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。

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

有两部分代码，分别是 ViewController 和  CustomController

//
//  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.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
//  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
//
//  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