Este códigotrabalho (quando ControlType = "dropDown", em seguida, o plano de fundoamarelo):

<Window x:Class="TestCollapsed.Views.MainView"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:c="clr-namespace:TestCollapsed.Commands"
    Title="Main Window" Height="400" Width="800">
    <Window.Resources>
        <Style x:Key="DropDownStyle" TargetType="TextBlock">
            <Style.Triggers>
                <DataTrigger Binding="{Binding ControlType}" Value="dropDown">
                    <Setter Property="Background" Value="Yellow"/>
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </Window.Resources>

    <StackPanel>
        <TextBlock Visibility="Visible" 
                   Text="This is going to be the dropdown control."
                   Style="{StaticResource DropDownStyle}"/>
    </StackPanel>
</Window>

Mas esse código nãonão trabalho (quando ControlType = "dropDown", em seguida, o TextBlock ainda éinvisível):

<Window x:Class="TestCollapsed.Views.MainView"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:c="clr-namespace:TestCollapsed.Commands"
    Title="Main Window" Height="400" Width="800">
    <Window.Resources>
        <Style x:Key="DropDownStyle" TargetType="TextBlock">
            <Style.Triggers>
                <DataTrigger Binding="{Binding ControlType}" Value="dropDown">
                    <Setter Property="Visibility" Value="Visible"/>
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </Window.Resources>

    <StackPanel>
        <TextBlock Visibility="Collapsed" 
                   Text="This is going to be the dropdown control."
                   Style="{StaticResource DropDownStyle}"/>
    </StackPanel>
</Window>

Por que não posso definir visibilidade em um estilo como posso fazer em segundo plano?