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开发环境

VS2022

.NET 8.0

MVVM Toolkit 8.2.2

需求

开发中需要实现按照成绩动态指名，以展示当前的竞赛成绩的一个实时情况及变化。

即如下效果：

需求分析

按照接收到的信息，就是要将获取到的集合排序，并且要将排序前后的变化，要能在UI上动态的表示出来，以直观的显示排名的变化效果。

UI上的排名上升与下降的实现，本质就是当前显示控件位置的变化，最方便的方式肯定是在Canvas上设置它的Top位置了，然后再有一个从原位置到新位置的过度动画，那么就好了。

按上述思路，首先想到的就是自定义控件，完全自定义控件有点麻烦，最后决定使用常用的集合控件 ItemsControl（其子控件也行，但仅用ListView尝试过）来进行实现。

代码实现

VM及Model：

    internal partial class MainWindowViewModel : ObservableRecipient{[ObservableProperty]ObservableCollection<Person> persons =[new Person() { Id = 1, Name = "张三", Age = 18, Gender = "男", Address = "北京", Grade = "一年级" ,Y=50,OldY=50,Score=40},new Person() { Id = 2, Name = "李四", Age = 19, Gender = "女", Address = "上海", Grade ="二年级",Y=100,OldY=100,Score=60},new Person() { Id = 3, Name = "王五", Age = 20, Gender = "男", Address = "广州", Grade = "三年级" ,Y=150,OldY=150,Score=90},];Timer timer;public MainWindowViewModel(){timer = new Timer(OnTimer, null, 0,1000);}private void OnTimer(object? state){Dispatcher.CurrentDispatcher.Invoke(() =>{Random random = new();var index = random.Next(0, 3);Persons[index].Score = random.Next(0, 100);var sorts = Persons.OrderBy(p => p.Score);int i = 0;foreach (var item in sorts){item.Id = ++i;item.Y = i * 50;}});}}public partial class Person : ObservableObject{[ObservableProperty]private int id;[ObservableProperty]private string name;[ObservableProperty]private int age;[ObservableProperty]private string gender;[ObservableProperty]private string address;[ObservableProperty]private string grade;private int y;public int Y{get => y;set{if (y != value){OldY = y; //记录旧值SetProperty(ref y, value);}}}[ObservableProperty]private int oldY;[ObservableProperty]private int score;}

Xaml中绑定如下，注意下述代码中的ZContentPresenter为自定义控件：

 <ItemsControlx:Name="myItemsControl"Margin="10"ItemsSource="{Binding Persons}"><ItemsControl.ItemsPanel><ItemsPanelTemplate><Canvas /></ItemsPanelTemplate></ItemsControl.ItemsPanel><ItemsControl.ItemTemplate><DataTemplate><control:ZContentPresenterx:Name="presenter"Content="{Binding}"Top="{Binding Y}"><ContentPresenter.ContentTemplate><DataTemplate><StackPanel Orientation="Horizontal"><TextBox Text="{Binding Id}" /><TextBox Text="{Binding Name}" /><TextBox Text="{Binding Age}" /><TextBox Text="{Binding Y}" /></StackPanel></DataTemplate></ContentPresenter.ContentTemplate></control:ZContentPresenter></DataTemplate></ItemsControl.ItemTemplate></ItemsControl>

对于 UI中的ZContentPresenter为自定义控件，其代码如下：

    public class ZContentPresenter : ContentPresenter{public ZContentPresenter(){}public int Top{get { return (int)GetValue(TopProperty); }set { SetValue(TopProperty, value); }}public static readonly DependencyProperty TopProperty =DependencyProperty.Register("Top", typeof(int), typeof(ZContentPresenter), new PropertyMetadata(0, TopChanged));private static void TopChanged(DependencyObject d, DependencyPropertyChangedEventArgs e){if (d is ZContentPresenter control){var oldValue = (int)e.OldValue;var newValue = (int)e.NewValue;var parent=(ContentPresenter)control.VisualParent;StartAnimation((double)(oldValue), (double)(newValue), parent);}}private static void StartAnimation(double from, double to, FrameworkElement element){Storyboard storyboard = new();DoubleAnimation animation = new(){From = from,To = to,Duration = TimeSpan.FromSeconds(0.5),AutoReverse = false,RepeatBehavior = new RepeatBehavior(1)};Storyboard.SetTarget(animation, element);Storyboard.SetTargetProperty(animation, new PropertyPath(Canvas.TopProperty));//Storyboard.SetTargetProperty(animation, new PropertyPath("(Canvas.Top)"));storyboard.Children.Add(animation);storyboard.Begin();
/*            storyboard.Completed += (sender, e) =>{storyboard.Stop();};*/}}

那为什么不直接在ItemContainerStyle中直接使用样式与Trigger中设置动画来实现呢？

这涉及到Trigger不能侦听Y值的实时变化，另外还有一个问题就是在Animation中不能绑定From与To值，若From或To采用绑定，会导致出现报错：无法冻结此 Storyboard 时间线树供跨线程使用。

注意事项

1. 自定义控件中的

 Storyboard.SetTargetProperty(animation, new PropertyPath("(Canvas.Top)"));

这种写法与

Storyboard.SetTargetProperty(animation, new PropertyPath(Canvas.TopProperty));

是等价的，并且不能将括号去掉。

2. 另外就是一定要绑定Top属性为你指定的离Canvas顶部的距离，本例中以Y值进行绑定

3. 虽然已经将ItemsControl中的DataTemplate的ContentPresneter改用了ZContentPresneter(即使将ContentPresenter.ContentTemplate也改为了ZContentPresneter.ContentTemplate,也没有效果)，但若要改写ItemsControl的ItemContainerStyle，它的TargetType仍还是只能为ContentPresenter，它的默认容器就是ContentPresenter，暂未发现如何将默认的容器改为ZContentPresneter。也就是说目前还只能如下设置：

            <ItemsControl.ItemContainerStyle><Style TargetType="ContentPresenter"><Setter Property="Canvas.Left" Value="0" /><Setter Property="Canvas.Top" Value="{Binding OldY}" /><Style.Triggers><DataTrigger Binding="{Binding Y, UpdateSourceTrigger=PropertyChanged}" Value="50"><DataTrigger.EnterActions><BeginStoryboard><Storyboard><DoubleAnimationAutoReverse="false"RepeatBehavior="1"Storyboard.TargetProperty="(Canvas.Top)"From="5"To="20"Duration="0:0:1" /></Storyboard></BeginStoryboard></DataTrigger.EnterActions></DataTrigger></Style.Triggers></Style></ItemsControl.ItemContainerStyle>