IOS 触摸事件有哪些【面试题详解】

今天爱分享给大家带来IOS 触摸事件有哪些【面试题详解】，希望能够帮助到大家。
UIEvent

iOS将触摸事件定义第一个手指开始触摸屏幕到最后一个手指离开屏幕为一个触摸事件。用类UIEvent表示。

UITouch

一个手指第一次点屏幕，会形成一个UITouch对象，知道离开销毁，表示触碰。UITouch对象能表明了当前手指触碰屏幕的位置，状态。状态分为开始触碰，移动和离开。

根据定义，UIEvent实际包括了多个UITouch对象。有几个手指触碰，就会有几个UITouch对象。代码定义如下:

typedef NS_ENUM(NSInteger, UIEventType) {
    UIEventTypeTouches,
    UIEventTypeMotion,
    UIEventTypeRemoteControl,
    UIEventTypePresses API_AVAILABLE(ios(9.0)),
};
@interface UIEvent : NSObject

@property(nonatomic,readonly) UIEventType     type API_AVAILABLE(ios(3.0));
@property(nonatomic,readonly) UIEventSubtype  subtype API_AVAILABLE(ios(3.0));

@property(nonatomic,readonly) NSTimeInterval  timestamp;

@property(nonatomic, readonly, nullable) NSSet  *allTouches;

- (nullable NSSet  *)touchesForWindow:(UIWindow *)window;
- (nullable NSSet  *)touchesForView:(UIView *)view;
- (nullable NSSet  *)touchesForGestureRecognizer:(UIGestureRecognizer *)gesture API_AVAILABLE(ios(3.2));

@end

其中UIEventType表明了事件类型，UIEvent表示了三大事件。
allTouches是该事件所有UITouch对象的集合。

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)
};

@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 API_AVAILABLE(ios(9.0));

// majorRadius and majorRadiusTolerance are in points
// The majorRadius will be accurate +/- the majorRadiusTolerance
@property(nonatomic,readonly) CGFloat majorRadius API_AVAILABLE(ios(8.0));
@property(nonatomic,readonly) CGFloat majorRadiusTolerance API_AVAILABLE(ios(8.0));

@property(nullable,nonatomic,readonly,strong) UIWindow                        *window;
@property(nullable,nonatomic,readonly,strong) UIView                          *view;
@property(nullable,nonatomic,readonly,copy)   NSArray  *gestureRecognizers API_AVAILABLE(ios(3.2));

UITouch中phase表明了手指移动的状态，包括 1.开始点击；2.移动；3.保持; 4.离开；5.被取消（手指没有离开屏幕，但是系统不再跟踪它了）

综上，UIEvent就是一组UITouch。每当该组中任何一个UITouch对象的phase发生变化，系统都会产生一条TouchMessage。也就是说每次用户手指的移动和变化，UITouch都会形成状态改变，系统变回会形成Touch message进行传递和派发。