DataTrigger.ExistActions 未触发绑定值“null”

Question

我有以下数据触发器，但退出操作没有触发。输入动作工作发现。我还尝试将 Binding 转换为布尔值，以查看它是否与 null 有关，但这也无济于事。我有什么问题，为什么我的退出操作没有在这里触发？

<DataTrigger  Binding="{Binding }" Value="{x:Null}">
    <DataTrigger.EnterActions>
        <BeginStoryboard>
            <Storyboard>
                <DoubleAnimation Storyboard.TargetProperty="Opacity"  To=".5" From="0" Duration="0:0:1"></DoubleAnimation>
            </Storyboard>
        </BeginStoryboard>
    </DataTrigger.EnterActions>
    <DataTrigger.ExitActions>
        <BeginStoryboard>
            <Storyboard>
                <DoubleAnimation Storyboard.TargetProperty="Opacity"  To="0" From=".5" Duration="0:0:1"></DoubleAnimation>
            </Storyboard>
        </BeginStoryboard>
    </DataTrigger.ExitActions>
</DataTrigger>

编辑：这里肯定发生了一些奇怪的事情，因为我也尝试过将故事板排除在等式之外并只使用 Setters——现在什么都没有发生......

所以，代替这个，我将发布整个 TextBlock，也许有人可以指出我错过了什么

<Grid DataContext="{Binding ElementName=ConfigTree, Path=SelectedItem.Details}">


                    <TextBlock HorizontalAlignment="Center" TextWrapping="Wrap" TextAlignment="Center" Padding="10" VerticalAlignment="Center" FontWeight="Bold" FontSize="14" Opacity="0">
                        Select a configuration on the right to modify its selected columns
                        <TextBlock.Style>
                            <Style TargetType="TextBlock"  BasedOn="{StaticResource {x:Type TextBlock}}">
                                <Style.Triggers>
                                    <DataTrigger  Binding="{Binding }" Value="{x:Null}">
                                        <DataTrigger.EnterActions>
                                            <BeginStoryboard>
                                                <Storyboard  Duration="0:0:1">
                                                    <DoubleAnimation Storyboard.TargetProperty="Opacity"  To=".5" From="0" Duration="0:0:1"></DoubleAnimation>
                                                </Storyboard>
                                            </BeginStoryboard>
                                        </DataTrigger.EnterActions>
                                        <DataTrigger.ExitActions>
                                            <BeginStoryboard>
                                                <Storyboard>
                                                    <DoubleAnimation Storyboard.TargetProperty="Opacity"  To="0" From=".5" Duration="0:0:1"></DoubleAnimation>
                                                </Storyboard>
                                            </BeginStoryboard>
                                        </DataTrigger.ExitActions>
                                    </DataTrigger>
                                </Style.Triggers>
                            </Style>
                        </TextBlock.Style>
                    </TextBlock>

ConfigTree 是一个树视图，SelectedItem.Details 是一个实现 observablecollection 和 INotifyPropertyChanged 的​​类。我已经检查了调试器，这个绑定正在正确更新，并且在我的实例值和空值之间来回切换。

Answer 1

对我来说很好用！

         <CheckBox x:Name="MyCheckBox"
                   IsThreeState="True"
                   Content="I am Tristate! Check Me"/>

         <TextBox x:Name="MyTextBlock"
                  Background="Cyan"
                  Text="1234567890">
            <TextBox.Style>
                <Style TargetType="{x:Type TextBox}">
                    <Style.Triggers>
                        <DataTrigger 
                            Binding="{Binding ElementName=MyCheckBox,
                                              Path=IsChecked}"
                            Value="{x:Null}">
                            <DataTrigger.EnterActions>
                                <BeginStoryboard>
                                    <Storyboard>
                                        <DoubleAnimation
                                          Storyboard.TargetProperty="Opacity"
                                          To=".5" From="0"
                                          Duration="0:0:1">
                                        </DoubleAnimation>
                                    </Storyboard>
                                </BeginStoryboard>
                            </DataTrigger.EnterActions>
                            <DataTrigger.ExitActions>
                                <BeginStoryboard>
                                    <Storyboard>
                                        <DoubleAnimation
                                          Storyboard.TargetProperty="Opacity"
                                          To="0" From="0.5"
                                          Duration="0:0:1">
                                        </DoubleAnimation>
                                    </Storyboard>
                                </BeginStoryboard>
                            </DataTrigger.ExitActions>
                        </DataTrigger>
                    </Style.Triggers>
                </Style>
            </TextBox.Style>
        </TextBox>