iOS WebCore的WebEvent和EventHandler

WebEvent是iOS专有的类，负责封装和携带从UIKit得到的系统事件信息，并由WebKit层的WAKResponder子类传递到WebCore的EventHandler。

UIKit层的逻辑可参考《iOS私有API（三） UIWebView下的手势识别器gestureRecognizer》，WebKit层的相关类可参考《WebCore::Widget浅探》。

开源码中WebEvent的声明为：

typedef enum {
    WebEventMouseDown,
    WebEventMouseUp,
    WebEventMouseMoved,

    WebEventScrollWheel,

    WebEventKeyDown,
    WebEventKeyUp,

    WebEventTouchBegin,
    WebEventTouchChange,
    WebEventTouchEnd,
    WebEventTouchCancel
} WebEventType;

typedef enum {
    WebEventTouchPhaseBegan,
    WebEventTouchPhaseMoved,
    WebEventTouchPhaseStationary,
    WebEventTouchPhaseEnded,
    WebEventTouchPhaseCancelled
} WebEventTouchPhaseType;

// These enum values are copied directly from GSEvent for compatibility.
typedef enum
{
    WebEventFlagMaskAlphaShift = 0x00010000,
    WebEventFlagMaskShift      = 0x00020000,
    WebEventFlagMaskControl    = 0x00040000,
    WebEventFlagMaskAlternate  = 0x00080000,
    WebEventFlagMaskCommand    = 0x00100000,
} WebEventFlagValues;
typedef unsigned WebEventFlags;

// These enum values are copied directly from GSEvent for compatibility.
typedef enum
{
    WebEventCharacterSetASCII           = 0,
    WebEventCharacterSetSymbol          = 1,
    WebEventCharacterSetDingbats        = 2,
    WebEventCharacterSetUnicode         = 253,
    WebEventCharacterSetFunctionKeys    = 254,
} WebEventCharacterSet;

@interface WebEvent : NSObject {
@private
    WebEventType _type;
    CFTimeInterval _timestamp;

    CGPoint _locationInWindow;

    NSString *_characters;
    NSString *_charactersIgnoringModifiers;
    WebEventFlags _modifierFlags;
    BOOL _keyRepeating;
    BOOL _popupVariant;
    uint16_t _keyCode;
    BOOL _tabKey;
    WebEventCharacterSet _characterSet;

    float _deltaX;
    float _deltaY;

    unsigned _touchCount;
    NSArray *_touchLocations;
    NSArray *_touchIdentifiers;
    NSArray *_touchPhases;

    BOOL _isGesture;
    float _gestureScale;
    float _gestureRotation;
}

- (WebEvent *)initWithMouseEventType:(WebEventType)type
                           timeStamp:(CFTimeInterval)timeStamp
                            location:(CGPoint)point;

- (WebEvent *)initWithScrollWheelEventWithTimeStamp:(CFTimeInterval)timeStamp
                                           location:(CGPoint)point
                                              deltaX:(float)deltaX
                                              deltaY:(float)deltaY;

- (WebEvent *)initWithTouchEventType:(WebEventType)type
                           timeStamp:(CFTimeInterval)timeStamp
                            location:(CGPoint)point
                           modifiers:(WebEventFlags)modifiers
                          touchCount:(unsigned)touchCount
                      touchLocations:(NSArray *)touchLocations
                    touchIdentifiers:(NSArray *)touchIdentifiers
                         touchPhases:(NSArray *)touchPhases isGesture:(BOOL)isGesture
                        gestureScale:(float)gestureScale
                     gestureRotation:(float)gestureRotation;

- (WebEvent *)initWithKeyEventType:(WebEventType)type
                         timeStamp:(CFTimeInterval)timeStamp
                        characters:(NSString *)characters
       charactersIgnoringModifiers:(NSString *)charactersIgnoringModifiers
                         modifiers:(WebEventFlags)modifiers
                       isRepeating:(BOOL)repeating
                    isPopupVariant:(BOOL)popupVariant
                           keyCode:(uint16_t)keyCode
                          isTabKey:(BOOL)tabKey
                      characterSet:(WebEventCharacterSet)characterSet;

@property(nonatomic,readonly) WebEventType type;
@property(nonatomic,readonly) CFTimeInterval timestamp;

// Mouse
@property(nonatomic,readonly) CGPoint locationInWindow;

// Keyboard
@property(nonatomic,readonly,retain) NSString *characters;
@property(nonatomic,readonly,retain) NSString *charactersIgnoringModifiers;
@property(nonatomic,readonly) WebEventFlags modifierFlags;
@property(nonatomic,readonly,getter=isKeyRepeating) BOOL keyRepeating;
@property(nonatomic,readonly,getter=isPopupVariant) BOOL popupVariant;
@property(nonatomic,readonly) uint16_t keyCode;
@property(nonatomic,readonly,getter=isTabKey) BOOL tabKey;
@property(nonatomic,readonly) WebEventCharacterSet characterSet;

// Scroll Wheel
@property(nonatomic,readonly) float deltaX;
@property(nonatomic,readonly) float deltaY;

// Touch
@property(nonatomic,readonly) unsigned touchCount;
@property(nonatomic,readonly,retain) NSArray *touchLocations;
@property(nonatomic,readonly,retain) NSArray *touchIdentifiers;
@property(nonatomic,readonly,retain) NSArray *touchPhases;

// Gesture
@property(nonatomic,readonly) BOOL isGesture;
@property(nonatomic,readonly) float gestureScale;
@property(nonatomic,readonly) float gestureRotation;
@end

WebEvent封装了4种事件：鼠标（手指）、键盘、滚轮、触摸，主要通过属性WebEventType type来区分。

鼠标事件主要由单击手势来触发，会产生mouseup，mousemove和mousedown事件。其中单击就是同一RunLoop内连贯的mousedown和mouseup，而mousemove是模拟事件，可触发mouseover消息。

键盘事件发生在编辑框内，按下iOS虚拟键盘的按键就会触发。

滚轮由双指平移手势触发，在输入框内有效。

触摸特指JavaScript监听的touchstart、gesturestart等消息，由UIWebTouchEventsGestureRecognizer来计算。

这些事件触发后，都会在主线程创建WebEvent，然后用GCD技术转到WebThread执行。

开源码的EventHandler.h中有如下几行：

#if PLATFORM(MAC) && defined(__OBJC__)
    void mouseDown(WebEvent *);
    void mouseUp(WebEvent *);
    void mouseMoved(WebEvent *);
    bool keyEvent(WebEvent *);
    bool wheelEvent(WebEvent *);

    void touchEvent(WebEvent *);

    static WebEvent *currentEvent();
#endif

使用xdb也能找到，可是在EventHandler的实现中却找不到，所以Apple是没有完全公开iOS源码的。

另有一个PlatformEventFactoryIOS.h的文件有如下声明：

class PlatformEventFactory {
public:
    static PlatformMouseEvent createPlatformMouseEvent(WebEvent *);
    static PlatformWheelEvent createPlatformWheelEvent(WebEvent *);
    static PlatformKeyboardEvent createPlatformKeyboardEvent(WebEvent *);
    static PlatformTouchEvent createPlatformTouchEvent(WebEvent *);
};

这些函数的作用就是把Objective-C类封装的WebEvent转换成WebCore里C++的PlatformEvent。可以猜测，接受WebEvent型参数的EventHandler函数也就只是简单做这个工作，转换后再直接调用通用的函数就ok了。如：

    bool handleMousePressEvent(const PlatformMouseEvent&);
    bool handleMouseMoveEvent(const PlatformMouseEvent&, HitTestResult* hoveredNode = 0, bool onlyUpdateScrollbars = false);
    bool handleMouseReleaseEvent(const PlatformMouseEvent&);
    bool handleWheelEvent(const PlatformWheelEvent&);
    void defaultWheelEventHandler(Node*, WheelEvent*);

#if ENABLE(GESTURE_EVENTS)
    bool handleGestureEvent(const PlatformGestureEvent&);
    bool handleGestureTap(const PlatformGestureEvent&, Node* preTargetedNode = 0);
    bool handleGestureScrollUpdate(const PlatformGestureEvent&);
#endif

一个堆栈示例：

Thread 4 WebThread, Queue : (null)
#0	0x03385790 in WebCore::EventHandler::mouseMoved(WebCore::PlatformMouseEvent const&) ()
#1	0x0338ae0f in WebCore::EventHandler::mouseMoved(WebEvent*) ()
#2	0x02efd822 in -[WebHTMLView(WebPrivate) mouseMoved:] ()
#3	0x03f6c6ac in -[WAKView _selfHandleEvent:] ()
#4	0x03f6c603 in -[WAKView handleEvent:] ()
#5	0x03f6f94d in -[WAKWindow sendEventSynchronously:] ()
#6	0x03f6f75b in __23-[WAKWindow sendEvent:]_block_invoke ()
#7	0x03f83fe2 in _WebThreadRun ()
#8	0x03f83ee0 in WebThreadRun ()
#9	0x03f6f71c in -[WAKWindow sendEvent:] ()
#10	0x03f6fa0c in __46-[WAKWindow sendMouseMoveEvent:contentChange:]_block_invoke ()
#11	0x03f83fe2 in _WebThreadRun ()
#12	0x03f83ee0 in WebThreadRun ()
#13	0x03f6f9d2 in -[WAKWindow sendMouseMoveEvent:contentChange:] ()
#14	0x0023609d in __64-[UIWebDocumentView(Interaction) _sendMouseMoveAndAttemptClick:]_block_invoke ()
#15	0x03f844ea in HandleRunSource ()
#16	0x0226e33f in __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ ()
#17	0x0226dd95 in __CFRunLoopDoSources0 ()
#18	0x0228b124 in __CFRunLoopRun ()
#19	0x0228a59f in CFRunLoopRunSpecific ()
#20	0x0228a3eb in CFRunLoopRunInMode ()
#21	0x03f83c30 in RunWebThread(void*) ()
#22	0x05a5c65c in _pthread_body ()
#23	0x05a5c4e6 in _pthread_start ()

其它的Event都差不多，不再赘述了。