wpf如何修改combobox的三角形颜色为红色

您可以使用 WPF 的 ControlTemplate 和 VisualStateManager 来修改 ComboBox 的三角形颜色为红色。首先，您需要将 ComboBox 控件的 ControlTemplate 属性设置为一个自定义的模板，该模板包含了一个名为 "Arrow" 的 Path 控件。在 "Arrow" 控件的 Fill 属性中设置为红色即可。同时，您可以使用 VisualStateManager 来定义不同状态下的样式，例如鼠标悬停和选中状态等。以下是一个示例代码，供您参考：

<ComboBox>
    <ComboBox.Template>
        <ControlTemplate TargetType="ComboBox">
            <Grid>
                <ToggleButton x:Name="ToggleButton" 
                              Template="{StaticResource ComboBoxToggleButton}"
                              Grid.Column="2"
                              Focusable="False"
                              IsChecked="{Binding IsDropDownOpen, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}"
                              ClickMode="Press">
                </ToggleButton>
                <ContentPresenter x:Name="ContentSite"
                                  IsHitTestVisible="False"
                                  Content="{TemplateBinding SelectionBoxItem}"
                                  ContentTemplate="{TemplateBinding SelectionBoxItemTemplate}"
                                  ContentTemplateSelector="{TemplateBinding ItemTemplateSelector}"
                                  Margin="3,3,23,3"
                                  VerticalAlignment="Center"
                                  HorizontalAlignment="Left" />
                <Popup x:Name="Popup"
                       Placement="Bottom"
                       IsOpen="{TemplateBinding IsDropDownOpen}"
                       AllowsTransparency="True"
                       Focusable="False"
                       PopupAnimation="Slide">
                    <Grid x:Name="DropDown"
                          SnapsToDevicePixels="True"
                          MinWidth="{TemplateBinding ActualWidth}"
                          MaxHeight="{TemplateBinding MaxDropDownHeight}">
                        <Border x:Name="DropDownBorder"
                                Background="{StaticResource ComboBox.Background}"
                                BorderThickness="1">
                            <ScrollViewer>
                                <ItemsPresenter SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" />
                            </ScrollViewer>
                        </Border>
                    </Grid>
                </Popup>
                <Grid>
                    <Path x:Name="Arrow" 
                          Fill="Red" 
                          HorizontalAlignment="Center" 
                          VerticalAlignment="Center" 
                          Data="M 0 0 L 4 4 L 8 0 Z"/>
                </Grid>
            </Grid>
            <ControlTemplate.Triggers>
                <Trigger Property="HasItems" Value="False">
                    <Setter TargetName="DropDownBorder" Property="MinHeight" Value="95" />
                </Trigger>
                <Trigger Property="IsEnabled" Value="False">
                    <Setter Property="Foreground" Value="{StaticResource DisabledForegroundBrush}" />
                </Trigger>
                <Trigger Property="IsGrouping" Value="True">
                    <Setter Property="ScrollViewer.CanContentScroll" Value="False" />
                </Trigger>
                <Trigger SourceName="Popup" Property="AllowsTransparency" Value="True">
                    <Setter TargetName="DropDownBorder" Property="CornerRadius" Value="4" />
                    <Setter TargetName="DropDownBorder" Property="Margin" Value="0,2,0,0" />
                </Trigger>
                <Trigger Property="IsMouseOver" Value="True">
                    <Setter TargetName="Arrow" Property="Fill" Value="{StaticResource MouseOverBrush}" />
                </Trigger>
                <Trigger Property="IsDropDownOpen" Value="True">
                    <Setter TargetName="Arrow" Property="Fill" Value="{StaticResource HighlightBrush}" />
                </Trigger>
            </ControlTemplate.Triggers>
        </ControlTemplate>
    </ComboBox.Template>
    <ComboBoxItem>Item 1</ComboBoxItem>
    <ComboBoxItem>Item 2</ComboBoxItem>
    <ComboBoxItem>Item 3</ComboBoxItem>
</ComboBox>