Objective c 自定义UIGestureRecognizer:选择器未接收UIGestureRecognizerStateStarted

我正在实现自定义UIgestureRecognitor。为简单起见，假设它识别由>1次触摸组成的手势

这是手势。m：

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

#define SHOW printf("%s %d %d %d\n", __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UIgestureRecognitzerStateStarted？

这对我来说不是特别明显，但规则似乎是：

• 通过

  touchsbegind:…

  发送给您的所有触摸随后被视为属于您，除非并直到您将状态设置为

  UIgestureRecognitizerStateFailed

  、

  UIgestureRecognitizerStateEnded

  或

  UIgestureRecognitizerStateCancelled

• 相反，如果您切换到

  UIgestureRecognitizerStateStarted

  ，则手势识别器将启用该状态，然后当现在分配给您的触摸移动时，自动生成

  UIgestureRecognitizerStateChanged

因此，您不应该为自己设置

UIgestureRecognitizerStateChanged

——只需跟踪触摸并正确张贴开始、结束、失败和取消

在您的情况下，我认为您只需要删除

touchsmoved:…

中的状态集

---

（旁白：上述情况适用于iOS 5和iOS 6；在iOS 4下，行为稍显微妙。要在所有三个版本下工作，请使用类似于

的结构，如果（self.state==uigestureRecognitizerStateStarted）self.state=uigestureRecognitizerStateChanged；

当您知道您的属性已更改时）

我刚刚检查过，是的，你完全正确：注释行“self.state=uigesturecognizerstatechanged；”解决了问题！非常感谢。

-[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.