WPF：绑定更改时如何触发 EventTrigger（或动画）？

Question

我们有一个简单的动画，当检查并取消选中ToggleButton时运行（展开ListView的高度，然后折叠ListView的高度）。当以下 XAML 中 x:Name="DetailsGrid" 网格中的 DataContext 绑定发生变化时，如何为 <Storyboard x:Key="CommentsCollapse"> 触发 EventTrigger（或动画）？

换句话说，每当“DetailsGrid”的 Binding 发生变化时，我们都希望触发“CommentsCollapse” StoryBoard 以确保 ListView 返回到其折叠状态。

<Page
   xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
   xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
   Width="800"
   Height="400">
   <Page.Resources>
      <Storyboard x:Key="CommentsExpand">
         <DoubleAnimationUsingKeyFrames
            BeginTime="00:00:00"
            Storyboard.TargetName="CommentsListView"
            Storyboard.TargetProperty="(FrameworkElement.Height)">
            <SplineDoubleKeyFrame KeyTime="00:00:00.200" Value="300"/>
         </DoubleAnimationUsingKeyFrames>
      </Storyboard>
      <Storyboard x:Key="CommentsCollapse">
         <DoubleAnimationUsingKeyFrames
            BeginTime="00:00:00"
            Storyboard.TargetName="CommentsListView"
            Storyboard.TargetProperty="(FrameworkElement.Height)">
            <SplineDoubleKeyFrame KeyTime="00:00:00.200" Value="75"/>
         </DoubleAnimationUsingKeyFrames>
      </Storyboard>
   </Page.Resources>
   <Page.Triggers>
      <EventTrigger RoutedEvent="ToggleButton.Checked" SourceName="CommentsToggleButton">
         <BeginStoryboard Storyboard="{StaticResource CommentsExpand}"/>
      </EventTrigger>
      <EventTrigger RoutedEvent="ToggleButton.Unchecked" SourceName="CommentsToggleButton">
         <BeginStoryboard Storyboard="{StaticResource CommentsCollapse}"/>
      </EventTrigger>
   </Page.Triggers>
   <Grid DataContext="{Binding Path=CurrentTask.Workflow.Invoice}" x:Name="DetailsGrid">
      <StackPanel Orientation="Horizontal">
         <Canvas Width="428">
            <GroupBox Width="422" Margin="5,0,0,0">
               <GroupBox.Header>
                  <StackPanel Orientation="Horizontal">
                     <ToggleButton
                        x:Name="CommentsToggleButton"
                        Width="20"
                        Height="10"
                        Margin="5,0,0,0">
                        <ToggleButton.Content>
                           <Rectangle
                              Width="5"
                              Height="5"
                              Fill="Red"/>
                        </ToggleButton.Content>
                     </ToggleButton>
                     <TextBlock Foreground="Blue" Text="Comments"/>
                  </StackPanel>
               </GroupBox.Header>
               <ListView
                  x:Name="CommentsListView"
                  Height="75"
                  ItemsSource="{Binding Path=Comments}">
                  <ListView.View>
                     <GridView>
                        <GridViewColumn DisplayMemberBinding="{Binding Path=Date}" Header="Date"/>
                        <GridViewColumn DisplayMemberBinding="{Binding Path=Name}" Header="User"/>
                        <GridViewColumn DisplayMemberBinding="{Binding Path=Description}" Header="Comment"/>
                     </GridView>
                  </ListView.View>
               </ListView>
            </GroupBox>
         </Canvas>
      </StackPanel>
   </Grid>
</Page>

Answer 1

我认为你不能通过纯 Xaml 来做到这一点，你必须在代码中做到这一点（或者更好的是，编写一个通用的表达式行为，以便你可以用Xml)。查看 Dependency Property 的 PropertyMetadata，了解如何挂钩其 Property Changed 事件。

Answer 2

我也发现这在 XAML 中是不可能的。您需要 DataContextChanged 事件，它不是 RoutedEvent，因此不能在 EventTrigger 中使用。

这似乎可行：

<Window x:Class="DatacontextChangedSpike.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="300" Width="300">
    <Window.Resources>
        <Storyboard x:Key="ListViewExpands" AutoReverse="True" RepeatBehavior="2x">
            <DoubleAnimation Storyboard.TargetName="PulsingListView" Storyboard.TargetProperty="Height"
                            From="10" To="60"/>
        </Storyboard>
    </Window.Resources>
    <StackPanel>
        <ListView Name="PulsingListView" BorderThickness="2" BorderBrush="Black"
                  DataContextChanged="PulsingListView_DataContextChanged">
            <TextBlock>Listview</TextBlock>
        </ListView>
        <Button Click="Button_Click" >Change DataContext</Button>
    </StackPanel>
</Window>

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Media.Animation;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace DatacontextChangedSpike
{
    public partial class Window1 : Window
    {
        public Window1()
        {
            DataContext = new List<string>();
            InitializeComponent();
        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            DataContext = new List<int>();
        }

        private void PulsingListView_DataContextChanged(object sender, DependencyPropertyChangedEventArgs e)
        {
            var sb = (Storyboard)FindResource("ListViewExpands");
            sb.Begin();
        }
    }
}

Answer 3

如果您可以在更改 DataContext 时将 ViewModel 属性设置为 true 或 false，则可以从 DataTrigger（EnterAction 和 ExitAction）触发 StoryBoard。因此 DataTrigger 将基于您的新 Bool 属性。