我们的App与用户进行交互，基本上是依赖于各种各样的触发事件和运动事件。例如，用户点击界面上的按钮，我们需要触发一个按钮点击事件，并进行相应的处理，以给用户一个响应。UIView的三大职责之一就是处理触发事件和运动事件，一个视图是一个事件响应者，可以处理点击等触发事件，而这些触发事件和运动事件就是在UIResponder类中定义的。

一个UIResponder类为那些需要响应并处理事件的对象定义了一组接口。这些事件主要分为两类：触摸事件(touch events)和运动事件(motion events)。UIResponder类为这两类事件都定义了一组接口，这个我们将在下面详细介绍，并探讨一下。

在UIKit中，UIApplication、UIView、UIViewController这几个类都是直接继承自UIResponder类。因此UIKit中的视图、控件、视图控制器，以及我们自定义的视图及视图控制器都有响应事件的能力。这些对象通常被称为响应对象，或者是响应者(以下我们统一使用响应者)。

本文将详细介绍一个UIResponder类提供的基本功能。不过在此之前，我们先来了解一下事件响应链机制。

响应链
大多数事件的分发都是依赖响应链的。响应链是由一系列链接在一起的响应者组成的。一般情况下，一条响应链开始于第一响应者，结束于application对象。如果一个响应者不能处理事件，则会将事件沿着响应链传到下一响应者。

那这里就会有三个问题：

• 响应链是何时构建的
  1.系统是如何确定第一响应者的
  2.确定第一响应者后，系统又是按照什么样的顺序来传递事件的
  构建响应链
  3.我们都知道在一个App中，所有视图是按一定的结构层次组织起来的，即树状层次结构。除了根视图外，每个视图都有一个父视图；而每个视图都可以有0个或多个子视图。而在这个树状结构构建的同时，也构建了一条完整的事件响应链。

确定第一响应者
当用户触发某一事件(触摸事件或运动事件)后，UIKit会创建一个事件对象(UIEvent)，该对象包含一些处理事件所需要的信息。然后事件对象被放到一个事件队列中。这些事件按照先进先出的顺序来处理。当处理事件时，程序的UIApplication对象会从队列头部取出一个事件对象，将其分发出去。通常首先是将事件分发给程序的主window对象，对于触摸事件来讲，window对象会首先尝试将事件分发给触摸事件发生的那个视图上。这一视图通常被称为hit-test视图，而查找这一视图的过程就叫做hit-testing。

系统使用hit-testing来找到触摸事件下的视图，它检测一个触摸事件是否发生在相应视图对象的边界之内(即视图的frame属性，这也是为什么子视图如果在父视图的frame之外时，是无法响应事件的)。如果在，则会递归检测其所有的子视图。包含触摸点的视图层次架构中最底层的视图就是hit-test视图。在检测出hit-test视图后，系统就将事件发送给这个视图来进行处理。

我们通过一个示例来演示hit-testing的过程。图1是一个视图层次结构，

#if UIKIT_DEFINE_AS_PROPERTIES
@property(nonatomic, readonly, nullable) UIResponder *nextResponder;
#else
//上面提到在响应链中负责传递事件的方法是nextResponder，其声明如下
- (nullable UIResponder*)nextResponder;
#endif

#if UIKIT_DEFINE_AS_PROPERTIES

@property(nonatomic, readonly) BOOL canBecomeFirstResponder;    // default is NO
#else
//是否将目标对象设置为第一响应者的资格
- (BOOL)canBecomeFirstResponder;    // default is NO
#endif
//成为第一响应者
- (BOOL)becomeFirstResponder;

#if UIKIT_DEFINE_AS_PROPERTIES
@property(nonatomic, readonly) BOOL canResignFirstResponder;    // default is YES
#else
//是否将目标对象设置为失去第一响应者的资格
- (BOOL)canResignFirstResponder;    // default is YES
#endif
- (BOOL)resignFirstResponder;

#if UIKIT_DEFINE_AS_PROPERTIES
@property(nonatomic, readonly) BOOL isFirstResponder;
#else
- (BOOL)isFirstResponder;
#endif

// Generally, all responders which do custom touch handling should override all four of these methods.
// Your responder will receive either touchesEnded:withEvent: or touchesCancelled:withEvent: for each
// touch it is handling (those touches it received in touchesBegan:withEvent:).
// *** You must handle cancelled touches to ensure correct behavior in your application.  Failure to
// do so is very likely to lead to incorrect behavior or crashes.
#UIResponder内部提供了以下方法来处理事件触摸事件
// UIView是UIResponder的子类，可以覆盖下列4个方法处理不同的触摸事件
// 一根或者多根手指开始触摸view，系统会自动调用view的下面方法
- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(nullable UIEvent *)event;
// 一根或者多根手指在view上移动，系统会自动调用view的下面方法（随着手指的移动，会持续调用该方法）
- (void)touchesMoved:(NSSet<UITouch *> *)touches withEvent:(nullable UIEvent *)event;
// 触摸结束前，某个系统事件(例如电话呼入)会打断触摸过程，系统会自动调用view的下面方法
- (void)touchesEnded:(NSSet<UITouch *> *)touches withEvent:(nullable UIEvent *)event;
// 触摸结束前，某个系统事件(例如电话呼入)会打断触摸过程，系统会自动调用view的下面方法
- (void)touchesCancelled:(NSSet<UITouch *> *)touches withEvent:(nullable UIEvent *)event;

- (void)touchesEstimatedPropertiesUpdated:(NSSet<UITouch *> *)touches NS_AVAILABLE_IOS(9_1);

// Generally, all responders which do custom press handling should override all four of these methods.
// Your responder will receive either pressesEnded:withEvent or pressesCancelled:withEvent: for each
// press it is handling (those presses it received in pressesBegan:withEvent:).
// pressesChanged:withEvent: will be invoked for presses that provide an analog value
// (like thumbsticks or analog push buttons)
// *** You must handle cancelled presses to ensure correct behavior in your application.  Failure to
// do so is very likely to lead to incorrect behavior or crashes.
- (void)pressesBegan:(NSSet<UIPress *> *)presses withEvent:(nullable UIPressesEvent *)event NS_AVAILABLE_IOS(9_0);
- (void)pressesChanged:(NSSet<UIPress *> *)presses withEvent:(nullable UIPressesEvent *)event NS_AVAILABLE_IOS(9_0);
- (void)pressesEnded:(NSSet<UIPress *> *)presses withEvent:(nullable UIPressesEvent *)event NS_AVAILABLE_IOS(9_0);
- (void)pressesCancelled:(NSSet<UIPress *> *)presses withEvent:(nullable UIPressesEvent *)event NS_AVAILABLE_IOS(9_0);
//加速计事件
- (void)motionBegan:(UIEventSubtype)motion withEvent:(nullable UIEvent *)event NS_AVAILABLE_IOS(3_0);
- (void)motionEnded:(UIEventSubtype)motion withEvent:(nullable UIEvent *)event NS_AVAILABLE_IOS(3_0);
- (void)motionCancelled:(UIEventSubtype)motion withEvent:(nullable UIEvent *)event NS_AVAILABLE_IOS(3_0);
//远程控制事件
- (void)remoteControlReceivedWithEvent:(nullable UIEvent *)event NS_AVAILABLE_IOS(4_0);

- (BOOL)canPerformAction:(SEL)action withSender:(nullable id)sender NS_AVAILABLE_IOS(3_0);
// Allows an action to be forwarded to another target. By default checks -canPerformAction:withSender: to either return self, or go up the responder chain.
- (nullable id)targetForAction:(SEL)action withSender:(nullable id)sender NS_AVAILABLE_IOS(7_0);

@property(nullable, nonatomic,readonly) NSUndoManager *undoManager NS_AVAILABLE_IOS(3_0);

- (UIResponder *)nextResponder

- (BOOL)isFirstResponder

- (BOOL)becomeFirstResponder

- (BOOL)canBecomeFirstResponder

- (BOOL)resignFirstResponder
- (BOOL)canResignFirstResponder

@property(nonatomic, readonly, retain) UIView *inputView
@property(nonatomic, readonly, retain) UIInputViewController *inputViewController

@property(nonatomic, readonly, retain) UIView *inputAccessoryView
@property(nonatomic, readonly, retain) UIInputViewController *inputAccessoryViewController

- (void)reloadInputViews

// 当一个或多个手指触摸到一个视图或窗口
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
// 当与事件相关的一个或多个手指在视图或窗口上移动时
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
// 当一个或多个手指从视图或窗口上抬起时
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
// 当一个系统事件取消一个触摸事件时
- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event

// 移动事件开始
- (void)motionBegan:(UIEventSubtype)motion withEvent:(UIEvent *)event
// 移动事件结束
- (void)motionEnded:(UIEventSubtype)motion withEvent:(UIEvent *)event
// 取消移动事件
- (void)motionCancelled:(UIEventSubtype)motion withEvent:(UIEvent *)event

- (void)remoteControlReceivedWithEvent:(UIEvent *)event

- (BOOL)canPerformAction:(SEL)action withSender:(id)sender

- (id)targetForAction:(SEL)action withSender:(id)sender

- (id)targetForAction:(SEL)action withSender:(id)sender{    UIMenuController *menuController = [UIMenuController sharedMenuController]; 
if (action == @selector(selectAll:) || action == @selector(paste:) ||action == @selector(copy:) || action == @selector(cut:)) { 
if (menuController) {           

[UIMenuController sharedMenuController].menuVisible = NO;       

}       
return nil; 

}   
return [super targetForAction:action withSender:sender];

}

- (void)viewDidLoad {

    [super viewDidLoad];


    label=[[UILabel alloc]initWithFrame:CGRectMake(100, 100, SCREEN_WIDTH-200, 100)];

    label.text=@"开始你几十次那就瞌睡虫你桑蚕丝次数次时间长是程思佳传送才加上就程思佳测试才加上产品搜救出平时";

    label.numberOfLines=0;

    label.userInteractionEnabled = YES;

    [self.view addSubview:label];

    [label addGestureRecognizer:[[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(labelClick)]];


}
-(void)labelClick{
NSLog(@"测试");

    UIMenuController *menuController = [UIMenuController sharedMenuController];

    menuController.menuItems = @[ [[UIMenuItem alloc] initWithTitle:@"顶" action:@selector(ding:)], [[UIMenuItem alloc] initWithTitle:@"回复" action:@selector(reply:)], [[UIMenuItem alloc] initWithTitle:@"举报" action:@selector(warn:)] ];
// 菜单最终显示的位置

    [menuController setTargetRect:label.bounds inView:label];
// 显示菜单

    [menuController setMenuVisible:YES animated:YES];

}
//让Label具备成为第一响应者的资格（默认为NO），需手动开启
- (BOOL)canBecomeFirstResponder{
return YES;

}
-(void)ding:(id)send{
NSLog(@"ding");

}
-(void)reply:(id)send{
NSLog(@"reply");

}
-(void)warn:(id)send{
NSLog(@"warn");

}
////判断当前的方法，是否显示需要显示的项
//- (BOOL)canPerformAction:(SEL)action withSender:(id)sender{
//    if ( (action == @selector(copy:) && label.text)
//        ||(action == @selector(cut:) && label.text) || action == @selector(paste:) || action == @selector(ding:) || action == @selector(reply:) || action == @selector(warn:)){
//        return YES;
//    }
//    return NO;
//        
//}
//方法来获取可以响应某一行为的接收者：
- (id)targetForAction:(SEL)action withSender:(id)sender{    UIMenuController *menuController = [UIMenuController sharedMenuController];
if (action == @selector(selectAll:) || action == @selector(paste:) ||action == @selector(copy:) || action == @selector(cut:)) {
if (menuController) {

            [UIMenuController sharedMenuController].menuVisible = NO;

        }
return nil;

    }
return [super targetForAction:action withSender:sender];

}