[UWP]用Shape做动画(2):使用与扩展PointAnimation

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上一篇几乎都在说DoubleAnimation的应用，这篇说说PointAnimation。

1. 使用PointAnimation

使用PointAnimation可以让Shape变形，但实际上没看到多少人会这么用，毕竟WPF做的软件多数不需要这么花俏。

1.1 在XAML上使用PointAnimation

在这个例子里最头痛的地方是Property-path 语法，如果不能熟记的话最好依赖Blend生成。

1.2 在代码中使用PointAnimation

如果Point数量很多，例如图表，通常会在C#代码中使用PointAnimation：

_storyboard = new Storyboard(); Random random = new Random();for (int i = 0; i < _pathFigure.Segments.Count; i++) { var animation = new PointAnimation { Duration = TimeSpan.FromSeconds(3) }; Storyboard.SetTarget(animation, _pathFigure.Segments[i]); Storyboard.SetTargetProperty(animation, "(LineSegment.Point)"); animation.EnableDependentAnimation = true; animation.EasingFunction = new QuarticEase { EasingMode = EasingMode.EaseOut }; animation.To = new Point((_pathFigure.Segments[i] as LineSegment).Point.X, (i % 2 == 0 ? 1 : -1) * i * 1.2 + 60); _storyboard.Children.Add(animation); } _storyboard.Begin();

因为可以直接SetTarget，所以Property-path语法就可以很简单。

2. 扩展PointAnimation

上面两个例子的动画都还算简单，如果更复杂些，XAML或C#代码都需要写到很复杂。我参考了这个网页想做出类似的动画，但发现需要写很多XAML所以放弃用PointAnimation实现。这个页面的动画核心是这段HTML：

只需一组Point的集合就可以控制所有Point的动画，确实比PointAnimation高效很多。在WPF中可以通过继承Timeline实现一个PointCollectionAnimamtion，具体可以参考这个项目。可惜的是虽然UWP的Timeline类并不封闭，但完全不知道如何继承并派生一个自定义的Animation。

这时候需要稍微变通一下思维。可以将DoubleAnimation理解成这样：Storyboard将TimeSpan传递给DoubleAnimation，DoubleAnimation通过这个TimeSpan（有时还需要结合EasingFunction）计算出目标属性的当前值最后传递给目标属性，如下图所示：

既然这样，也可以接收到这个计算出来的Double，再通过Converter计算出目标的PointCollection值：

假设告诉这个Converter当传入的Double值（命名为Progress）为0的时候，PointCollection是{0,0 1,1 …}，Progress为100时PointCollection是{1,1 2,2 …}，当Progress处于其中任何值时的计算方法则是：

private PointCollection GetCurrentPoints(PointCollection fromPoints, PointCollection toPoints, double percentage) { var result = new PointCollection(); for (var i = 0; i < Math.Min(fromPoints.Count, toPoints.Count); i++) { var x = (1 - percentage / 100d) * fromPoints[i].X + percentage / 100d * toPoints[i].X; var y = (1 - percentage / 100d) * fromPoints[i].Y + percentage / 100d * toPoints[i].Y; result.Add(new Point(x, y)); } return result; }

这样就完成了从TimeSpan到PointCollection的转换过程。然后就是定义在XAML上的使用方式。参考上面PointCollectionAnimation，虽然多了个Converter，但XAML也应该足够简洁：

<local:ProgressToPointCollectionBridge x:Name="ProgressToPointCollectionBridge"> <PointCollection>97.3,0 127.4,60.9 194.6,70.7 145.9,118.1 157.4,185.1 97.3,153.5 37.2,185.1 48.6,118.1 0,70.7 67.2,60.9</PointCollection> <PointCollection>110,58.2 147.3,0 192.1,29 141.7,105.1 118.7,139.8 88.8,185.1 46.1,156.5 0,125 23.5,86.6 71.1,116.7</PointCollection> </local:ProgressToPointCollectionBridge><Storyboard x:Name="Storyboard1" FillBehavior="HoldEnd"> <DoubleAnimation Duration="0:0:2" To="100" FillBehavior="HoldEnd" Storyboard.TargetProperty="(local:ProgressToPointCollectionBridge.Progress)" Storyboard.TargetName="ProgressToPointCollectionBridge" EnableDependentAnimation="True"/> </Storyboard>…<Polygon x:Name="polygon" Points="{Binding Source={StaticResource ProgressToPointCollectionBridge},Path=Points}" Stroke="DarkOliveGreen" StrokeThickness="2" Height="250" Width="250" Stretch="Fill" />

最终我选择了将这个Converter命名为ProgressToPointCollectionBridge。可以看出Polygon 将Points绑定到ProgressToPointCollectionBridge，DoubleAnimation 改变ProgressToPointCollectionBridge.Progress，从而改变Points。XAML的简洁程度还算令人满意，如果需要操作多个点的话相对于PointAnimation的优势就很大。

运行结果如下：

完整的XAML：

<UserControl.Resources> <local:ProgressToPointCollectionBridge x:Name="ProgressToPointCollectionBridge"> <PointCollection>97.3,0 127.4,60.9 194.6,70.7 145.9,118.1 157.4,185.1 97.3,153.5 37.2,185.1 48.6,118.1 0,70.7 67.2,60.9</PointCollection> <PointCollection>110,58.2 147.3,0 192.1,29 141.7,105.1 118.7,139.8 88.8,185.1 46.1,156.5 0,125 23.5,86.6 71.1,116.7</PointCollection> </local:ProgressToPointCollectionBridge> <Storyboard x:Name="Storyboard1" FillBehavior="HoldEnd"> <DoubleAnimation Duration="0:0:2" To="100" FillBehavior="HoldEnd" Storyboard.TargetProperty="(local:ProgressToPointCollectionBridge.Progress)" Storyboard.TargetName="ProgressToPointCollectionBridge" EnableDependentAnimation="True"> <DoubleAnimation.EasingFunction> <ElasticEase EasingMode="EaseInOut" /> </DoubleAnimation.EasingFunction> </DoubleAnimation> <ColorAnimation Duration="0:0:2" To="#FF48F412" Storyboard.TargetProperty="(Shape.Fill).(SolidColorBrush.Color)" Storyboard.TargetName="polygon" d:IsOptimized="True"> <ColorAnimation.EasingFunction> <ElasticEase EasingMode="EaseInOut" /> </ColorAnimation.EasingFunction> </ColorAnimation> </Storyboard> </UserControl.Resources> <Grid x:Name="LayoutRoot" Background="White"> <Polygon x:Name="polygon" Points="{Binding Source={StaticResource ProgressToPointCollectionBridge},Path=Points}" Stroke="DarkOliveGreen" StrokeThickness="2" Height="250" Width="250" Stretch="Fill" Fill="#FFEBF412" /> </Grid>

ProgressToPointCollectionBridge:

[ContentProperty(Name = nameof(Children))] public class ProgressToPointCollectionBridge : DependencyObject { public ProgressToPointCollectionBridge() { Children = new ObservableCollection<PointCollection>(); } /// <summary> /// 获取或设置Points的值 /// </summary> public PointCollection Points { get { return (PointCollection) GetValue(PointsProperty); } set { SetValue(PointsProperty, value); } } /// <summary> /// 获取或设置Progress的值 /// </summary> public double Progress { get { return (double) GetValue(ProgressProperty); } set { SetValue(ProgressProperty, value); } } /// <summary> /// 获取或设置Children的值 /// </summary> public Collection<PointCollection> Children { get { return (Collection<PointCollection>) GetValue(ChildrenProperty); } set { SetValue(ChildrenProperty, value); } } protected virtual void OnProgressChanged(double oldValue, double newValue) { UpdatePoints(); } protected virtual void OnChildrenChanged(Collection<PointCollection> oldValue, Collection<PointCollection> newValue) { var oldCollection = oldValue as INotifyCollectionChanged; if (oldCollection != null) oldCollection.CollectionChanged -= OnChildrenCollectionChanged; var newCollection = newValue as INotifyCollectionChanged; if (newCollection != null) newCollection.CollectionChanged += OnChildrenCollectionChanged; UpdatePoints(); } private void OnChildrenCollectionChanged(object sender, NotifyCollectionChangedEventArgs e) { UpdatePoints(); } private void UpdatePoints() { if (Children == null || Children.Any() == false) { Points = null; } else if (Children.Count == 1) { var fromPoints = new PointCollection(); for (var i = 0; i < Children[0].Count; i++) fromPoints.Add(new Point(0, 0)); var toPoints = Children[0]; Points = GetCurrentPoints(fromPoints, toPoints, Progress); } else { var rangePerSection = 100d / (Children.Count - 1); var fromIndex = Math.Min(Children.Count - 2, Convert.ToInt32(Math.Floor(Progress / rangePerSection))); fromIndex = Math.Max(fromIndex, 0); var toIndex = fromIndex + 1; PointCollection fromPoints; if (fromIndex == toIndex) { fromPoints = new PointCollection(); for (var i = 0; i < Children[0].Count; i++) fromPoints.Add(new Point(0, 0)); } else { fromPoints = Children.ElementAt(fromIndex); } var toPoints = Children.ElementAt(toIndex); var percentage = (Progress / rangePerSection - fromIndex) * 100; Points = GetCurrentPoints(fromPoints, toPoints, percentage); } } private PointCollection GetCurrentPoints(PointCollection fromPoints, PointCollection toPoints, double percentage) { var result = new PointCollection(); for (var i = 0; i < Math.Min(fromPoints.Count, toPoints.Count); i++) { var x = (1 - percentage / 100d) * fromPoints[i].X + percentage / 100d * toPoints[i].X; var y = (1 - percentage / 100d) * fromPoints[i].Y + percentage / 100d * toPoints[i].Y; result.Add(new Point(x, y)); } return result; } #region DependencyProperties #endregion }

3. 结语

如果将DoubleAnimation说成“对目标的Double属性做动画”，那PointAnimation可以说成“对目标的Point.X和Point.Y两个Double属性同时做动画”，ColorAnimation则是“对目标的Color.A、R、G、B四个Int属性同时做动画”。这样理解的话PointAnimation和ColorAnimation只不过是DoubleAnimation的延伸而已，进一步的说，通过DoubleAnimation应该可以延伸出所有类型属性的动画。不过我并不清楚怎么在UWP上自定义动画，只能通过本文的折衷方式扩展。虽然XAML需要写复杂些，但这样也有它的好处：

不需要了解太多Animation相关类的知识，只需要有依赖属性、绑定等基础知识就够了。
不会因为动画API的改变而更改，可以兼容WPF、Silverlight和UWP（大概吧，我没有真的在WPF上测试这些代码）。
代码足够简单，省去了计算TimeSpan及EasingFunction的步骤。稍微修改下还可以做成泛型的AnimationBridge < T >，提供PointCollection以外数据类型的支持。

结合上一篇文章再发散一下，总觉得将来遇到什么UWP没有提供的功能都可以通过变通的方法实现，Binding和DependencyProperty真是UWP开发者最好的朋友。