回答編集履歴

  > 最悪、ControlTemplate自体をコピーして、該当部分を書き換える？と思うのですが、もっとスマートな方法がある気がしてなりません。

 

  `Style`で`BasedOn`するような手軽な方法は、`Template`では残念ながら無いです。

 

  今回の例ですと`ItemContainerStyle`の`Template`で、`MaterialDesignComboBoxItemTemplate`をほぼコピペすることになります。

 

  <Window

  x:Class="Questions302763.MainWindow"

  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

  xmlns:materialDesign="http://materialdesigninxaml.net/winfx/xaml/themes"

  Width="800"

  Height="450">

  <Window.Resources>

  <Style BasedOn="{StaticResource MaterialDesignComboBox}" TargetType="{x:Type ComboBox}">

  <Setter Property="ItemContainerStyle">

  <Setter.Value>

  <Style BasedOn="{StaticResource MaterialDesignComboBoxItemSelectedCollapsedStyle}" TargetType="{x:Type ComboBoxItem}">

  <Setter Property="Template">

  <Setter.Value>

  <ControlTemplate TargetType="{x:Type ComboBoxItem}">

  <Grid x:Name="GridWrapper">

  <Grid.RowDefinitions>

  <RowDefinition Height="Auto" />

  </Grid.RowDefinitions>

 

  <Border

  x:Name="BackBorder"

  Background="{TemplateBinding Background}"

  BorderBrush="{TemplateBinding BorderBrush}"

  BorderThickness="{TemplateBinding BorderThickness}"

  SnapsToDevicePixels="True" />

 

  <Border

  x:Name="SelectedBorder"

  Background="{TemplateBinding Foreground,

  Converter={StaticResource BrushRoundConverter}}"

  Opacity="0"

  RenderTransformOrigin="0.5,0.5" />

  <materialDesign:Ripple

  Padding="{TemplateBinding Padding}"

  HorizontalAlignment="Stretch"

  VerticalAlignment="Stretch"

  HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}"

  VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}"

  Content="{TemplateBinding Content}"

  ContentTemplate="{TemplateBinding ContentTemplate}"

  ContentTemplateSelector="{TemplateBinding ContentTemplateSelector}"

  Feedback="{TemplateBinding Foreground,

  Converter={StaticResource BrushRoundConverter}}"

  Focusable="False"

  RecognizesAccessKey="False"

  SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" />

  <VisualStateManager.VisualStateGroups>

  <VisualStateGroup Name="CommonStates">

  <VisualStateGroup.Transitions>

  <VisualTransition GeneratedDuration="0:0:0.1" To="Normal">

  <VisualTransition.GeneratedEasingFunction>

  <CircleEase EasingMode="EaseOut" />

  </VisualTransition.GeneratedEasingFunction>

  </VisualTransition>

  </VisualStateGroup.Transitions>

  <VisualState Name="Normal" />

  <VisualState Name="MouseOver">

  <Storyboard>

  <DoubleAnimation

  Storyboard.TargetName="MouseOverBorder"

  Storyboard.TargetProperty="Opacity"

  To="0.1"

  Duration="0" />

  </Storyboard>

  </VisualState>

  </VisualStateGroup>

  <VisualStateGroup Name="SelectionStates">

  <VisualStateGroup.Transitions>

  <VisualTransition GeneratedDuration="0:0:0.1" />

  </VisualStateGroup.Transitions>

  <VisualState Name="Selected">

  <Storyboard>

  <DoubleAnimation

  Storyboard.TargetName="SelectedBorder"

  Storyboard.TargetProperty="Opacity"

  To="0.18"

  Duration="0" />

  </Storyboard>

  </VisualState>

  <VisualState Name="Unselected" />

  </VisualStateGroup>

  <VisualStateGroup Name="FocusStates">

  <VisualStateGroup.Transitions>

  <VisualTransition GeneratedDuration="0:0:0.1" To="Unfocused" />

  </VisualStateGroup.Transitions>

  <VisualState Name="Focused">

  <Storyboard>

  <DoubleAnimation

  Storyboard.TargetName="MouseOverBorder"

  Storyboard.TargetProperty="Opacity"

  To="0.1"

  Duration="0" />

  </Storyboard>

  </VisualState>

  <VisualState Name="Unfocused" />

  </VisualStateGroup>

  </VisualStateManager.VisualStateGroups>

  </Grid>

  <ControlTemplate.Triggers>

  <Trigger Property="IsEnabled" Value="False">

  <Setter TargetName="GridWrapper" Property="Opacity" Value="0.56" />

  </Trigger>

  <MultiTrigger>

  <MultiTrigger.Conditions>

  <Condition Property="Tag" Value="{StaticResource AllowCollapse}" />

  <Condition Property="IsSelected" Value="True" />

  </MultiTrigger.Conditions>

  <Setter Property="Height" Value="0" />

  </MultiTrigger>

  </ControlTemplate.Triggers>

  </ControlTemplate>

  </Setter.Value>

  </Setter>

  </Style>

  </Setter.Value>

  </Setter>

  </Style>

  </Window.Resources>

  <Grid>

  <StackPanel>

  <GroupBox Header="ノーマル">

  <ComboBox Style="{StaticResource MaterialDesignComboBox}">

  <ComboBoxItem>aaa</ComboBoxItem>

  <ComboBoxItem>bbb</ComboBoxItem>

  <ComboBoxItem>ccc</ComboBoxItem>

  </ComboBox>

  </GroupBox>

 

  <GroupBox Header="キビキビ">

  <ComboBox>

  <ComboBoxItem>aaa</ComboBoxItem>

  <ComboBoxItem>bbb</ComboBoxItem>

  <ComboBoxItem>ccc</ComboBoxItem>

  </ComboBox>

  </GroupBox>

  </StackPanel>

  </Grid>

  </Window>

  ```

 

  ---

 

  s.promptさんとまったく同じことを思っている方はいるようですが、クローズしています（前向きに検討中なのか・やる気はないのかは、自動翻訳では読み取れなかったです^^;

  [Adding support for customization of visualtransition duration of combobox item to normal state by koutinho · Pull Request #1290 · MaterialDesignInXAML/MaterialDesignInXamlToolkit](https://github.com/MaterialDesignInXAML/MaterialDesignInXamlToolkit/pull/1290)