objective-c – 自定义UIGestureRecognizer：选择器不接收UIGest

这是Gesture.m：

#import "Gesture.h"
#import <UIKit/UIGestureRecognizerSubclass.h>

#define SHOW printf("%s %d %d %dn",__FUNCTION__,self.state,touches.count,self.numberOfTouches)

@implementation Gesture

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
  SHOW;
  if (self.numberOfTouches==1) return;
  self.state = UIGestureRecognizerStateBegan;
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
  SHOW;
  if (self.numberOfTouches==1) return;
  self.state = UIGestureRecognizerStateChanged;
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
  SHOW;
  if (self.numberOfTouches==1) return;
  self.state = UIGestureRecognizerStateEnded;
}
@end

这是一个选择器：

- (IBAction)handleGesture:(Gesture *)recognizer {
  printf("%s %dn",recognizer.state);
}

这是一个输出：

-[Gesture touchesBegan:withEvent:] 0 1 1  // 1st touch began
-[Gesture touchesMoved:withEvent:] 0 1 1
-[Gesture touchesMoved:withEvent:] 0 1 1
-[Gesture touchesMoved:withEvent:] 0 1 1
-[Gesture touchesBegan:withEvent:] 0 1 2  // 2nd touch began
-[Gesture touchesMoved:withEvent:] 1 1 2  // Gesture.state==UIGestureRecognizerStateBegan but selector was not called
-[ViewController handleGesture:] 2        // UIGestureRecognizerStateChanged received.
-[Gesture touchesMoved:withEvent:] 2 2 2
-[ViewController handleGesture:] 2
-[Gesture touchesMoved:withEvent:] 2 2 2
-[ViewController handleGesture:] 2
-[Gesture touchesMoved:withEvent:] 2 2 2
-[ViewController handleGesture:] 3        // UIGestureRecognizerStateEnded received.

为什么选择器不接收UIGestureRecognizerStateBegan？