版本記錄

前言

APP中的視圖就是進行人機交互的，各種點擊等手勢都是通過與屏幕視圖進行交互完成的。這里面很重要的一個就是HitTest方法，它用于尋找響應(yīng)者以及傳遞事件，接下來我們就一起研究下HitTest方法的調(diào)用機制。

hitTest方法

hitTest:withEvent:是UIView的一個方法，該方法會被系統(tǒng)調(diào)用，作用就是用于選擇最合適的視圖來響應(yīng)觸摸事件。

事件的聲明周期

每一個事件從產(chǎn)生到結(jié)束是有一個過程的，也就是事件的聲明周期。下面看一張圖。

幾個重要的類

1. UITouch

• 一個手指一次觸摸屏幕，就對應(yīng)生成一個UITouch對象。多個手指同時觸摸，生成多個UITouch對象。
• 多個手指先后觸摸，系統(tǒng)會根據(jù)觸摸的位置判斷是否更新同一個UITouch對象。若兩個手指一前一后觸摸同一個位置（即雙擊），那么第一次觸摸時生成一個UITouch對象，第二次觸摸更新這個UITouch對象（UITouch對象的 tap count 屬性值從1變成2）；若兩個手指一前一后觸摸的位置不同，將會生成兩個UITouch對象，兩者之間沒有聯(lián)系。
• 每個UITouch對象記錄了觸摸的一些信息，包括觸摸時間、位置、階段、所處的視圖、窗口等信息。
• 手指離開屏幕一段時間后，確定該UITouch對象不會再被更新將被釋放。

/#import <Foundation/Foundation.h>
#import <CoreGraphics/CoreGraphics.h>
#import <UIKit/UIKitDefines.h>

NS_ASSUME_NONNULL_BEGIN

@class UIWindow, UIView, UIGestureRecognizer;

typedef NS_ENUM(NSInteger, UITouchPhase) {
    UITouchPhaseBegan,             // whenever a finger touches the surface.
    UITouchPhaseMoved,             // whenever a finger moves on the surface.
    UITouchPhaseStationary,        // whenever a finger is touching the surface but hasn't moved since the previous event.
    UITouchPhaseEnded,             // whenever a finger leaves the surface.
    UITouchPhaseCancelled,         // whenever a touch doesn't end but we need to stop tracking (e.g. putting device to face)
};

typedef NS_ENUM(NSInteger, UIForceTouchCapability) {
    UIForceTouchCapabilityUnknown = 0,
    UIForceTouchCapabilityUnavailable = 1,
    UIForceTouchCapabilityAvailable = 2
};

typedef NS_ENUM(NSInteger, UITouchType) {
    UITouchTypeDirect,                       // A direct touch from a finger (on a screen)
    UITouchTypeIndirect,                     // An indirect touch (not a screen)
    UITouchTypeStylus NS_AVAILABLE_IOS(9_1), // A touch from a stylus
} NS_ENUM_AVAILABLE_IOS(9_0);

typedef NS_OPTIONS(NSInteger, UITouchProperties) {
    UITouchPropertyForce = (1UL << 0),
    UITouchPropertyAzimuth = (1UL << 1),
    UITouchPropertyAltitude = (1UL << 2),
    UITouchPropertyLocation = (1UL << 3), // For predicted Touches
} NS_AVAILABLE_IOS(9_1);

NS_CLASS_AVAILABLE_IOS(2_0) @interface UITouch : NSObject

@property(nonatomic,readonly) NSTimeInterval      timestamp;
@property(nonatomic,readonly) UITouchPhase        phase;
@property(nonatomic,readonly) NSUInteger          tapCount;   // touch down within a certain point within a certain amount of time
@property(nonatomic,readonly) UITouchType         type NS_AVAILABLE_IOS(9_0);

// majorRadius and majorRadiusTolerance are in points
// The majorRadius will be accurate +/- the majorRadiusTolerance
@property(nonatomic,readonly) CGFloat majorRadius NS_AVAILABLE_IOS(8_0);
@property(nonatomic,readonly) CGFloat majorRadiusTolerance NS_AVAILABLE_IOS(8_0);

@property(nullable,nonatomic,readonly,strong) UIWindow                        *window;
@property(nullable,nonatomic,readonly,strong) UIView                          *view;
@property(nullable,nonatomic,readonly,copy)   NSArray <UIGestureRecognizer *> *gestureRecognizers NS_AVAILABLE_IOS(3_2);

- (CGPoint)locationInView:(nullable UIView *)view;
- (CGPoint)previousLocationInView:(nullable UIView *)view;

// Use these methods to gain additional precision that may be available from touches.
// Do not use precise locations for hit testing. A touch may hit test inside a view, yet have a precise location that lies just outside.
- (CGPoint)preciseLocationInView:(nullable UIView *)view NS_AVAILABLE_IOS(9_1);
- (CGPoint)precisePreviousLocationInView:(nullable UIView *)view NS_AVAILABLE_IOS(9_1);

// Force of the touch, where 1.0 represents the force of an average touch
@property(nonatomic,readonly) CGFloat force NS_AVAILABLE_IOS(9_0);
// Maximum possible force with this input mechanism
@property(nonatomic,readonly) CGFloat maximumPossibleForce NS_AVAILABLE_IOS(9_0);

// Azimuth angle. Valid only for stylus touch types. Zero radians points along the positive X axis.
// Passing a nil for the view parameter will return the azimuth relative to the touch's window.
- (CGFloat)azimuthAngleInView:(nullable UIView *)view NS_AVAILABLE_IOS(9_1);
// A unit vector that points in the direction of the azimuth angle. Valid only for stylus touch types.
// Passing nil for the view parameter will return a unit vector relative to the touch's window.
- (CGVector)azimuthUnitVectorInView:(nullable UIView *)view NS_AVAILABLE_IOS(9_1);

// Altitude angle. Valid only for stylus touch types.
// Zero radians indicates that the stylus is parallel to the screen surface,
// while M_PI/2 radians indicates that it is normal to the screen surface.
@property(nonatomic,readonly) CGFloat altitudeAngle NS_AVAILABLE_IOS(9_1);

// An index which allows you to correlate updates with the original touch.
// Is only guaranteed non-nil if this UITouch expects or is an update.
@property(nonatomic,readonly) NSNumber * _Nullable estimationUpdateIndex NS_AVAILABLE_IOS(9_1);
// A set of properties that has estimated values
// Only denoting properties that are currently estimated
@property(nonatomic,readonly) UITouchProperties estimatedProperties NS_AVAILABLE_IOS(9_1);
// A set of properties that expect to have incoming updates in the future.
// If no updates are expected for an estimated property the current value is our final estimate.
// This happens e.g. for azimuth/altitude values when entering from the edges
@property(nonatomic,readonly) UITouchProperties estimatedPropertiesExpectingUpdates NS_AVAILABLE_IOS(9_1);


@end

NS_ASSUME_NONNULL_END

2. UIEvent

這個是事件的真身。觸摸的目的就是生成觸摸事件供響應(yīng)者響應(yīng)，一個觸摸事件對應(yīng)一個UIEvent對象，其中的type屬性標(biāo)識了事件的類型。如果一個觸摸事件可能是由多個手指同時觸摸產(chǎn)生的，觸摸對象集合通過allTouches屬性獲取。

#import <Foundation/Foundation.h>
#import <CoreGraphics/CoreGraphics.h>
#import <UIKit/UIKitDefines.h>

NS_ASSUME_NONNULL_BEGIN

@class UIWindow, UIView, UIGestureRecognizer, UITouch;

typedef NS_ENUM(NSInteger, UIEventType) {
    UIEventTypeTouches,
    UIEventTypeMotion,
    UIEventTypeRemoteControl,
    UIEventTypePresses NS_ENUM_AVAILABLE_IOS(9_0),
};

typedef NS_ENUM(NSInteger, UIEventSubtype) {
    // available in iPhone OS 3.0
    UIEventSubtypeNone                              = 0,
    
    // for UIEventTypeMotion, available in iPhone OS 3.0
    UIEventSubtypeMotionShake                       = 1,
    
    // for UIEventTypeRemoteControl, available in iOS 4.0
    UIEventSubtypeRemoteControlPlay                 = 100,
    UIEventSubtypeRemoteControlPause                = 101,
    UIEventSubtypeRemoteControlStop                 = 102,
    UIEventSubtypeRemoteControlTogglePlayPause      = 103,
    UIEventSubtypeRemoteControlNextTrack            = 104,
    UIEventSubtypeRemoteControlPreviousTrack        = 105,
    UIEventSubtypeRemoteControlBeginSeekingBackward = 106,
    UIEventSubtypeRemoteControlEndSeekingBackward   = 107,
    UIEventSubtypeRemoteControlBeginSeekingForward  = 108,
    UIEventSubtypeRemoteControlEndSeekingForward    = 109,
};


NS_CLASS_AVAILABLE_IOS(2_0) @interface UIEvent : NSObject

@property(nonatomic,readonly) UIEventType     type NS_AVAILABLE_IOS(3_0);
@property(nonatomic,readonly) UIEventSubtype  subtype NS_AVAILABLE_IOS(3_0);

@property(nonatomic,readonly) NSTimeInterval  timestamp;

#if UIKIT_DEFINE_AS_PROPERTIES
@property(nonatomic, readonly, nullable) NSSet <UITouch *> *allTouches;
#else
- (nullable NSSet <UITouch *> *)allTouches;
#endif
- (nullable NSSet <UITouch *> *)touchesForWindow:(UIWindow *)window;
- (nullable NSSet <UITouch *> *)touchesForView:(UIView *)view;
- (nullable NSSet <UITouch *> *)touchesForGestureRecognizer:(UIGestureRecognizer *)gesture NS_AVAILABLE_IOS(3_2);

// An array of auxiliary UITouch’s for the touch events that did not get delivered for a given main touch. This also includes an auxiliary version of the main touch itself.
- (nullable NSArray <UITouch *> *)coalescedTouchesForTouch:(UITouch *)touch NS_AVAILABLE_IOS(9_0);

// An array of auxiliary UITouch’s for touch events that are predicted to occur for a given main touch. These predictions may not exactly match the real behavior of the touch as it moves, so they should be interpreted as an estimate.
- (nullable NSArray <UITouch *> *)predictedTouchesForTouch:(UITouch *)touch NS_AVAILABLE_IOS(9_0);

@end

NS_ASSUME_NONNULL_END

3. UIReponder

先看一下API

#import <Foundation/Foundation.h>
#import <UIKit/UIKitDefines.h>
#import <UIKit/UIEvent.h>
#import <UIKit/UIPasteConfigurationSupporting.h>

NS_ASSUME_NONNULL_BEGIN

@class UIPress;
@class UIPressesEvent;

@protocol UIResponderStandardEditActions <NSObject>
@optional
- (void)cut:(nullable id)sender NS_AVAILABLE_IOS(3_0);
- (void)copy:(nullable id)sender NS_AVAILABLE_IOS(3_0);
- (void)paste:(nullable id)sender NS_AVAILABLE_IOS(3_0);
- (void)select:(nullable id)sender NS_AVAILABLE_IOS(3_0);
- (void)selectAll:(nullable id)sender NS_AVAILABLE_IOS(3_0);
- (void)delete:(nullable id)sender NS_AVAILABLE_IOS(3_2);
- (void)makeTextWritingDirectionLeftToRight:(nullable id)sender NS_AVAILABLE_IOS(5_0);
- (void)makeTextWritingDirectionRightToLeft:(nullable id)sender NS_AVAILABLE_IOS(5_0);
- (void)toggleBoldface:(nullable id)sender NS_AVAILABLE_IOS(6_0);
- (void)toggleItalics:(nullable id)sender NS_AVAILABLE_IOS(6_0);
- (void)toggleUnderline:(nullable id)sender NS_AVAILABLE_IOS(6_0);

- (void)increaseSize:(nullable id)sender NS_AVAILABLE_IOS(7_0);
- (void)decreaseSize:(nullable id)sender NS_AVAILABLE_IOS(7_0);

@end

NS_CLASS_AVAILABLE_IOS(2_0) @interface UIResponder : NSObject <UIResponderStandardEditActions>

#if UIKIT_DEFINE_AS_PROPERTIES
@property(nonatomic, readonly, nullable) UIResponder *nextResponder;
#else
- (nullable UIResponder*)nextResponder;
#endif

#if UIKIT_DEFINE_AS_PROPERTIES
@property(nonatomic, readonly) BOOL canBecomeFirstResponder;    // default is NO
#else
- (BOOL)canBecomeFirstResponder;    // default is NO
#endif
- (BOOL)becomeFirstResponder;

#if UIKIT_DEFINE_AS_PROPERTIES
@property(nonatomic, readonly) BOOL canResignFirstResponder;    // default is YES
#else
- (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.
- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(nullable UIEvent *)event;
- (void)touchesMoved:(NSSet<UITouch *> *)touches withEvent:(nullable UIEvent *)event;
- (void)touchesEnded:(NSSet<UITouch *> *)touches withEvent:(nullable UIEvent *)event;
- (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);

- (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);

- (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);

@end

typedef NS_OPTIONS(NSInteger, UIKeyModifierFlags) {
    UIKeyModifierAlphaShift     = 1 << 16,  // This bit indicates CapsLock
    UIKeyModifierShift          = 1 << 17,
    UIKeyModifierControl        = 1 << 18,
    UIKeyModifierAlternate      = 1 << 19,
    UIKeyModifierCommand        = 1 << 20,
    UIKeyModifierNumericPad     = 1 << 21,
} NS_ENUM_AVAILABLE_IOS(7_0);

NS_CLASS_AVAILABLE_IOS(7_0) @interface UIKeyCommand : NSObject <NSCopying, NSSecureCoding>

- (instancetype)init NS_DESIGNATED_INITIALIZER;
- (nullable instancetype)initWithCoder:(NSCoder *)aDecoder NS_DESIGNATED_INITIALIZER;

@property (nullable,nonatomic,readonly) NSString *input;
@property (nonatomic,readonly) UIKeyModifierFlags modifierFlags;
@property (nullable,nonatomic,copy) NSString *discoverabilityTitle NS_AVAILABLE_IOS(9_0);

// The action for UIKeyCommands should accept a single (id)sender, as do the UIResponderStandardEditActions above

// Creates an key command that will _not_ be discoverable in the UI.
+ (UIKeyCommand *)keyCommandWithInput:(NSString *)input modifierFlags:(UIKeyModifierFlags)modifierFlags action:(SEL)action;

// Key Commands with a discoverabilityTitle _will_ be discoverable in the UI.
+ (UIKeyCommand *)keyCommandWithInput:(NSString *)input modifierFlags:(UIKeyModifierFlags)modifierFlags action:(SEL)action discoverabilityTitle:(NSString *)discoverabilityTitle NS_AVAILABLE_IOS(9_0);

@end

@interface UIResponder (UIResponderKeyCommands)
@property (nullable,nonatomic,readonly) NSArray<UIKeyCommand *> *keyCommands NS_AVAILABLE_IOS(7_0); // returns an array of UIKeyCommand objects<
@end

@class UIInputViewController;
@class UITextInputMode;
@class UITextInputAssistantItem;

@interface UIResponder (UIResponderInputViewAdditions)

// Called and presented when object becomes first responder.  Goes up the responder chain.
@property (nullable, nonatomic, readonly, strong) __kindof UIView *inputView NS_AVAILABLE_IOS(3_2);
@property (nullable, nonatomic, readonly, strong) __kindof UIView *inputAccessoryView NS_AVAILABLE_IOS(3_2);

/// This method is for clients that wish to put buttons on the Shortcuts Bar, shown on top of the keyboard.
/// You may modify the returned inputAssistantItem to add to or replace the existing items on the bar.
/// Modifications made to the returned UITextInputAssistantItem are reflected automatically.
/// This method should not be overriden. Goes up the responder chain.
@property (nonnull, nonatomic, readonly, strong) UITextInputAssistantItem *inputAssistantItem NS_AVAILABLE_IOS(9_0) __TVOS_PROHIBITED __WATCHOS_PROHIBITED;

// For viewController equivalents of -inputView and -inputAccessoryView
// Called and presented when object becomes first responder.  Goes up the responder chain.
@property (nullable, nonatomic, readonly, strong) UIInputViewController *inputViewController NS_AVAILABLE_IOS(8_0);
@property (nullable, nonatomic, readonly, strong) UIInputViewController *inputAccessoryViewController NS_AVAILABLE_IOS(8_0);

/* When queried, returns the current UITextInputMode, from which the keyboard language can be determined.
 * When overridden it should return a previously-queried UITextInputMode object, which will attempt to be
 * set inside that app, but not persistently affect the user's system-wide keyboard settings. */
@property (nullable, nonatomic, readonly, strong) UITextInputMode *textInputMode NS_AVAILABLE_IOS(7_0);
/* When the first responder changes and an identifier is queried, the system will establish a context to
 * track the textInputMode automatically. The system will save and restore the state of that context to
 * the user defaults via the app identifier. Use of -textInputMode above will supersede use of -textInputContextIdentifier. */
@property (nullable, nonatomic, readonly, strong) NSString *textInputContextIdentifier NS_AVAILABLE_IOS(7_0);
// This call is to remove stored app identifier state that is no longer needed.
+ (void)clearTextInputContextIdentifier:(NSString *)identifier NS_AVAILABLE_IOS(7_0);

// If called while object is first responder, reloads inputView, inputAccessoryView, and textInputMode.  Otherwise ignored.
- (void)reloadInputViews NS_AVAILABLE_IOS(3_2);

@end

// These are pre-defined constants for use with the input property of UIKeyCommand objects.
UIKIT_EXTERN NSString *const UIKeyInputUpArrow         NS_AVAILABLE_IOS(7_0);
UIKIT_EXTERN NSString *const UIKeyInputDownArrow       NS_AVAILABLE_IOS(7_0);
UIKIT_EXTERN NSString *const UIKeyInputLeftArrow       NS_AVAILABLE_IOS(7_0);
UIKIT_EXTERN NSString *const UIKeyInputRightArrow      NS_AVAILABLE_IOS(7_0);
UIKIT_EXTERN NSString *const UIKeyInputEscape          NS_AVAILABLE_IOS(7_0);

@interface UIResponder (ActivityContinuation)
@property (nullable, nonatomic, strong) NSUserActivity *userActivity NS_AVAILABLE_IOS(8_0);
- (void)updateUserActivityState:(NSUserActivity *)activity NS_AVAILABLE_IOS(8_0);
- (void)restoreUserActivityState:(NSUserActivity *)activity NS_AVAILABLE_IOS(8_0);
@end

#if TARGET_OS_IOS
@interface UIResponder (UIPasteConfigurationSupporting) <UIPasteConfigurationSupporting>
@end
#endif

NS_ASSUME_NONNULL_END

我們的UIView、UIViewController、UIApplication、AppDelegate等很多類都繼承它，所以就可以響應(yīng)事件。響應(yīng)事件主要靠下面的幾個方法。

//手指觸碰屏幕，觸摸開始
- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(nullable UIEvent *)event;

//手指在屏幕上移動
- (void)touchesMoved:(NSSet<UITouch *> *)touches withEvent:(nullable UIEvent *)event;

//手指離開屏幕，觸摸結(jié)束
- (void)touchesEnded:(NSSet<UITouch *> *)touches withEvent:(nullable UIEvent *)event;

//觸摸結(jié)束前，某個系統(tǒng)事件中斷了觸摸，例如電話呼入
- (void)touchesCancelled:(NSSet<UITouch *> *)touches withEvent:(nullable UIEvent *)event;

尋找合適響應(yīng)視圖的過程

尋找過程

touch->UIApplication->UIWindow->UIViewController.view->subViews->...->view

• 用戶點擊屏幕產(chǎn)生一個觸摸事件，加入到UIApplication管理的事件隊列中。
• UIApplication會從事件隊列中取出最早的事件進行分發(fā)處理，先發(fā)送事件給應(yīng)用程序的主窗口UIWindow。
• 主窗口會調(diào)用其hitTest:withEvent:方法在視圖(UIView)層次結(jié)構(gòu)中找到一個最合適的UIView來處理觸摸事件。

這里需要說明的是，在尋找響應(yīng)UIView過程中大致的原理。

- (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event 
{
    //系統(tǒng)默認會忽略isUserInteractionEnabled設(shè)置為NO、隱藏、alpha小于等于0.01的視圖
    if (!self.isUserInteractionEnabled || self.isHidden || self.alpha <= 0.01) {
        return nil;
    }
    if ([self pointInside:point withEvent:event]) {
        for (UIView *subview in [self.subviews reverseObjectEnumerator]) {
            CGPoint convertedPoint = [subview convertPoint:point fromView:self];
            UIView *hitTestView = [subview hitTest:convertedPoint withEvent:event];
            if (hitTestView) {
                return hitTestView;
            }
        }
        return self;
    }
    return nil;
}

1. 首先在當(dāng)前視圖hitTest方法中調(diào)用pointInside方法，判斷觸摸點是否在當(dāng)前視圖內(nèi)部。
2. 如果pointInside方法返回NO，當(dāng)hitTest方法返回的是nil，該視圖不處理該事件。
3. 如果pointInside方法返回YES，說明觸摸點在該視圖內(nèi)部，則從最上層的子視圖開始遍歷，為什么從最上層呢？因為subviews數(shù)組后添加的視圖就是在數(shù)組的末尾，遍歷當(dāng)前視圖的所有子視圖，調(diào)用hitTest方法，重復(fù)1 - 3 步驟。
4. 直到有的子視圖hitTest方法返回非空對象或者全部子視圖遍歷完畢，則結(jié)束該視圖的循環(huán)遍歷。若第一次有子視圖的hitTest方法返回非空對象，則當(dāng)前視圖的hitTest方法就返回此對象，處理結(jié)束；若所有子視圖的hitTest方法都返回nil，則當(dāng)前視圖的hitTest方法返回當(dāng)前視圖本身，最終由該對象處理觸摸事件。

下面我們就借用一個例子說明一下這個尋找的過程。這里例子是別人寫的，已經(jīng)進行了引用標(biāo)注，在下面列出來參考文章。

這里首先假設(shè)：ViewB在ViewC上層，ViewD在ViewE上層，即ViewB的addSubView：執(zhí)行在ViewC之后，ViewD的addSubView：執(zhí)行在ViewE之后。

當(dāng)我們點擊屏幕的時候，也就是ViewE的紅點，hitTest執(zhí)行順序如下所示：下面是pointInside為YES部分，X部分執(zhí)行pointInside為NO部分，最終hitTest返回ViewE。

• 首先調(diào)用A的hitTest方法，觸摸點在其內(nèi)部，pointInside返回YES，遍歷子視圖，按照先后順序調(diào)用B和C的hitTest方法，記住B在C的上層，首先調(diào)用。
• 執(zhí)行B的hitTest方法，觸摸點不在B的內(nèi)部，pointInside返回NO，hitTest返回nil。
• 執(zhí)行C的hitTest方法，觸摸點在C的內(nèi)部，pointInside返回YES，遍歷子視圖，依次調(diào)用D和E的hitTest方法。
• D執(zhí)行hitTest方法，觸摸點不在D的內(nèi)部，pointInside返回NO，hitTest方法返回nil
• E執(zhí)行hitTest方法，觸摸點在E的內(nèi)部，pointInside返回YES，E沒有子視圖了，則hitTest返回的就是E本身，這樣就找到了需要顯示的視圖。

事件的傳遞過程

事件的傳遞和上邊尋找響應(yīng)視圖的hitTest中pointInside返回YES的視圖的執(zhí)行順序是相反的，都是從最上層的視圖開始傳遞，一直到UIApplication，借用上面的例子就是E來響應(yīng)事件，E如果不處理，就會傳遞給下一個響應(yīng)者C，C如果也不處理，就會傳遞給A，A如果也不處理，則系統(tǒng)就會忽略該事件了。

下面就是官方文檔給出的響應(yīng)過程。

1. 響應(yīng)者對事件的操作方式

響應(yīng)者對于事件的攔截以及傳遞都是通過touchesBegan:withEvent:
方法控制的，該方法的默認實現(xiàn)是將事件沿著默認的響應(yīng)鏈往下傳遞。

響應(yīng)者對于接收到的事件有3種操作：

• 不攔截，這個是默認操作

  • 事件會自動沿著默認的響應(yīng)鏈往下傳遞

• 攔截，不再往下分發(fā)事件

  • 重寫touchesBegan:withEvent:進行事件處理，不調(diào)用父類的touchesBegan:withEvent:

• 攔截，繼續(xù)往下分發(fā)事件

  • 重寫touchesBegan:withEvent:進行事件處理，同時調(diào)用父類的touchesBegan:withEvent:將事件往下傳遞

2. 響應(yīng)鏈中的事件傳遞規(guī)則

每一個響應(yīng)者對象（UIResponder對象）都有一個nextResponder方法，用于獲取響應(yīng)鏈中當(dāng)前對象的下一個響應(yīng)者。因此，一旦事件的最佳響應(yīng)者確定了，這個事件所處的響應(yīng)鏈就確定了。

• UIView
  • 如果視圖是根控制器的根視圖，那么nextResponder就是根控制器對象；否則，其nextResponder為父視圖。
• UIViewController
  • 若控制器的視圖是window的根視圖，則其nextResponder為窗口對象；若控制器是從別的控制器present出來的，則其nextResponder為presenting view controller。
• UIWindow
  • nextResponder為UIApplication對象。
• UIApplication
  • 若當(dāng)前應(yīng)用的app delegate是一個UIResponder對象，且不是UIView、UIViewController或app本身，則UIApplication的nextResponder為app delegate。

下面看一張圖

responderChain

可以用以下方式打印一個響應(yīng)鏈中的每一個響應(yīng)對象，在最佳響應(yīng)者的touchBegin:withEvent:方法中調(diào)用即可（別忘了調(diào)用父類的方法）。

- (void)printResponderChain
{
      UIResponder *responder = self; 
      printf("%s",[NSStringFromClass([responder class]) UTF8String]); 
      while (responder.nextResponder) {
           responder = responder.nextResponder;
           printf(" --> %s",[NSStringFromClass([responder class]) UTF8String]); 
      }
}

3. 手勢識別器比UIResponder具有更高的事件響應(yīng)優(yōu)先級

手勢分為離散型手勢（discrete gestures）和持續(xù)型手勢（continuous gesture）。系統(tǒng)提供的離散型手勢包括點按手勢（UITapGestureRecognizer）和輕掃手勢（UISwipeGestureRecognizer ），其余均為持續(xù)型手勢。

兩者主要區(qū)別在于狀態(tài)變化過程：

• 離散型：

  • 識別成功：Possible —> Recognized
  • 識別失?。?code>Possible —> Failed

• 持續(xù)型：

  • 完整識別：Possible —> Began —> [Changed] —> Ended
  • 不完整識別：Possible —> Began —> [Changed] —> Cancel

Window在將事件傳遞給hit-tested view之前，會先將事件傳遞給相關(guān)的手勢識別器并由手勢識別器優(yōu)先識別。若手勢識別器成功識別了事件，就會取消hit-tested view對事件的響應(yīng)；若手勢識別器沒能識別事件，hit-tested view才完全接手事件的響應(yīng)權(quán)。也就是說手勢的優(yōu)先級要比UIResponder高。

在手勢的一個子類UIGestureRecognizerSubclass.h中，調(diào)用下面幾個方法來響應(yīng)事件。

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event;
- (void)touchesMoved:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event;
- (void)touchesEnded:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event;
- (void)touchesCancelled:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event;

參考文章

1. iOS-使用hitTest控制點擊事件的響應(yīng)對象
2. iOS觸摸事件全家桶
3. iOS觸摸事件詳解

后記

未完，待續(xù)~~~