UIView 中的控件事件穿透 Passthrough 的實現

我們在有多個 UIView 層疊時，比如一個按鈕被一個 UIView 遮蓋時，想要在點擊最上層的 UIView 時能觸發按鈕的相應事件，我們該如何實現呢，初步可以想到幾種辦法：

1. 把按鈕上層的所有 UIView 的 userInteractionEnabled 屬性設置爲 NO，要是 UIView 有自己的交互事件該如何辦呢？而且這個 userInteractionEnabled 不能動態設置，等到點擊後決定設置它的 NO 是沒用的

2. UIView 接受到點擊事件後主動去觸發下面按鈕的點擊，這時的關題有三，按鈕沒有點擊過程中的交換效果、多層 UIView 時不切實際，逐層下傳嗎、還有就是其他雙擊、三擊或別的手勢如何處理

我也一直被前面兩種方式糾纏着，同時也讓 UIPopoverController 的 NSArray *passthroughViews 屬性提醒着，因爲對於 UIPopoverController，設置到它的 passthoughViews 屬性中的控件事件可以完全從 UIDimmingView 下透出來。但苦於不可能看到 UIPopoverController 的源碼，還是後面一而再的 Google 終於發現了 UIView 的方法：

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

只要實現了最頂層的 UIView 的 hitTest 方法，在某些情況返回下層的某個按鈕實例，即相當於把那個按鈕的事件透出來了，比如在點擊落在該按鈕上時，不管這個按鈕在 UIView 下多少層都可以把它挖出來。

先看效果圖：

三個圖分別是：

1. 所見到的，按鈕被半透明紅色 View 遮住了一部分
2. 可點擊未遮住的按鈕部分，可看到按鈕被點下未擡起的效果
3. 在紅色的 View 中點擊按鈕被遮住部分，同樣觸發了按鈕的相應事件，且有中間效果，也就是說按鈕穿透出來了

再看代碼實現，有兩部分代碼，分別是 ViewController 和  CustomController

本文原始鏈接：http://unmi.cc/uiview-event-passthrough, 來自：隔葉黃鶯 Unmi Blog

ViewController.h

//
//  ViewController.h
 
//
//  Created by Unmi on 11/15/11.
//  Copyright (c) 2011 http://unmi.cc. All rights reserved.
//
 
#import <UIKit/UIKit.h>
 
@interfaceViewController : 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"
 
@implementationViewController{
    UIButton*passthroughButton;
}
 
#pragma mark - View lifecycle
 
- (void)viewDidLoad
{
    [superviewDidLoad];
 
    passthroughButton = [UIButtonbuttonWithType: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 = [UIColorcolorWithRed:1 green:0 blue:0 alpha:.5];
    customView.passthroughViews = [NSArrayarrayWithObject:passthroughButton];
    [self.view addSubview:customView];
    [customView release];
}
 
- (void)dealloc {
    [superdealloc];
}
@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>
 
@interfaceCustomView : 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"
 
@interfaceCustomView()
-(BOOL) isPassthroughView: (UIView*) view;
@end
 
@implementationCustomView{
    BOOLtestHits;
}
 
@synthesizepassthroughViews=_passthroughViews;
 
-(UIView*) hitTest:(CGPoint)point withEvent:(UIEvent*)event{
    if(testHits){
        returnnil;
    }
     
    if(!self.passthroughViews
        || (self.passthroughViews &&self.passthroughViews.count == 0)){
        returnself;
    }else {
         
        UIView*hitView = [superhitTest: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;
            }
        }
         
        returnhitView;
    }
}
 
- (BOOL)isPassthroughView:(UIView*)view {
     
    if(view == nil) {
        returnNO;
    }
     
    if([self.passthroughViews containsObject:view]) {
        returnYES;
    }
     
    return[self isPassthroughView:view.superview];
}             
 
-(void) dealloc{
    self.passthroughViews =nil;
}
 
@end

關鍵要理解 hitTest 方法的作用，可參考：

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