使用Storyboard动画后无法拖动GridSplitter

[VBProFan]

程序运行起来后界面如图，蓝块和红块之间有个GridSplitter，用鼠标左右拖动可以调整左右两块的大小。点击蓝块左侧的按钮后鼠标移到GridSplitter的位置仍然会变为左右箭头的指针，但是无法再调整大小，为什么？

MainWindow.xaml:

<Window x:Class="WpfApp1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="20"/>
            <ColumnDefinition x:Name="MenuList" Width="*"/>
            <ColumnDefinition Width="auto"/>
            <ColumnDefinition Width="*"/>
        </Grid.ColumnDefinitions>

        <Button Name="cmd"
                Grid.Column="0"
                Click="Button_Click" />

        <TextBlock Grid.Column="1"
                   Background="Blue" />

        <GridSplitter 
                Grid.Column="2" 
                Width="3" 
                HorizontalAlignment="Stretch" 
                DragCompleted="GridSplitter_DragCompleted" />

        <TextBlock Grid.Column="3"
                   Background="Red" />
    </Grid>
</Window>

MainWindow.xaml.cs:

using System;
using System.Windows;
using System.Windows.Media.Animation;

namespace WpfApp1
{
    public partial class MainWindow : Window
    {
        int PanelWidth = 200;
        public MainWindow()
        {
            InitializeComponent();
            MenuList.Width = new GridLength(PanelWidth);
        }
        private void slideSubMenu(DependencyObject animateObject, GridLength from, GridLength to)
        {
            Storyboard storyboard = new Storyboard();
            GridLengthAnimation widthAnimation = new GridLengthAnimation()
            {
                From = from,
                To = to,
                Duration = new Duration(TimeSpan.FromSeconds(0.3))
            };
            Storyboard.SetTarget(widthAnimation, animateObject);
            Storyboard.SetTargetProperty(widthAnimation, new PropertyPath("(Width)"));
            storyboard.Children.Add(widthAnimation);
            storyboard.Begin();
        }
        private void Button_Click(object sender, RoutedEventArgs e)
        {
            bool bSubMenuVisible = (MenuList.Width == new GridLength(PanelWidth));
            double toGridLength = bSubMenuVisible ? 0 : PanelWidth;

            slideSubMenu(MenuList, MenuList.Width, new GridLength(toGridLength));
            //如果屏蔽上面那句，启用下面那句，则 GridSplitter 能正常拖动
            //MenuList.Width = new GridLength(toGridLength);
        }

        private void GridSplitter_DragCompleted(object sender, System.Windows.Controls.Primitives.DragCompletedEventArgs e)
        {
            PanelWidth = (int)MenuList.ActualWidth;
        }
    }
}

GridLengthAnimation.cs:

using System;
using System.Windows;
using System.Windows.Media.Animation;

namespace WpfApp1
{
    public class GridLengthAnimation : AnimationTimeline
    {
        public override Type TargetPropertyType => typeof(GridLength);

        protected override Freezable CreateInstanceCore()
        {
            return new GridLengthAnimation();
        }

        public static readonly DependencyProperty FromProperty = DependencyProperty.Register("From", typeof(GridLength), typeof(GridLengthAnimation));

        public GridLength From
        {
            get
            {
                return (GridLength)GetValue(FromProperty);
            }
            set
            {
                SetValue(FromProperty, value);
            }
        }

        public static readonly DependencyProperty ToProperty = DependencyProperty.Register("To", typeof(GridLength), typeof(GridLengthAnimation));

        public GridLength To
        {
            get
            {
                return (GridLength)GetValue(ToProperty);
            }
            set
            {
                SetValue(ToProperty, value);
            }
        }

        public const string EasingFunctionPropertyName = "EasingFunction";

        public IEasingFunction EasingFunction
        {
            get
            {
                return (IEasingFunction)GetValue(EasingFunctionProperty);
            }
            set
            {
                SetValue(EasingFunctionProperty, value);
            }
        }

        public static readonly DependencyProperty EasingFunctionProperty = DependencyProperty.Register(
            EasingFunctionPropertyName,
            typeof(IEasingFunction),
            typeof(GridLengthAnimation),
            new UIPropertyMetadata(null));

        public override object GetCurrentValue(object defaultOriginValue, object defaultDestinationValue, AnimationClock animationClock)
        {
            double fromVal = ((GridLength)GetValue(FromProperty)).Value;
            double toVal = ((GridLength)GetValue(ToProperty)).Value;
            double progress = animationClock.CurrentProgress.Value;

            IEasingFunction easingFunction = EasingFunction;
            if (easingFunction != null)
            {
                progress = easingFunction.Ease(progress);
            }

            if (fromVal > toVal)
            {
                progress = 1 - progress;
            }

            double v = progress * Math.Abs(fromVal - toVal) + Math.Min(fromVal, toVal);
            return new GridLength(v, GridUnitType.Pixel);
        }
    }
}

[VBProFan]

搞定！ 增加： widthAnimation.FillBehavior = FillBehavior.Stop; 恢复： MenuList.Width = new GridLength(toGridLength); 参看： https://msdn.microsoft.com/zh-cn/library/aa970493.aspx?cs-save-lang=1&cs-lang=csharp#code-snippet-4

[Milo米啊米啊米]

引用 2 楼 VBProFan 的回复:

[quote=引用 1 楼 Libby1984 的回复:] 你如果为某个控件的某个属性应用了动画，动画执行后如果想在代买修改那个属性才值，必须要接触动画的绑定。如果你为GridSplitter的Width属性绑定了动画，可以用这样：GridSplitter.BeginAnimation(FrameworkElement.WidthProperty, null); 然后就可以修改宽度的值。

谢谢！这思路听起来很有道理，我试着在 storyboard.Begin(); 后加了一句 MenuList.BeginAnimation(WidthProperty, null); 还是不行。不过已经有研究的方向了，再次感谢！[/quote] 你试试用MenuList.BeginAnimation启动动画，结束后用MenuList.BeginAnimation设置为空

[Milo米啊米啊米]

你如果为某个控件的某个属性应用了动画，动画执行后如果想在代买修改那个属性才值，必须要接触动画的绑定。如果你为GridSplitter的Width属性绑定了动画，可以用这样：GridSplitter.BeginAnimation(FrameworkElement.WidthProperty, null); 然后就可以修改宽度的值。

[VBProFan]

引用 1 楼 Libby1984 的回复:

你如果为某个控件的某个属性应用了动画，动画执行后如果想在代买修改那个属性才值，必须要接触动画的绑定。如果你为GridSplitter的Width属性绑定了动画，可以用这样：GridSplitter.BeginAnimation(FrameworkElement.WidthProperty, null); 然后就可以修改宽度的值。

谢谢！这思路听起来很有道理，我试着在 storyboard.Begin(); 后加了一句 MenuList.BeginAnimation(WidthProperty, null); 还是不行。不过已经有研究的方向了，再次感谢！

[VBProFan]

如果是加 Storyboard.SetTarget(null, animateObject); 则发生运行时错误：值不能为null