的 hitTest 方法，在某些情况返回下层的某个按钮实例，即相当于把那个按钮的事件透出来了，比如在点击落在该按钮上时，不管这个按钮在 UIView 下多少层都可以把它挖出来。

先看效果图：

三个图分别是：

1. 所见到的，按钮被半透明红色 View 遮住了一部分
2. 可点击未遮住的按钮部分，可看到按钮被点下未抬起的效果
3. 在红色的 View 中点击按钮被遮住部分，同样触发了按钮的相应事件，且有中间效果，也就是说按钮穿透出来了

再看代码实现，有两部分代码，分别是 ViewController 和  CustomController

ViewController.h

//
//  ViewController.h

//
//  Created by Unmi on 11/15/11.
//  Copyright (c) 2011 http://unmi.cc. All rights reserved.
//

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController {
}

@end

ViewController.h

//
//  ViewController.m
//
//  Created by Unmi on 11/15/11.
//  Copyright (c) 2011 http://unmi.cc. All rights reserved.
//

#import "ViewController.h"
#import "CustomView.h"

@implementation ViewController{
    UIButton *passthroughButton;
}

#pragma mark - View lifecycle

- ( void )viewDidLoad
{
    [ super viewDidLoad];

    passthroughButton = [ UIButton buttonWithType: UIButtonTypeRoundedRect ];
    [passthroughButton setTitle:@ "Passthrough" forState: UIControlStateNormal ];
    [ self .view addSubview:passthroughButton];
    passthroughButton.frame = CGRectMake(20, 50, 120, 28);
    [passthroughButton release];

    CustomView *customView = [[CustomView alloc] initWithFrame:CGRectMake(80, 10, 300, 200)];
    customView.backgroundColor = [ UIColor colorWithRed:1 green:0 blue:0 alpha:.5];
    customView.passthroughViews = [ NSArray arrayWithObject:passthroughButton];
    [ self .view addSubview:customView];
    [customView release];
}

- ( void )dealloc {
    [ super dealloc];
}
@end

CustomView.h

//
//  CustomView.h
//  TestPopover
//
//  Created by Unmi on 2/19/12.
//  Copyright (c) 2012 http://unmi.cc. All rights reserved.
//

#import <UIKit/UIKit.h>

@interface CustomView : UIView
@property ( nonatomic , copy ) NSArray *passthroughViews;
@end

CustomView.m

//
//  CustomView.m
//
//  Created by Unmi on 2/19/12.
//  Copyright (c) 2012 http://unmi.cc. All rights reserved.
//

#import "CustomView.h"

@interface CustomView()
-( BOOL ) isPassthroughView: ( UIView *) view;
@end

@implementation CustomView{
    BOOL testHits;
}

@synthesize passthroughViews=_passthroughViews;

-( UIView *) hitTest:(CGPoint)point withEvent:( UIEvent *)event{
    if (testHits){
        return nil ;
    }

    if (! self .passthroughViews
        || ( self .passthroughViews && self .passthroughViews.count == 0)){
        return self ;
    } else {

        UIView *hitView = [ super hitTest:point withEvent:event];

        if (hitView == self ) {
            //Test whether any of the passthrough views would handle this touch
            testHits = YES ;
            CGPoint superPoint = [ self .superview convertPoint:point fromView: self ];
            UIView *superHitView = [ self .superview hitTest:superPoint withEvent:event];
            testHits = NO ;

            if ([ self isPassthroughView:superHitView]) {
                hitView = superHitView;
            }
        }

        return hitView;
    }
}

- ( BOOL )isPassthroughView:( UIView *)view {

    if (view == nil ) {
        return NO ;
    }

    if ([ self .passthroughViews containsObject:view]) {
        return YES ;
    }

    return [ self isPassthroughView:view.superview];
}

-( void ) dealloc{
    self .passthroughViews = nil ;
}

@end

关键要理解 hitTest 方法的作用，可参考：

1. http://blog.sina.com.cn/s/blog_677089db01012wpg.html
2. https://github.com/werner77/WEPopover

本文链接 http://unmi.cc/uiview-event-passthrough/, 来自隔叶黄莺 Unmi Blog