WPF 开启Pointer消息存在的坑

本文记录在 WPF 开启 Pointer 消息的坑

屏幕键盘

启用了Pointer之后，调用Textbox.Focus()，起不来屏幕键盘，必须点在它之上才行，触摸在它之上才行

使用屏幕绝对坐标而不是窗口坐标

默认 Pointer 消息是使用屏幕绝对坐标而不是窗口坐标

可能存在获取 Stylus 事件时触摸点不准，此时可以通过获取 Touch 代替，详细请看 WPF will have a touch offset after trun on the WM_Pointer message · Issue #3360 · dotnet/wpf 此问题应该在 Fix raw stylus data to support per-monitor DPI by rladuca · Pull Request #2891 · dotnet/wpf 修复

开启 Pointer 消息之后无法隐藏触摸反馈点

开启 Pointer 消息之后，调用 Stylus.IsPressAndHoldEnabled="False" 无效

在没有开启 Pointer 消息，将会在 System.Windows.Interop.HwndSource 的 Initialize 方法通过判断是否开启 Pointer 消息执行 HwndStylusInputProvider 逻辑

            if (StylusLogic.IsStylusAndTouchSupportEnabled)
            {
                // Choose between Wisp and Pointer stacks
                if (StylusLogic.IsPointerStackEnabled)
                {
                	// 开启 Pointer 的逻辑
                    _stylus = new SecurityCriticalDataClass<IStylusInputProvider>(new HwndPointerInputProvider(this));
                }
                else
                {
                    _stylus = new SecurityCriticalDataClass<IStylusInputProvider>(new HwndStylusInputProvider(this));
                }
            }

在 HwndStylusInputProvider 将会读取 IsPressAndHoldEnabledProperty 属性，然后使用 WM_TABLET_QUERYSYSTEMGESTURESTATUS 返回 1 的方式告诉系统不显示触摸反馈点。也就是 WPF 隐藏触摸反馈点是通过 How do I disable the press-and-hold gesture for my window 的方法

如果不设置 Stylus.IsPressAndHoldEnabled="False" 也可以自己手动监听消息，在消息 WM_TABLET_QUERYSYSTEMGESTURESTATUS 里面返回 1 就可以告诉系统不显示触摸反馈点

       private IntPtr Hook(IntPtr hwnd, int msg, IntPtr wparam, IntPtr lparam, ref bool handled)
        {
            const int WM_TABLET_DEFBASE =0x02C0;
            const int WM_TABLET_QUERYSYSTEMGESTURESTATUS = WM_TABLET_DEFBASE + 12;
            const int WM_TABLET_FLICK = WM_TABLET_DEFBASE + 11;

            if (msg == WM_TABLET_QUERYSYSTEMGESTURESTATUS)
            {
                uint flags = 0;

                flags |= TABLET_PRESSANDHOLD_DISABLED;
                flags |= TABLET_TAPFEEDBACK_DISABLED;
                flags |= TABLET_TOUCHUI_FORCEON;
                flags |= TABLET_TOUCHUI_FORCEOFF;
                flags |= TABLET_FLICKS_DISABLED;

                handled = true;
                return new IntPtr(flags);
            }
            else if (msg == WM_TABLET_FLICK)
            {
                handled = true;
                return new IntPtr(1);
            }

            return IntPtr.Zero;
        }

        private const uint TABLET_PRESSANDHOLD_DISABLED = 0x00000001;
        private const uint TABLET_TAPFEEDBACK_DISABLED = 0x00000008;
        private const uint TABLET_TOUCHUI_FORCEON = 0x00000100;
        private const uint TABLET_TOUCHUI_FORCEOFF = 0x00000200;
        private const uint TABLET_FLICKS_DISABLED = 0x00010000;