EventTrigger 和 DataTrigger 不能一起工作

Question

我有一个要在ItemsControl 中显示的项目集合。 当一个项目是新的时，它应该淡入，当它的StateType 属性更改为“Finished”时它应该淡出。

我的ItemsControl 的ItemTemplate 是DockPanel

<DockPanel.Style>
    <Style TargetType="{x:Type DockPanel}">
        <Style.Triggers>
            <!-- Fades in as expected but DataTrigger below never fades out -->
            <EventTrigger RoutedEvent="Loaded">
                <BeginStoryboard>
                    <Storyboard>
                        <DoubleAnimation Storyboard.TargetProperty="Opacity" Duration="0:0:1" From="0" To="1"/>
                    </Storyboard>
                </BeginStoryboard>
            </EventTrigger>

    <!-- Using this for fading in everything works fine (first StateType of a new item is Running) -->
    <!--
    <DataTrigger Binding="{Binding StateType}" Value="{x:Static local:AppStateItem+Type.Running}">
        <DataTrigger.EnterActions>
            <BeginStoryboard>
                <Storyboard>
                    <DoubleAnimation Storyboard.TargetProperty="Opacity" Duration="0:0:1" From="0" To="1"/>
                </Storyboard>
            </BeginStoryboard>
        </DataTrigger.EnterActions>
    </DataTrigger>
    -->
            <!-- fade out trigger -->
            <DataTrigger Binding="{Binding StateType}" Value="{x:Static local:AppStateItem+Type.Finished}">
                <DataTrigger.EnterActions>
                    <BeginStoryboard>
                        <Storyboard>
                            <DoubleAnimation Storyboard.TargetProperty="Opacity" Duration="0:0:1" From="1" To="0" BeginTime="0:0:4"/>
                        </Storyboard>
                    </BeginStoryboard>
                </DataTrigger.EnterActions>
            </DataTrigger>
        </Style.Triggers>
    </Style>
</DockPanel.Style>

问题是：它淡入但从不淡出。如果我用注释过的DataTrigger 替换EventTrigger 以使其淡入淡出，它会按预期工作。 EventTrigger 是否会覆盖某些东西，即使它应该只触发一次？

Answer 1

您的示例适用于两个 DataTriggers。

确保实现INotifyPropertyChanged 并为StateType 属性引发PropertyChanged 事件。

您可能还想从第二个Storyboard 中删除BeginTime 设置。

试试这个最小的可重现样本：

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"
        xmlns:local="clr-namespace:WpfApp1"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <DockPanel>
        <DockPanel.Style>
            <Style TargetType="{x:Type DockPanel}">
                <Style.Triggers>
                    <DataTrigger Binding="{Binding StateType}" Value="{x:Static local:AppStateItem.Running}">
                        <DataTrigger.EnterActions>
                            <BeginStoryboard>
                                <Storyboard >
                                    <DoubleAnimation Storyboard.TargetProperty="Opacity" Duration="0:0:1" From="0" To="1"/>
                                </Storyboard>
                            </BeginStoryboard>
                        </DataTrigger.EnterActions>
                    </DataTrigger>
                    <!-- fade out trigger -->
                    <DataTrigger Binding="{Binding StateType}" Value="{x:Static local:AppStateItem.Finished}">
                        <DataTrigger.EnterActions>
                            <BeginStoryboard>
                                <Storyboard>
                                    <DoubleAnimation Storyboard.TargetProperty="Opacity" Duration="0:0:1" From="1" To="0" />
                                </Storyboard>
                            </BeginStoryboard>
                        </DataTrigger.EnterActions>
                    </DataTrigger>
                </Style.Triggers>
            </Style>
        </DockPanel.Style>
        <Button Content="Fade out" Click="Button_Click" DockPanel.Dock="Bottom" />
        <TextBlock FontSize="14" FontWeight="Bold" Text="test" />
    </DockPanel>
</Window>

MainWindow.xaml.cs：

public partial class MainWindow : Window, INotifyPropertyChanged
{
    public MainWindow()
    {
        InitializeComponent();
        DataContext = this;
    }

    private AppStateItem _stateType;
    public AppStateItem StateType
    {
        get { return _stateType; }
        set { _stateType = value; NotifyPropertyChanged(); }
    }

    public event PropertyChangedEventHandler PropertyChanged; 
    private void NotifyPropertyChanged([CallerMemberName] string propertyName = "")
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        StateType = AppStateItem.Finished;
    }
}

public enum AppStateItem
{
    Running,
    Finished
}