2019-7-15-win10-uwp-在笔迹开始书写拿到书写移动事件

title	author	date	CreateTime	categories
win10 uwp 在笔迹开始书写拿到书写移动事件	lindexi	2019-7-15 8:58:5 +0800	2019-05-22 10:42:22 +0800	Win10 UWP

在使用 InkCanvas 的过程，无法直接通过 Pointer 消息拿到书写移动，需要使用 StrokeInput 才能获取到

在 InkCanvas.InkPresenter.StrokeInput 提供了 StrokeStarted 、StrokeContinued 、StrokeEnded 这些看名字就知道是干什么用的事件，通过这些事件可以在书写的过程拿到触摸事件或鼠标事件

使用 StrokeContinued 作为例子，先在 XAML 界面放一个 InkCanvas 控件，同时修改他的属性名是 InkCanvas 在后台代码可以这样写

            InkCanvas.InkPresenter.StrokeInput.StrokeContinued += StrokeContinued;

拿到的StrokeContinued是PointerEventArgs可以拿到很多信息

        public void StrokeContinued(InkStrokeInput sender, PointerEventArgs args)
        {

        }

在 Win10 的 Anniversary Update 1607 提供了 CoreWetStrokeUpdateSource 可以在湿笔迹的时候触发事件

在 CoreWetStrokeUpdateSource 同样提供了开始书写和书写过程中的事件

先通过 Create 方法创建 CoreWetStrokeUpdateSource 请看代码

 var coreWetStrokeUpdateSource = CoreWetStrokeUpdateSource.Create(inkCanvas.InkPresenter);

这个事件有一点坑的是有加入的时机问题，请确保在所有的 InkCanvas 包括他的容器都 Loaded 完成之后才可以使用这个事件，不然是不会有触发的

通过 coreWetStrokeUpdateSource 可以拿到触摸按下和移动等事件

coreWetStrokeUpdateSource.WetStrokeStarting += CoreWetStrokeUpdateSource_WetStrokeStarting;
coreWetStrokeUpdateSource.WetStrokeContinuing += CoreWetStrokeUpdateSource_WetStrokeContinuing;
coreWetStrokeUpdateSource.WetStrokeStopping += CoreWetStrokeUpdateSource_WetStrokeStopping;
coreWetStrokeUpdateSource.WetStrokeCompleted += CoreWetStrokeUpdateSource_WetStrokeCompleted;

我在这些事件里面做输出，这样可以知道在多指触摸下的事件是如何触发的

        private void CoreWetStrokeUpdateSource_WetStrokeCompleted(CoreWetStrokeUpdateSource sender,
            CoreWetStrokeUpdateEventArgs args)
        {
            Debug.WriteLine($"CoreWetStrokeUpdateSource_WetStrokeCompleted{args.PointerId}");
        }

        private void CoreWetStrokeUpdateSource_WetStrokeStopping(CoreWetStrokeUpdateSource sender,
            CoreWetStrokeUpdateEventArgs args)
        {
            Debug.WriteLine($"WetStrokeStopping{args.PointerId}");
        }

        private void CoreWetStrokeUpdateSource_WetStrokeContinuing(CoreWetStrokeUpdateSource sender,
            CoreWetStrokeUpdateEventArgs args)
        {
            Debug.WriteLine($"CoreWetStrokeUpdateSource_WetStrokeContinuing {args.PointerId}");
        }

        private void CoreWetStrokeUpdateSource_WetStrokeStarting(CoreWetStrokeUpdateSource sender,
            CoreWetStrokeUpdateEventArgs args)
        {
            Debug.WriteLine($"CoreWetStrokeUpdateSource_WetStrokeStarting{args.PointerId}");
        }

运行代码可以看到下面的输出

CoreWetStrokeUpdateSource_WetStrokeStarting 1
CoreWetStrokeUpdateSource_WetStrokeContinuing 1
CoreWetStrokeUpdateSource_WetStrokeContinuing 1
……
CoreWetStrokeUpdateSource_WetStrokeStarting 2
CoreWetStrokeUpdateSource_WetStrokeStarting 3
CoreWetStrokeUpdateSource_WetStrokeContinuing 1
CoreWetStrokeUpdateSource_WetStrokeContinuing 2
CoreWetStrokeUpdateSource_WetStrokeContinuing 3
CoreWetStrokeUpdateSource_WetStrokeContinuing 1
CoreWetStrokeUpdateSource_WetStrokeContinuing 2
CoreWetStrokeUpdateSource_WetStrokeContinuing 3
CoreWetStrokeUpdateSource_WetStrokeContinuing 1
CoreWetStrokeUpdateSource_WetStrokeContinuing 2
CoreWetStrokeUpdateSource_WetStrokeContinuing 3
CoreWetStrokeUpdateSource_WetStrokeContinuing 1
CoreWetStrokeUpdateSource_WetStrokeContinuing 2
CoreWetStrokeUpdateSource_WetStrokeContinuing 3
……

CoreWetStrokeUpdateSource_WetStrokeCompleted  1
CoreWetStrokeUpdateSource_WetStrokeContinuing 2
CoreWetStrokeUpdateSource_WetStrokeContinuing 3
CoreWetStrokeUpdateSource_WetStrokeContinuing 2
CoreWetStrokeUpdateSource_WetStrokeContinuing 3
CoreWetStrokeUpdateSource_WetStrokeCompleted2
CoreWetStrokeUpdateSource_WetStrokeContinuing 3
CoreWetStrokeUpdateSource_WetStrokeContinuing 3
CoreWetStrokeUpdateSource_WetStrokeCompleted  3

可以从输出看到在多指触摸的时候，对每个手指都会触发一次完整的 Starting-Continuing-Completed 事件

那么 CoreWetStrokeUpdateSource 和 StrokeContinued 的区别在哪？就是在于触发的先后问题，在笔迹开始书写之前先触发 CoreWetStrokeUpdateSource 事件，然后在书写完成之后触发 StrokeContinued 事件，我同时输出 WetStrokeContinuing 和 StrokeContinued 事件，请看下面

CoreWetStrokeUpdateSource_WetStrokeContinuing 9
StrokeContinued
CoreWetStrokeUpdateSource_WetStrokeContinuing 9
CoreWetStrokeUpdateSource_WetStrokeContinuing 9
CoreWetStrokeUpdateSource_WetStrokeContinuing 9
StrokeContinued
StrokeContinued
CoreWetStrokeUpdateSource_WetStrokeContinuing 9
CoreWetStrokeUpdateSource_WetStrokeContinuing 9
CoreWetStrokeUpdateSource_WetStrokeContinuing 9
CoreWetStrokeUpdateSource_WetStrokeContinuing 9
StrokeContinued
StrokeContinued
CoreWetStrokeUpdateSource_WetStrokeContinuing 9
CoreWetStrokeUpdateSource_WetStrokeContinuing 9
CoreWetStrokeUpdateSource_WetStrokeContinuing 9
StrokeContinued
StrokeContinued
CoreWetStrokeUpdateSource_WetStrokeContinuing 9
CoreWetStrokeUpdateSource_WetStrokeContinuing 9
CoreWetStrokeUpdateSource_WetStrokeContinuing 9
CoreWetStrokeUpdateSource_WetStrokeContinuing 9
CoreWetStrokeUpdateSource_WetStrokeContinuing 9
CoreWetStrokeUpdateSource_WetStrokeContinuing 9
StrokeContinued
StrokeContinued

可以看到 WetStrokeContinuing 的输出时机和频率都会比 StrokeContinued 更高

另外推荐开放的是 StrokeContinued 的事件，因为在使用 UWP 笔迹就是为了做高性能的笔，在 WetStrokeContinuing 的事件里面如果添加了业务代码，那么将会影响笔迹的书写速度

在 UWP 的笔迹书写过程，需要等待 WetStrokeContinuing 事件完成之后才能进行笔迹渲染，而调用 StrokeContinued 事件是在笔迹书写完成之后调用同时不对这个事件做任何的等待

在框架里面建议开放的是 StrokeContinued 触发的事件，减少有逗比开发者在事件里面写了不清真代码降低了笔迹的性能

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