如何将SelectionChanged事件绑定到XAML中其他元素的可见性上

Question

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给出SelectionChanged之后的ComboBox应该成为可见的TextBlock。我使用ViemModel构建此功能。

查看：

<ComboBox SelectionChanged="{mvvmHelper:EventBinding OnSelectionChanged}" />
<TextBlock Visibility="{Binding LanguageChanged, Converter={StaticResource BooleanVisibilityConverter}}"/>

ViewModel：

bool LanguageChanged = false;

void OnSelectionChanged() => LanguageChanged = true;

我正在寻找仅在XAML中完成的优雅解决方案

到目前为止我尝试过的事情：

<Style TargetType="{x:Type TextBlock}">
    <Setter Property="Visibility" Value="Collapsed" />
    <Style.Triggers>
        <DataTrigger Binding="{Binding IsDropDownOpen, ElementName=Box, Mode=OneWay, UpdateSourceTrigger=PropertyChanged}" Value="True">
            <Setter Property="Visibility" Value="Visible" />
        </DataTrigger>
    </Style.Triggers>
</Style>

我想我必须使用情节提要

<ComboBox.Style>
    <Style TargetType="{x:Type ComboBox}">
        <Style.Triggers>
            <EventTrigger RoutedEvent="SelectionChanged">
                <BeginStoryboard>
                    <Storyboard>
                        ???
                    </Storyboard>
                </BeginStoryboard>
            </EventTrigger>
        </Style.Triggers>
    </Style>
</ComboBox.Style>

另一个选项是System.Windows.Interactivity，但这在WpfCore 3.1中不可用

Answer 1

您在这里有几个不错的选择。

设置触发器属性的动画

为了给LanguageChanged之类的属性设置动画，该属性必须为DependencyProperty。因此，第一个示例将LanguageChanged实现为DependencyProperty的MainWindow：

MainWindow.xaml.cs

partial class MainWindow : Window
{
  public static readonly DependencyProperty LanguageChangedProperty = DependencyProperty.Register(
    "IsChanged",
    typeof(bool),
    typeof(MainWindow),
    new PropertyMetadata(default(bool)));

  public bool LanguageChanged
  {
    get => (bool) GetValue(MainWindow.LanguageChangedProperty);
    set => SetValue(MainWindow.LanguageChangedProperty, value);
  }
}

MainWindow.xaml

<Window x:Name="Window">
  <StackPanel>

    <TextBlock Text="Invisible"
               Visibility="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType=MainWindow}, Path=LanguageChanged, Converter={StaticResource BooleanToVisibilityConverter}}" />

    <ComboBox>
      <ComboBox.Triggers>
        <EventTrigger RoutedEvent="ComboBox.SelectionChanged">
          <BeginStoryboard>
            <Storyboard>
              <BooleanAnimationUsingKeyFrames Storyboard.TargetName="Window"
                                              Storyboard.TargetProperty="LanguageChanged">
                <DiscreteBooleanKeyFrame KeyTime="0" Value="True" />
              </BooleanAnimationUsingKeyFrames>
            </Storyboard>
          </BeginStoryboard>
        </EventTrigger>
      </ComboBox.Triggers>
    </ComboBox>
  </StackPanel>
</Window>

---

直接对目标控件进行动画处理

如果您希望切换可见性的控件与触发控件的范围相同，则可以直接为Visibility设置动画：

MainWindow.xaml

<Window x:Name="Window">
  <StackPanel>

    <TextBlock x:Name="InvisibleTextBlock"
               Text="Invisible"
               Visibility="Hidden" />

    <ComboBox>
      <ComboBox.Triggers>
        <EventTrigger RoutedEvent="ComboBox.SelectionChanged">
          <BeginStoryboard>
            <Storyboard>
              <ObjectAnimationUsingKeyFrames Storyboard.TargetName="InvisibleTextBlock"
                                             Storyboard.TargetProperty="Visibility">
                <DiscreteObjectKeyFrame KeyTime="0" Value="{x:Static Visibility.Visible}" />
              </BooleanAnimationUsingKeyFrames>
            </Storyboard>
          </BeginStoryboard>
        </EventTrigger>
      </ComboBox.Triggers>
    </ComboBox>
  </StackPanel>
</Window>

---

实现IValueConverter

如果要向触发器添加更多条件（如选择了哪个值），则应将TextBlock.Visibility绑定到ComboBox.SelectedItem，并使用IValueConverter决定是否基于返回Visibility.Visible或Visibilty.Hidden当前选择的项目：

MainWindow.xaml

<Window x:Name="Window">
  <Window.Resources>

    <!-- TODO::Implement IValueConverter -->
    <SelectedItemToVisibilityConverter x:Key="SelectedItemToVisibilityConverter" />
  <StackPanel>

    <TextBlock Text="Invisible"
               Visibility="{Binding ElementName=LanguageSelector, Path=SelectedItem, Converter={StaticResource SelectedItemToVisibilityConverter}}" />

    <ComboBox x:Name="LanguageSelector" />
  </StackPanel>
</Window>