objective-c - 自定义 UIGestureRecognizer : selector does not receive UIGestureRecognizerStateBegan

Question

我正在实现自定义 UIGestureRecognizer。为简单起见，假设它识别包含 >1 次触摸的手势。

这是 Gesture.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

这是一个选择器:

- (IBAction)handleGesture:(Gesture *)recognizer {
  printf("%s %d\n", __FUNCTION__, 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.

为什么选择器没有收到 UIGestureRecognizerStateBegan？

Answer 1

这对我来说不是特别明显，但规则似乎是:

• 通过 touchesBegan:... 发送给您的所有触摸随后都被视为属于您，除非您将状态设置为 UIGestureRecognizerStateFailed，UIGestureRecognizerStateEnded 或 UIGestureRecognizerStateCancelled;
• 如果您改为转换到 UIGestureRecognizerStateBegan，则手势识别器会将其发布，然后在现在分配的触摸时自动生成UIGestureRecognizerStateChanged给你搬家。

因此，您不应该为自己设置 UIGestureRecognizerStateChanged — 只需跟踪触摸并正确发布开始、结束、失败和取消即可。

在你的情况下，我认为你只需要删除 touchesMoved:... 中的状态集。

(另外:以上内容适用于 iOS 5 和 6；在 4 下，行为稍微更微妙。要在所有三个版本下工作，请使用类似 if(self.state == UIGestureRecognizerStateBegan) self.state 的结构= UIGestureRecognizerStateChanged; 当你知道你的属性已经改变时)