Ios 当滚动视图移动时，Xamarin UIScrollView手势识别器应开始报告速度为0

我正在使用Xamarin开发一个iOS应用程序，我想对UIScrollView进行子类化，以便根据其速度处理滚动视图中的平移手势。因此，我覆盖了

手势识别器shouldBegin

，并检查了平移手势的

速度视图。这对于第一个手势很有效，但在滚动视图运动（减速）时触发的后续平移手势始终报告速度为（0，0）：

滚动时平移一次和第二次后的输出：

Pan gesture velocity: {X=37.92359, Y=-872.2426}
Pan gesture velocity: {X=0, Y=0}

这是一个bug还是预期的行为

编辑：交叉发布在Xamarin的论坛上：

编辑以澄清：

2015-10-26 12:07:06.676 iOSVelocity[68486:2309184] Touch-enabed Pan gesture velocity: {X=-608.4813, Y=0}
2015-10-26 12:07:06.703 iOSVelocity[68486:2309184] Touch-enabed Pan gesture velocity: {X=-1213.629, Y=0}
2015-10-26 12:07:06.726 iOSVelocity[68486:2309184] Touch-enabed Pan gesture velocity: {X=-935.5507, Y=0}
2015-10-26 12:07:06.771 iOSVelocity[68486:2309184] Touch-enabed Pan gesture velocity: {X=-1191.385, Y=-8.564461}
2015-10-26 12:07:06.772 iOSVelocity[68486:2309184] otherGestureRecognizer velocity: {X=-1191.385, Y=-8.564461}
2015-10-26 12:07:06.772 iOSVelocity[68486:2309184] otherGestureRecognizer velocity: {X=-1191.385, Y=-8.564461}
2015-10-26 12:07:08.882 iOSVelocity[68486:2309184] !!!! ShouldBegin velocity not reset !!!!
2015-10-26 12:07:08.885 iOSVelocity[68486:2309184] GestureRecognizerShouldBegin velocity: {X=-1191.385, Y=-8.564461}
2015-10-26 12:07:08.887 iOSVelocity[68486:2309184] otherGestureRecognizer velocity: {X=-1191.385, Y=-8.564461}
2015-10-26 12:07:08.889 iOSVelocity[68486:2309184] gestureRecognizer velocity: {X=0, Y=0}
2015-10-26 12:07:08.890 iOSVelocity[68486:2309184] otherGestureRecognizer velocity: {X=0, Y=0}
2015-10-26 12:07:08.891 iOSVelocity[68486:2309184] gestureRecognizer velocity: {X=0, Y=0}
2015-10-26 12:07:08.937 iOSVelocity[68486:2309184] otherGestureRecognizer velocity: {X=0, Y=0}
2015-10-26 12:07:08.938 iOSVelocity[68486:2309184] otherGestureRecognizer velocity: {X=0, Y=0}
2015-10-26 12:07:08.939 iOSVelocity[68486:2309184] gestureRecognizer velocity: {X=-336.9197, Y=0}
2015-10-26 12:07:08.940 iOSVelocity[68486:2309184] Touch-enabled Pan gesture velocity: {X=-336.9197, Y=0}
2015-10-26 12:07:08.954 iOSVelocity[68486:2309184] Touch-enabled Pan gesture velocity: {X=-650.7258, Y=0}
2015-10-26 12:07:08.961 iOSVelocity[68486:2309184] Touch-enabled Pan gesture velocity: {X=-650.7258, Y=0}
2015-10-26 12:07:08.993 iOSVelocity[68486:2309184] Touch-enabled Pan gesture velocity: {X=-914.0547, Y=0}
2015-10-26 12:07:09.027 iOSVelocity[68486:2309184] Touch-enabled Pan gesture velocity: {X=-734.1516, Y=0}
2015-10-26 12:07:09.032 iOSVelocity[68486:2309184] otherGestureRecognizer velocity: {X=-734.1516, Y=0}
2015-10-26 12:07:09.033 iOSVelocity[68486:2309184] otherGestureRecognizer velocity: {X=-734.1516, Y=0}
2015-10-26 12:07:09.060 iOSVelocity[68486:2309184] Touch-enabled Pan gesture velocity: {X=-1086.368, Y=0}

为了阐明我最终要做的事情：我在水平分页视图中有一个垂直滚动视图。我想检查平移的速度，以便在平移为“水平”（即X速度>Y速度）时告诉滚动视图不要处理该手势。默认行为是，一旦滚动视图处于运动状态，另一个手势仍会滚动，但这使得用户很难水平（跨页面）滚动，直到垂直滚动完全固定

这是一个bug还是预期的行为

就通过GestureRecognitizer上的VelocityInView获取p/s而言，至少根据我的经验，在平移运动开始后，但未停止/重置，应获得0,0。Obj-C/Swift将返回相同的内容，不要问我为什么，必须让实际的iOS开发人员询问原因

如果您真的需要在
gestureRecognitizer中开始
在您的UIScrollView子类中从任何其他pan识别器中分配一个私有CGPoint，那么在其他任何地方都可以获得velocity，您应该是黄金级的

示例输出：

2015-10-26 12:07:06.676 iOSVelocity[68486:2309184] Touch-enabed Pan gesture velocity: {X=-608.4813, Y=0}
2015-10-26 12:07:06.703 iOSVelocity[68486:2309184] Touch-enabed Pan gesture velocity: {X=-1213.629, Y=0}
2015-10-26 12:07:06.726 iOSVelocity[68486:2309184] Touch-enabed Pan gesture velocity: {X=-935.5507, Y=0}
2015-10-26 12:07:06.771 iOSVelocity[68486:2309184] Touch-enabed Pan gesture velocity: {X=-1191.385, Y=-8.564461}
2015-10-26 12:07:06.772 iOSVelocity[68486:2309184] otherGestureRecognizer velocity: {X=-1191.385, Y=-8.564461}
2015-10-26 12:07:06.772 iOSVelocity[68486:2309184] otherGestureRecognizer velocity: {X=-1191.385, Y=-8.564461}
2015-10-26 12:07:08.882 iOSVelocity[68486:2309184] !!!! ShouldBegin velocity not reset !!!!
2015-10-26 12:07:08.885 iOSVelocity[68486:2309184] GestureRecognizerShouldBegin velocity: {X=-1191.385, Y=-8.564461}
2015-10-26 12:07:08.887 iOSVelocity[68486:2309184] otherGestureRecognizer velocity: {X=-1191.385, Y=-8.564461}
2015-10-26 12:07:08.889 iOSVelocity[68486:2309184] gestureRecognizer velocity: {X=0, Y=0}
2015-10-26 12:07:08.890 iOSVelocity[68486:2309184] otherGestureRecognizer velocity: {X=0, Y=0}
2015-10-26 12:07:08.891 iOSVelocity[68486:2309184] gestureRecognizer velocity: {X=0, Y=0}
2015-10-26 12:07:08.937 iOSVelocity[68486:2309184] otherGestureRecognizer velocity: {X=0, Y=0}
2015-10-26 12:07:08.938 iOSVelocity[68486:2309184] otherGestureRecognizer velocity: {X=0, Y=0}
2015-10-26 12:07:08.939 iOSVelocity[68486:2309184] gestureRecognizer velocity: {X=-336.9197, Y=0}
2015-10-26 12:07:08.940 iOSVelocity[68486:2309184] Touch-enabled Pan gesture velocity: {X=-336.9197, Y=0}
2015-10-26 12:07:08.954 iOSVelocity[68486:2309184] Touch-enabled Pan gesture velocity: {X=-650.7258, Y=0}
2015-10-26 12:07:08.961 iOSVelocity[68486:2309184] Touch-enabled Pan gesture velocity: {X=-650.7258, Y=0}
2015-10-26 12:07:08.993 iOSVelocity[68486:2309184] Touch-enabled Pan gesture velocity: {X=-914.0547, Y=0}
2015-10-26 12:07:09.027 iOSVelocity[68486:2309184] Touch-enabled Pan gesture velocity: {X=-734.1516, Y=0}
2015-10-26 12:07:09.032 iOSVelocity[68486:2309184] otherGestureRecognizer velocity: {X=-734.1516, Y=0}
2015-10-26 12:07:09.033 iOSVelocity[68486:2309184] otherGestureRecognizer velocity: {X=-734.1516, Y=0}
2015-10-26 12:07:09.060 iOSVelocity[68486:2309184] Touch-enabled Pan gesture velocity: {X=-1086.368, Y=0}

UIScrollView子类示例：

2015-10-26 12:07:06.676 iOSVelocity[68486:2309184] Touch-enabed Pan gesture velocity: {X=-608.4813, Y=0}
2015-10-26 12:07:06.703 iOSVelocity[68486:2309184] Touch-enabed Pan gesture velocity: {X=-1213.629, Y=0}
2015-10-26 12:07:06.726 iOSVelocity[68486:2309184] Touch-enabed Pan gesture velocity: {X=-935.5507, Y=0}
2015-10-26 12:07:06.771 iOSVelocity[68486:2309184] Touch-enabed Pan gesture velocity: {X=-1191.385, Y=-8.564461}
2015-10-26 12:07:06.772 iOSVelocity[68486:2309184] otherGestureRecognizer velocity: {X=-1191.385, Y=-8.564461}
2015-10-26 12:07:06.772 iOSVelocity[68486:2309184] otherGestureRecognizer velocity: {X=-1191.385, Y=-8.564461}
2015-10-26 12:07:08.882 iOSVelocity[68486:2309184] !!!! ShouldBegin velocity not reset !!!!
2015-10-26 12:07:08.885 iOSVelocity[68486:2309184] GestureRecognizerShouldBegin velocity: {X=-1191.385, Y=-8.564461}
2015-10-26 12:07:08.887 iOSVelocity[68486:2309184] otherGestureRecognizer velocity: {X=-1191.385, Y=-8.564461}
2015-10-26 12:07:08.889 iOSVelocity[68486:2309184] gestureRecognizer velocity: {X=0, Y=0}
2015-10-26 12:07:08.890 iOSVelocity[68486:2309184] otherGestureRecognizer velocity: {X=0, Y=0}
2015-10-26 12:07:08.891 iOSVelocity[68486:2309184] gestureRecognizer velocity: {X=0, Y=0}
2015-10-26 12:07:08.937 iOSVelocity[68486:2309184] otherGestureRecognizer velocity: {X=0, Y=0}
2015-10-26 12:07:08.938 iOSVelocity[68486:2309184] otherGestureRecognizer velocity: {X=0, Y=0}
2015-10-26 12:07:08.939 iOSVelocity[68486:2309184] gestureRecognizer velocity: {X=-336.9197, Y=0}
2015-10-26 12:07:08.940 iOSVelocity[68486:2309184] Touch-enabled Pan gesture velocity: {X=-336.9197, Y=0}
2015-10-26 12:07:08.954 iOSVelocity[68486:2309184] Touch-enabled Pan gesture velocity: {X=-650.7258, Y=0}
2015-10-26 12:07:08.961 iOSVelocity[68486:2309184] Touch-enabled Pan gesture velocity: {X=-650.7258, Y=0}
2015-10-26 12:07:08.993 iOSVelocity[68486:2309184] Touch-enabled Pan gesture velocity: {X=-914.0547, Y=0}
2015-10-26 12:07:09.027 iOSVelocity[68486:2309184] Touch-enabled Pan gesture velocity: {X=-734.1516, Y=0}
2015-10-26 12:07:09.032 iOSVelocity[68486:2309184] otherGestureRecognizer velocity: {X=-734.1516, Y=0}
2015-10-26 12:07:09.033 iOSVelocity[68486:2309184] otherGestureRecognizer velocity: {X=-734.1516, Y=0}
2015-10-26 12:07:09.060 iOSVelocity[68486:2309184] Touch-enabled Pan gesture velocity: {X=-1086.368, Y=0}

注意：这将使用
应与手势识别器同时识别
，以便在用户提起触摸后继续自动平移

注2：不确定是否捕获了所有手势状态排列，因此根据需要进行调整

我终于明白了。感谢@RobertN的帮助：）

关键在于，滚动视图使用的默认平移手势识别器如果已经处于运动状态，则始终报告0速度（例如，前一个手势的惯性仍然有效）。添加新的
UIPangestureRecognitizer
是记录后续手势的“实际”速度的好方法，但到那时，影响原始平移手势的
手势识别器就太晚了。因此，我所要做的就是添加一个
ShouldBegin
委托给我的新
UIPangestureRecognitizer
，并使用该委托返回
false
，以防我希望手势“掉到”父页面

        public MyScroll() : base()
        {
            UIPanGestureRecognizer panGesture = new UIPanGestureRecognizer();

            panGesture.ShouldBegin = delegate(UIGestureRecognizer recognizer)
            {
                CGPoint v = panGesture.VelocityInView(this);

                if (v.X != 0 || v.Y != 0)
                {
                    if (Math.Abs(v.X) > Math.Abs(v.Y))
                    {
                        return false;
                    }
                }

                return true;
            };

            this.AddGestureRecognizer(panGesture);
        }

这样，我就可以让默认的滚动视图平移手势识别器完成它的工作，而我的新
uipangestureerecognizer
可以识别用户何时做出一个新的水平手势，并将该手势传递给用户，以便寻呼机可以翻页。这使得父分页器和垂直页面滚动视图的组合可以很好地协同工作（想象一下，即使垂直页面处于运动状态，也可以垂直滚动页面并能够在页面间翻转）。注意，您还需要实现以下方法以允许两个手势识别器同时操作：

        [Export("gestureRecognizer:shouldRecognizeSimultaneouslyWithGestureRecognizer:")]
        public bool ShouldRecognizeSimultaneously(UIGestureRecognizer gestureRecognizer, UIGestureRecognizer otherGestureRecognizer)
        {
            return true;
        }

我尝试了这一点，但似乎发生的是，当您第二次做手势（移动时），默认的平移手势识别器（报告0）调用
GestureRecognitizerShouldBegin
，然后使用的速度是“新”平移手势识别器最后报告的速度。换言之，新的平移手势保留了前一个手势的过时值，因此在“常规”平移手势失败时（报告0），新的平移手势尚未“开始”并更新其值。我不知道如何让自定义的方法启动
ShouldBegin
方法…我刚刚还尝试从滚动视图中删除默认的平移手势识别器，只剩下新的平移手势识别器。我看到它进入“开始”状态的消息，但只有将该手势指定给滚动视图时，滚动视图才不会触发
手势识别器shouldBegin
方法，也不会再移动。将这个手势“连接”到我认为的视图是错误的。我不认为我做了什么特别的事情，这是整个UIScrollView子类，我将它放在一个视图（AddSubView）上，并添加了一个非常大的图像（UIImage通过UIImageView）以便可以平移。现在，我通常不会再和velocitys打交道了…，当用户的体验改变时，他们似乎总是皱起眉头。。。关于使用手势识别器，您的用例是什么？也许还有另一种方法可以做你需要的（？）来澄清我最终要做的事情：我在水平分页视图中有一个垂直滚动视图。我想检查平移的速度，以便在平移为“水平”（即X速度>Y速度）时告诉滚动视图不要处理该手势。默认行为是，一旦滚动视图处于运动状态，另一个手势仍会滚动，但这使得用户很难水平滚动（跨页面），直到垂直滚动完全固定。我准确地复制了您的代码，只是它提供了一个“旧”速度。仅将日志输出保留在
手势识别器shouldBegin
方法中，然后向下滚动然后向上滚动。您会注意到，初始平移的Y速度为负（向下）：
gestureRecognitizerShouldBegin速度：{X=73.03223，Y=-985.935}
，然后第二个手势显示其位置的“零格”